There seems to be more confusion over weight distribution than any other concept of automotive performance. Much of this confusion centers around the marketing hype manufacturers use to sell their cars. For the longest time, companies like BMW advertised that they have a perfect 50/50 weight distribution. This leads a lot of people into believing that this is optimal as far as weight distribution is concerned. I guess this would raise the question: Optimal for what?
The answer to that question would be driving in perfect circles. But as we all know, we don’t drive in perfect circles. If you look at any purpose built race car from the late 1950’s onward, you will find none that have a 50/50 distribution. Virtually all modern road race cars have somewhere between 55-65 of their mass over the rear wheel. So, having a 50/50 distribution is not ideal as far as performance is concerned, but why?
It should be noted that this information applies only to rear or 4wd cars. Front drive cars do gain some advantages having a forward weight distribution, but their handling dynamics suffer…
I think the part about weight distribution that is generally not understood is how it is just one factor in a cars overall handling and performance. I have explained this in the comments to this post:
The big confusion about a 50-50 weight distribution is that it does not necessarily mean the car is going to have a well balanced feel. There are old muscle cars set up for road racing that have much more weight over the front axle, but if you drove one, you would swear that it handles better than a 50/50 Miata. The difference is, is how the suspension is tuned. Having a good weight distribution to begin with is the foundation for a fast car. But, how that car actually feels in your hands, and how it behaves around corner, is the result of tuning the suspension. With few exceptions, street cars are generally tuned to have understeer regardless of their weight distribution – they are just safer that way. When people tell you a car handles well, they may actually be referring to the tune of the suspension. It doesn’t really have that much to do with the weight distribution or how fast (lap times) the car is.
Let me stress this point again – a balanced feel to the driver doesn’t mean the car can pull high G’s. It just means that the car responds well to drive input and has good dynamic properties; all of which can achieved through suspension tuning regardless of where the weight is in the car.
Racecars actually spend a very little amount of their time in corners; in fact, most of their time is spent accelerating and braking between them. Having a greater rearward mass helps the car do those tasks better. Generally speaking, you always want to keep the weight in a car as far back and as low as possible. Here are some of the benefits of having a rear weight bias:
- Better braking.
- Better acceleration.
- Better corner entry.
- Better corner exit.
The reason for these benefits is as follows:
Better braking: The Porsche 911 (just an example, could be a GT40 or Ferrari) has always been known for its great braking ability. Many people think its because of their brake technology; but lets think about that for just a moment: Do Porsche calipers pinch Porsche rotors any differently than say Corvette rotors pinch theirs? Probably not. What Porsche does have is their massive rearward weight distribution at around 60%. Having this weight in the back naturally uses all of the tires more efficiently during braking, instead of overloading the front tires which is what tends to happen in a front biased car. Needless to say, the rear brakes do more work on a car that has a greater rear weight distribution.
Better acceleration: With more weight over the rear axle, its obvious that there is going to be more traction. Thus, the car can put down more power without spinning the tires.
Better corner entry: Cars with a rear weight bias will steer quicker and have a natural tendency to oversteer. A slight tendency to oversteer is required for proper corner execution.
Better corner exit: For the same reason given for better acceleration. A car with a rear weight bias can put the power down sooner when coming out of a corner.
Of course, it is possible to have too much rearward weight distribution which causes inefficient use of the tires and bad handling characteristics. For a long time, Porsche was criticized for having ‘bite your head off’ handling. But in those days, look at the tires and suspensions they were working with. The original 911 had skinny equal sized tires on all four corners and a suspension that wasn’t tuned as well as today’s cars. The early 911’s also lacked any type of rear wing or spoiler; the combination of of these three things – heavy rear distribution, skinny rear tires, and lift inducing rear bodywork conspired to give the car the reputation of being a handful. Surely, pushing the car through a high speed sweeper at racing speeds must have taken a substantial amount of skill and courage.
So now you might ask, “Why don’t more cars have a better weight distribution?”, well, in the real world; its hard to make an everyday car like this because it requires moving the engine very far back. This makes for very long front ends and small cockpits with cramped foot wells. This may be ok for a sports car, but is not suitable for an every day car. The other alternative is to have a mid or rear-engine. But those setups also don’t lend themselves to practicality either; and in the case of a rear-engine configuration, engine choices are generally limited to lighter weight engines. I know the readers of the blog really don’t car about practicality, but car manufactures do. Because in reality, they don’t sell many sports cars compared to their other models. They would sell even less if they were even more impractical. I mean, who would buy a car that you couldn’t even fit a golf bag into!
Food For Thought:
- Another reason why we see entry level sports cars that have poor weight distributions is because they may be built off of a shared platform. My 350z for instance is shared with Nissan’s (Infiniti) G-Series sedans; a much more practical car. This platform probably has limits on how far the engine can be set back and so on.
Note: I have found this particular post strikes a nerve in many of its readers. It’s amazing how many people have an almost religious dedication to the myth of a 50-50 weight distribution being absolutely perfect. Before you post telling me how wrong I am, please try to think how you first learned that a 50-50 distribution is ideal and if that source was creditable. Also, try to provide some proof or sources to backup your claims. Ad’s are dishonest, and magazine writers typically only have a degree in journalism and are more interested in the ‘feel’ of a car and not the ‘why’ or ‘how’. You should also know that every car that has won a grand prix or Le Mans race has had a rear weight bias since the late 50’s, and race car engineers have never looked back since.
74 Comments to "Stop and weight! A 50/50 weight distribution is not optimal"
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I’ve just bought an adjustable suspension kit for my car and was hoping to achieve a 50:50 weight distribution as I thought this was best. This article has given me quite a fresh insight and has brought to light a lot of things I didn’t realise.
My car has a rearward weight bias and is mid/rear engined. It’s a smart fortwo and I’m trying to modify it to see what I can achieve. Due to the short length of the car, it could be very hard to catch in an oversteer situation. As such, it’s set up to understeer at the limit. I’ve added massive tyres all round and this has massively affected the cornering speed amd turn in.
Although you mention a rearward weight balance has all these positive effects, it does seem to still create understeer still at the limit. Many 911’s need to use power to kill understeer on entering a bend. They also seem to be very overtyred to the point they mainly rely on grip over controlled slides due to the weight bias making them hard to catch in an oversteer situation.
I’m now not so sure as to how to set this suspension up. I don’t want to reduce braking ability or grip, but I also want to achieve a more neutral car which is what I believe a 50:50 weight distribution will give me.
Thank you for reading my blog. It seems like your a little misinformed on some of the dynamics of handling. The reason why the 911’s these days and your Fortwo push when at the limit is not because of the weight distribution, but because of how the suspensions are tuned. Because a rear weight bias has a natural tendency to cause oversteer (a trait that is deemed unsafe in street cars because it can cause a more severe crash) the geometry of the suspension and the springs rates are set up to limit traction at the front tires. For example, the first generation Audi TT’s that came out were known to be good handling cars. But after a series of accidents and litigation Audi issued a recall, which among other things, replaced the front lower control arms. These control arms took some camber out of the front wheels and tamed the ‘loose’ sporty handling of the car.
I can assure you that your rear weight bias is not the cause of the problem. Your car, like most, is not using the front tires efficiently. You say that you have an adjustable suspension kit for your car – I don’t know what this kit includes but general rules of thumb to loosen a car are to add (negative) camber in the front and to stiffen the rear springs and/or roll bars. Making the rear dampers stiffer might give you more oversteer at the entrance of a turn but will only delay the inevitable. You will also not be able to significantly affect the front to rear weight distribution with an adjustable suspension. What you can do is get your corner weights equal, but that requires special scales and is pretty labor intensive. I would also suggest reading up on suspension tuning to help you analyze the problem and to meet your goals.
I read your blog above with interest. I have a problem, which you may be able to help me with. I have a 1928 Bentley with a 200bhp engine, at the front (just behind the front axle) but the car is rather special, in that it is very light – weighing in at 850kg (under 2000 lbs). Problem is that there isn’t much at the back, other than a solid rear axle (with diff) and the fuel tank, while my leaf spring are also quite light, as they have 5 leaves not 9. The car is very skittish on corners, both entry in and exit. Having friction dampers doesn’t help (club regs preventing use of modern telescopics). Any ideas?
I have to say, I have never had the pleasure of working on a car from that vintage and have only read about them and their designs in history books.
Anyhow, its still a car with 4 wheels and tires so the laws of vehicle dynamics still apply.
From your message, I understand that the car is suffering from too much oversteer – that is, the rear of the car wants to come around.
The general rule of thumb when it comes to reducing oversteer is to soften the rear suspension or stiffen the front (which in effect makes the rear proportionally softer). But remember this is a general rule and I have seen some cars that are actually reverse of this. Its hard to explain why that is, but its most likely due to chassis flex coming into play. Here is a good guide on how to tune over and understeer: http://www.timskelton.com/lightning/race_prep/suspension/corrections.htm
My recommendation is to make a large change at one end of the car and see what happens. If you can change the roll or spring stiffness (removing a leaf or two?) at one end, do it and take a test drive. This will give you a base line on how the car reacts. On a modern car, this could be done by disconnection a roll-bar link. But be careful when making a change this big since it could make the car dangerous. Take it easy on the test drive.
I also wouldn’t be surprised if the weight distribution of your car is quite good. I don’t know your exact car, but cars from this vintage generally have the engine mounted well behind the front axle and the driver sitting close to the rear axle – generally the best layout for a front engine car.
I would also wonder about the condition of the springs on your car. Was the suspension rebuilt? Is it on original springs? Metallurgy in those days wasn’t too good and if the car is on original springs, they might have lost some of their rate over the years which is now upsetting the balance of the car.
Does your car have a recorded history? Is it known to have these handling characteristics? If not, what changed to cause this?
That’s pretty much all I can think of for now.
Once again it’s me, the motorcycle mechanic. The reason cars and bikes have bigger front brakes is that under braking, the weight transfers to the front thus giving more grip to the front tyres. A rear engined car will not have better braking because of the positioning of said engine.
I guess your right that the position of the engine has nothing to do with better braking… but usually the engine is the heaviest lump of anything in the car and does effect the cars overall weight balance. As long as the weight distribution (center of gravity) of the car favors the rear and is kept low, your car will brake better than a car with a forward bias.
Axel, please do not go calling me wrong while not providing any evidence or examples to prove your point.
But, from your logic, you would also be saying that a rear drive car with a heavy front bias shouldn’t effect the acceleration because the weight transfers to the rear…
Axel should stick to motorcycles. Optimal weight distro is 40/60 for accelerating AND braking, but I guess he knows more than multi million dollar race teams. They probably should hire him, as he will lead them to countless wins.
Even on a motorcycle, (most of which have more weight on the back wheel) under breaking there is too much weight transferred to the front wheel as is well known. The rear wheel can even lift off the ground during braking. Some of this also has to do with the force vectors wanting to pivot the vehicle over the front wheel. Having more weight at the rear of a motorcycle and also a lower C of G, would help with breaking just like cars. Sorry mechanic. As for the cornering, that’s a different story as the author has pointed out.
My main point is that in the above example you have one rubber ring that does almost all the breaking and another that does almost none. Optimal breaking would probably be somewhere closer to 50/50 weight dist. (under breaking) as well.
i dont have a motorcycle but i have a bicycle. on bicycle we have two brakes, front and back. We (us bicyclers) never use the front brake except for emergencies. This is because the front brake locks the front tire and causes the bike to try to rotate and flip over the front. It seems unsafe that motorcycles would have front brake dominance. Motorcycles are not much different from bicycles physically speaking.
Randomperson : You are simply not able to modulate your front brake , I’m a cyclist too and on road bicycle , main breaking force will be always from the front . On an Mtb it’s a different thing . Voluntarily blocking the rear wheel playing a role to give you a the trajectoire you want on loose terrain .
i dont have a motorcycle but i have a bicycle. on bicycle we have two brakes, front and back. We (us bicyclers) never use the front brake except for emergencies. This is because the front brake locks the front tire and causes the bike to try to rotate and flip over the front. The front wheels lock and you cant steer plus the bike begins to do a “stoppie” (opposite of a wheelie.) It seems unsafe that motorcycles would have front brake dominance. Motorcycles are not much different from bicycles physically speaking.
I think the reason for the more aggressive and bigger front brakes on a motorcycle is that under braking the rear wheel becomes “light”. To have better control on the rear wheel under hard braking they fit a small brake to help the rider avoid locking the rear wheel. If they would fit a brake system the same size at the back, the rider would have a really hard time not locking the rear wheel under heavy braking.
Dude, I don’t know what evidence you need and how much you have driven a 911 on a track f.e., but some of the statements you make are pretty ignorant. The 911 is a sexy beast no doubt, but the on-the-limit handling is far from perfect. You are talking about fancy suspensions and fat sticky tires and what-not, but the facts are that when you have a 50/50 weight distribution the implied balance of the chassis is perfect even with less than optimal tires and suspension. Porsche engineers are GODS and that’s the main reason the 911 is so successful, but even they are struggling to make the weight distribution of the 911 more evenly spread by moving the engine slightly forward f.e. If you were right (and you’re most definitely NOT) why haven’t other automakers developed cars with engines behind the rear axle??? “The answer to that question would be driving in perfect circles.” That is a pretty ignorant statement. The 50/50 distribution is optimal, because it makes the car’s handling neutral and that is the holy grail! If the car is RWD (with a LSD and it’s 50-50) then the oversteer is built in the chassis itself! Look at the BRZ-FRS-GT86. A car with minimal power and traction is praised all over the world, because of it’s BALANCE. I’m not even going to comment statements like: “Do Porsche calipers pinch Porsche rotors any differently than say Corvette rotors pinch theirs? Probably not.”, which makes you sound simply retarded. The mechanic guy above already told you that that’s bullshit. And don’t know of you’re 12 or something, but next time think a little before writing stupid shit, please. Cheers.
its funny that you call the author of this blog ignorant while at the same time posting misinformation as “proof” of your argument. the BRZ/FR-S/GT86 does not have a 50/50 weight distribution. it actually has a noticeable front bias. this oversteer characteristic and balance you describe is not inherent the chassis at all. it is an aspect of the suspension tuning. the American version (FR-S) has an oversteer characteristic. which is achieved through a pronounced rear spring rate bias. 137 lb.in in the front and 211 lb/in in the rear. this gives that balanced feel and ease of rotation despite the relative lack of power. it is because of this suspension tuning that allows the car to be driven in either a neutral or oversteer manner depending on how the driver manipulates weight transition through corners. without this characteristic of the suspension tuning the car actually tends to push more than remain neutral or oversteer due to the front weight bias. for proof of this look no further than its twin the BRZ which has a front bias spring rate that more closely matches natural frequencies between front and rear based on actual chassis weight distribution. this was done to make the car more stable and predictable over bumps/uneven surfaces. where as the frs has a tendency to act unpredictably over bumps due to the large disparity between front and rear natural frequency. the BRZ is less prone to do so however as it does not have a rear bias spring rate it tends more toward under steer conditions while cornering. this is all of course a perfect illustration of what the author was talking about when he said that suspension tuning can and will provide the balanced feel regardless of weight distribution. so I guess the author should thank you for proving his point with your own example. and before you question my facts/knowledge you should know I have two FR-S/GT86s both of which I race often both when they were in stock form and after I extensively modified them both and I have driven multiple BRZs both stock and modified. my knowledge of that particular platform is both intimate and extensive.
I’m sitting g in a BRZ. My not liking it is why I am looking at these things. The Porsche has weight behind the rear tires. This causes mechanical advantage in a turn, which causes oversteer issues. Although he did not say it I assume the author was not intending to imply that weight in large amounts actually behind the rear axle would help with turning. You seem to have misunderstood him. He stated that it helps in breaking and accelerating. If I am incorrect I am also sure he will correct me. My BRZ understears badly. I was one of those stupid people who bought an automatic. I am relatively sure that my suspension, and traction control systems are not set up even remotely well for the automatic. I am trying to understand why my car handles so poorly. My guess is that the added weight and maybe a change to the distribution may be responsible, but I still don’t know. I had a Miata before this. It’s body roll was extreme, but it turned and accelerated dramatically better in terms of traction (again in terms of traction) than my BRZ even with it’s upgraded tires. This car does not turn it plows.
I’m sitting g in a BRZ. My not liking it is why I am looking at these things. The Porsche has weight behind the rear tires. This causes mechanical advantage in a turn, which causes oversteer issues. Although he did not say it I assume the author was not intending to imply that weight in large amounts actually behind the rear axle would help with turning. You seem to have misunderstood him. He stated that it helps in breaking and accelerating. If I am incorrect I am also sure he will correct me. My BRZ understears badly. I was one of those stupid people who bought an automatic. I am relatively sure that my suspension, and traction control systems are not set up even remotely well for the automatic. I am trying to understand why my car handles so poorly. My guess is that the added weight and maybe a change to the distribution may be responsible, but I still don’t know. I had a Miata before this. It’s body roll was extreme, but it turned and accelerated dramatically better in terms of traction (again in terms of traction) than my BRZ even with it’s upgraded tires. This car does not turn it plows. The guy above explains this as all BRZs, but I just can not imagine they all handle this poorly… This thing should not even be called a sports car. Please don’t ask about the stupid transmission. It was a lesson in patience. This is what they had, all that they had that day, and I wanted it right then. I was stupid and impatient. I knew I would regret it, but not this much…
Inspired by the AE86, the FR-S is designed around the core goal of achieving “Pure Balance,” which begins with the strategic use of the world’s only flat boxer engine in a front-engine, rear-wheel drive configuration. The engine’s compact size and flat shape allow it to be mounted mid-ship and extremely low, giving the car a dynamically favourable front-to-rear weight ratio of 53:47 and a low centre of gravity comparable to some exotic supercars.
Thanks for posting a professional and intelligent sounding response.
Thank you for not providing any data or reasons to back up your claims, and instead call me names.
One of the reasons I started this blog was to dispel automotive myths. I have to ask you, if you try to think back to where you first learned that a 50-50 balance is optimal, where did you learn it from? Did you learn it by being an engineer on a race team? Or did you learn it from a BMW commercial? Why are you so dogmaitc about your 50-50 belief? Do you drive a BMW?
“The mechanic guy above already told you that that’s bullshit.”
I don’t know if you have noticed, but mechanics are typically not engineers or even have the slightest engineering background. The mechanic above even says he does’t even work on cars! I have personally heard the most wild stories about all kinds of things from mechanics. Good mechanics are great at fixing things, troubleshooting and even improvising. But, mechanics don’t do such a great job when I tell them to design a suspension system that keeps bumpsteer to a minimum, keeps the roll centers stable, minimizes dive, keeps the car level during cornering and still be compliant.
Here’s a good way to test a mechanics knowledge on something other than fixing things: ask one what causes your rotors to warp.
“Porsche engineers are GODS ”
No, they are not. They play by the rules of physics like anyone else. They just know the rules very well and don’t have to design cars with usable rear legroom.
My final question to you: Why does every Le-mans prototype, every F-1 car and even that crazy Delta Wing project all have more weight in the rear? All of the series those cars run in allow the manufactures to build 50-50 cars, but they don’t. They build their cars so they favor the rear more. Why?
BTW, there are rumors about the new C7 corvette favoring a rearward weight distribution….
Mate, you’re mumbling about how informal I am while adressing your raging negligence. Just chill. You demand someone to prove you wrong with examples and stats, while what you’re stating is, sorry, but a bit daft. Yes, everybody likes Porsches, because they are built like tanks, they’re fast and sexy. The problem is that, they just don’t handle very well at the limit. Yes, they naturally oversteer, but it’s snap oversteer with an anchor behind the rear wheels, that acts as a pendulum. As long as those rear wheels don’t break traction the car is tip-top. The examples that you’re trying to give with rear weight biased racing- or even supercars are reduntant, because those cars are not meant to lose traction (ever). Such cars have such high levels of grip and downforce, that when you eventually go too far, you’ll be traveling at such speeds that you have to be Ayrton Senna (or atleast a very sharp driver) to even have a chance to not crash. When the car has 50:50 W.D. it is balanced and thus handles. Handling (for me) means how the car behaves when you throw it around and make that grip disappear on purpose. Basically when you want to have fun (if you understand the concept). I will try to give you a simple enough example… The GT86 might not be the prettiest or most refined sports car, but what every petrol-head loves it for is the way it handles. That’s because of it’s balance, which in turn is simply the (read carefully) “Perfect” weight distribution. This is handling. I’m not really sure how you came up with the lame pun in the headline or why you thought you were busting automotive myths, but I hope you can accept it now. If you care about how a car feels and how fun it is, you’ll go for balance!!1 Cheers!
The Porsche has weight behind the rear tires. This causes mechanical advantage in a turn, which causes the oversteer issues you keep referencing. It’s not that the over all distubtion is poor, it’s that a large amount of weight is behind the rear axle. Although he did not say it I assume the author was not intending to imply that weight in large amounts actually behind the rear axle would help with turning. You seem to have misunderstood him. He stated that it helps in breaking and accelerating. If I am incorrect I am also sure he will correct me. My BRZ understears badly. It sucks. Maybe the GT86 is better, but neither is a 50/50 setup. The Miata is, and I wish I still had it instead of this awful thing.
Try a simple test. Remove your front sway bar. And go for a drive. You will be amazed at the turn in ability it gives you. Buy an adjustable bar and arrive at the handling balance you would like
I’m not writing about how you feel a car should handle. I’m writing about what the fastest way around a track is. Many people think that a 50-50 distribution is the end-all and most optimal setup for performance, which is simply not true. I am also not ragging on your GT86 which I’m sure is a fine handling car.
I could have used any proper race car for my example and not a Porsche 911. Would it have been better if I used a 1966 Ford GT40 which also has a 60% rear distribution and is a pre-downforce car? If all you’re saying is that a 50-50 distribution is the most fun, that is your opinion and you have missed the point of my post…
I came here because I’m considering buying a ’93 Mazda Miata. It has a 50/50 weight distribution. My question for Mr. Milmont is “Why do people swear by these cars and their handling” and many claim that they handle better than Porsches and Vettes?” I’m not trying to be a smart ass, I just want a legitimate answer because I’m also considering purchasing a first generation Toyota MR2 with mod engine, obviously more weight in the rear. Thanks.
Mike, the big confusion about a 50-50 weight distribution is that it does not necessarily mean the car is going to have a well balanced feel. There are old muscle cars set up for road racing that have much more weight over the front axle, but if you drove one, you would swear that it handles better than a 50/50 Miata. The difference is, is how the suspension is tuned. Having a good weight distribution to begin with is the foundation for a fast car. But, how that car actually feels in your hands, and how it takes a corner, is the result of tuning the suspension. With few exceptions, street cars are generally tuned to have understeer regardless of their weight distribution – they are just safer that way…
When people tell you a car handles well, they are actually referring to the tune of the suspension. It doesn’t really have that much to do with the weight distribution or how fast the car is..
50/50m weight distro makes it easier for novice drivers to NOT get into trouble. But to truly take advantage of weight shifts and higher performance, a rear distrobution bias is favorable.
I had a second generation Miata. It was awesome for me, however you should know that in stock form it leans hard to the outside of the turn. This did not bother me at all. I was able to go 83 MPH around a 35 mile an hour recommend speed turn where in the BRZ I could only go 67. The BRZ understeers the Miata really didn’t. Also I believe because of how soft the suspension was it would have noteworthy balance changes off from 50/50 when accelerating or breaking hard. I just didn’t have any complaints from these things as everything was very predictable in that car. I have ridden in an old MR2 it didn’t seem to have much lean in the turns compared to my old Miata. If that is important to you it’s something to keep in mind. My BRZ hardly rolls at all in a turn, but comparatively it also doesn’t turn at all, so there’s that as well… Both were bone stock.
The article is wrong.
First of all good weight distribution is a starting point. If it is flawed, no matter how you try, you will never be able to make the setup as perfect as with correct weight distribution.
Too much rear bias is horrible thing. It has no stability in rear under braking and has horrendous inertial and off-throttle oversteer. The original poster talks about acceleration out of the corners but does not talk about lateral G forces which the heavy rear is unable to handle and loses grip.
Porsche had to fit excessively large rear tires and introduce AWD to somehow balance the car. As a result it develops understeer in slow corners where lateral G is not high. In road cars this might be a lesser problem as manufacturers are not limited with the size of tires they can use, but racing categories are limited, therefore weight distribution is a huge factor.
Perfect distribution is somewhere around 45-55 rear, with dampers, springs, anti-rolls and camber all tuned accordingly after the distribution is correct.
Beka, Please read some of the above comments because some of the things you are talking about have been discussed. But, as stated above, I agree that a good weight distribution is the starting point.
But also understand that I’m talking in generalities. When you give an example of a race series mandating a specific tire, you are setting up a constraint that is beyond the scope of this post. But, of course you can overload the tires by having too much weight at the rear of the car. Doug Millikan of Millikan Research – a vehicle dynamics guru – says “A very simple rule of thumb for balanced handling is to ratio the tire widths to the weight distribution”, this means that the width of the tires should have the same distribution as the weight of the car. But whats wrong with ‘excessively’ large rear tires? Also, don’t forget that Porsche’s GT2 and GT3 are both fantastic handling cars and are not 4wd.
I would also like to hear your explanation of why pretty much every race car has their rear weights around 60% regardless of down force. And also how the Nissan Delta wing works at all with its rear weight distribution at 72%.
John, I again disagree, the assessment of porsche is: they are fast inspite of their weight distribution, not because of it. Porsche is constantly trying to improve its balance by moving the engine to the front slightly. You can look for that information if you dont believe me. 911s still have rear engine layout because this is a tradition and the history of the 911 brand. If porsche decided to build a competitor for 911 around a car like cayman and gave same same amount of resources, materials and time to it, it would have ended up being a significantly better performance car than 911.
When Porsche built an ultimate supercar (carrera GT) they put the engine in the middle, not behind rear axle.
All I want to say is that Porsche designer themselves know that 911 is not that perfect and they are trying to alter weight distribution themselves.
I drive a single seater with 40/60 rear weight bias which is the result of a heavy engine and it is horrible. I’m moving the battery to the front for the very same reason, this is how i found your article.
Generally I would agree that 50/50 is not a perfect distribution but I dont agree with the general pathos of the article which seems (at least to me) to claim that putting nearly the whole weight in the back is great, or that something like 30/70 rear bias is a cool thing when it is not.
When I wrote this article, I used a Porsche 911 to illustrate my point because its an identifiable car that has a greater rear weight distribution. Little did I know that I would strike a nerve with so many people. Maybe I should have used a Porsche 917, a GT-40, Maserati MC12 or even an Ferrari 458 – all of which are heavily rear biased and very fast.
One thing you said in your original post – “All I want to say is that Porsche designer themselves know that 911 is not that perfect and they are trying to alter weight distribution themselves.” – I think you are going to have to show me where they admitted to this. Please show me the original quote. I believe this to be a myth.
But tell me about your single seater. Make, model, year? What series was it designed for? You alluded that you are limited to what tires you can run, is this true? What suspension changes have you tired? Do you have experience with other open wheel (i assume open wheel) cars?
When cars (especially supercars like the ones you listed) are specifically designed with a rear-biased weight distribution, it is to improve acceleration. It is that simple. If you are talking about ideal weight distribution in regards of driving dynamics and overall ‘handling’, then a 50/50 weight distribution is ideal.
You used race cars as examples for why 50/50 weight distribution is not ideal. This logic is flawed. The engineers make these cars rear-biased so improve acceleration. Its as simple as that. Most of the time spent on a race track is not in the corners, but accelerating and decelerating between them. The race engineers know that a rear-biased distribution is not ideal when it comes to handling and driving dynamics, but they know that the highly skilled drivers that will be operating them are capable enough to handle most any oversteer or imbalance that they will face as a result, thus making the added acceleration of a rear-biased worth it.
In the case of the 911. No one with a competent understanding of basic physics can confidently say that 911’s are the way that they are because it is ideal. As someone mentioned earlier, 911’s are the way that they are as a result of tradition, and perform admirably IN SPITE of their design.
So overall it comes down to what one considers optimal. Most of the time, when people claim that 50/50 weight distribution is best, they are referring to the drivability and balance of the car. This is a CORRECT belief. However, drivability and balance are not the only factors that matter when it comes to a car. Acceleration, breaking ability, and ability to get power to the pavement, are also very important when it comes to a cars ability. Meaning that yes, a 50/50 weight distribution is optimal, but this does not mean that it is ideal for every car.
Porsche has been doing this since 60s
here is the first link, read the paragraph on B series: http://911evolution.com/911_20/911_20.htm
And a 2012 911s. Prosche designe a whole new, shorter gearbox to do that.
Porsche is moving closer and closer to 50/50 and it is not becoming slower by any means.
My single seater is Formula Alfa (not boxer) with a 2 liter TS engine. It was a mono series in Russia under the same name. you can not adjust the shocks (damping, rebound) and install different springs but tweaking camber, toe etc is obviously allowed. It is a slicks and wings formula and aero is also adjustable. I took this car to compete in local national mono series.
I had another single seater which we restored, it was a 1986 Estonia 21M, which was being built in Estonia in 80s for a USSR Formula 3 championship. That was a different car, with 80s style driver positioning (driver sitting in the front, engine closer to rear wheels). It had much better balance than my current car despite being a 20 year older design, it gave much more confidence, was more stable under braking, better over kerbs (which is not only because of balance) and you could attack harder. Unfortunately I did not drive it a lot and it was not even set up properly but despite that I felt more confident in that car.
Bika, I have already covered in the post the older Porsche models which are widely known to be a handful. Those cars did not ratio the tires to the weight distribution, nor were wide tires even available at that time.
I’m sure you are aware that everything in a car is a compromise and there is no perfect answer; but there are ‘better’ answers than others – even when it comes to weight distribution. I’m not sure why those old Porsche’s maintained such difficult handling dynamics – they obviously knew the results of what they were doing and chose to stay with it. It is in some ways amazing that any manufacturer would make a street car that is so prone to oversteer; very few street cars today have any at all (at least cars tuned for the north american market dont).
Streetcars are easier to understand these days than those 1960’s porsches, because for the most part, their dynamics are dictated by the litigious society we live in. Because of this, its hard to look at a street car, especially one as mass produced as a Carrera, and determine why they made a change. The example in this situation would be: Did Porsche move the weight distribution forward because it made a faster car? Or did they do it because it made a car that is easier to drive? Of course the 991 is faster than the outgoing model around the track, but the weight distribution is only one of the many things they changed. There is many factors outside of weight distribution that effect the overall handling balance of the car, especially if downforce is involved…
I will maintain that, in general, and if the rest of the car permits (weight distribution is just a link in the chain, and changing it alone might have a negative impact) having greater rear weight will be faster than a 50-50 car. This is not saying that this car is going to be easier to drive, nor am a specifying what that weight distribution may be. I have answered the general reasons for why it will be faster in the main post.
So that brings us to your Alfa. Someone decided the way your car handles is what they wanted or is simply good enough. The engineers that built your car most likely knew what they were doing, so why would they make a car that handles like it does? I don’t know, but maybe its because your car was built for a spec series, and because everyone has identically prepared cars, what difference would it make if the car handled one way or another? Is the race about who has the fastest car? Or is it about who the fastest driver is? It does look like your is a handful though.
You know, many formula cars that are not as heavily regulated have a ballast that can be moved to better suit the track. Goes to show that there is not one specific distribution number that’s perfect. If everything else is equal, a car should be able to accelerate and stop quicker, but overall cornering ability will be reduced as the rear weight bias increases. This is because the rear ties will be overloaded while the fronts are not being used to their potential. In this case, it should be determined by the stop watch where the best placement of the ballast is. Tracks with long carousels and high speed sweeping turns may favor a car with a distribution more toward 50-50, while a track with hairpins and quick turns will favor a more aft distribution.
But, think of the fastest car you know of. What is its weight distribution? And are the tires ratioed to its weight?
why do you think that a rear weight bias gives the tendency to oversteer? it’s the other way round…
It gives the tendency to oversteer because of Newtons first law.
Not quite. Newton laws will be responsible only for weight transfer.
If we move some mass to back of the car, rear wheels will need to work more in corner. But igor may say:, ok they need to work more but they are more vertically loaded so they have more grip. Well, that would be true for a box of bricks, not rotating tyre.
Tyre friction coefficient changes nonlinearly with vertical load. For the twice load, you don’t get twice more lateral grip.
Let’s consider a car with rolling stiffness equal on front and rear. In 50/50 weight distribution, weight transfer is equal for front and rear. So front and rear grip the same.
When we have more mass, we have more weight transfer on rear than front.
So we have bigger difference on rear tyres vertical load than on fronts. Let’s say, in the corner, FL load is 200kg, FR is 100kg, RL 500kg, RR 200kg. Front weight transfer is 50kg, rear is 150kg.
So you can see that vertical load difference between RR and RL tyres is big. Tyres always will work less efficient when loaded unevenly. So front is more efficient than rear in case of rear weight biased car. That’s why it will oversteer.
You can say that, or you can just figure that the heavy end is going to continue on its path, you know, a body in motion tends to stay in motion – ceteris paribus. 😉
The heavy rear of the car is going to have more momentum than the light front end; because of that, it takes more effort to change the heavy ends direction – why it lacks that effort is where all the tire loading stuff comes in – which you point out. Thanks for posting.
I think this will help clear up that question…..
Great discussion. I think the original post and a lot of the commenters made logical points. This the way I see it. Maybe engine layout in a racing application is also the result of practicality than simply weight distribution. No driveshaft, transaxle, less overall component weight. The resulting weight distribution, that creates larger moment forces in the rear, is both engineered out by tyres and suspension, as well as an adjusted driving style. Trail brake, mid to late turn in. Nose tucks quicker (lighter front), gets pointed faster, you get to hit the gas sooner.
I don’t think there is really such thing is an ideal weight distribution, because it depends on your (adapted) cornering technique. (Be forewarned, there is no scientific data ahead. This is purely conjecture based on reasoning).
The goal is to navigate the corner in the quickest way possible (duh). In order to do that, we should (must?) maximise lateral grip. To achieve the highest lateral G-force, we must load the outside tyres equally front-to-rear. An uneven front-to-rear weight distribution mid-corner means that we are overloading one of the outside tyres more than the other, and thus wasting grip of the less-loaded tyre. A 50/50WD MAINTAINS that 50/50WD under neutral, steady-state cornering. This is probably the best way to navigate a corner in a 50/50 car (with respect to even loading of outside tyres). In a forward-biased car (rear drive), a steady-state corner would maintain the forward bias, but putting power down correctly through the corner, would shift the weight toward the rear, bringing it closer to 50/50. This is ideal for my driving style, as I like to brake early, turn in early, and start the car rotating, and power through the corner. When done correctly, the car feels balanced.
The same can be said of rear-biased cars. To get the most out of them, it’s best to trail brake (to keep the front loaded into the corner), get the car pointed asap to the exit, and then power down when straight. If you swap driving styles, the forward-bias car will drive straight into a tree, and the rear-bias car will spin sideways into that same tree. Different WD, different driving style, different application.
The concept of an ‘ideal’ weight distribution assumes an identical approach to the corner, in this case, a steady-state corner. I suppose 50/50 is touted as ‘ideal’ in that from that neutral balance, you can access more of each style of cornering.
Rebuttals welcome. I am not a professional driver or a mechanic or a race engineer. I just like to drive 🙂
According to Porsche (we believe them) the optimum weight distribution for a sport / race car is 57% in rear axle and 43% in front axle.
All the Porsche Le Mans winners of the past (917 – 908 – 956 – 962 – 911Gt1) had this balance distribution.
911 approaching this distribution too. Year after year with new editions.
For super cars and race cars, the optimum weight distribution is 57% in rear and 43% in front axle.
Of course 50 – 50 is wrong.
I have a 400 hp Austin healey sprite E modified built for autocross. Weight dist 47/53 front/aft. 80 inch wheel base.Amazing handling but its handfull to drive!only wish that the wheel base was much longer as it switches from under-steer to over steer rather quickly ! thank god for the 6 degree + caster in the front that centers the steering when i remove my fingers from the wheel for a Milli second! and saves me every time!! Since the engine is supercharged, i also have to watch it as when to release the throttle the rear wheels engine break when i do so and the car goes to a snap over steer!My other car that i am going to use as an example today is my VW scirocco quattro. It is 530 hp space frame and uses the audi quattro drive train. weight distribution 67/33 front aft so we can see it is nose heavy! believe it or not this thing does not never ever ever understeer!! when i lock the center and rear diff it is the best handling car! i did a mistake and installed a gearbox with a torsen center diff and the car became a disgusting under steer monster! These are examples of cars from both extremes and as we can see it is the setup of the car that matters the most not the weight distribution as people think.Alignment,Diffs,for/aft height,fore/aft tire size,break distribution,power delivery and other setups are what matters the most!some examples of Cars that i have, had Porsche 914/6 GT (excellent fast corners,not so good slow corners) Renault 5 Turbo 1 ( off boost understeer,onboost oversteer) and every other car you could imagine from a prodrive prepared impreza rally car to a Mini 1275 GT! My personal favorites were my 1971 2.2 Porsche 911 E! That thing handled like a dream! once the front was lowered slightly more then the rear ( as with the r5 turbo1)!My other favorites were my Renault 5 GT turbo! This FWD monster has an amazing amazing handling! so were the fully lightened and modified evo 5 RS and impreza GC8 that i autocrossed and hill climbed them! they were both nose heavy but the center diff sorted it out and the things were glued to the ground. 50 – 50 is more of a psychological sale strategy as the average human being always feels that equal is safe and perfect while in fact it does not matter at all!
Excellent article. As to the replies above asserting that a 50-50 weight balance is optimal, I have a 1990 magazine article comparing fast cheap cars cornering speeds. All the data is properly logged, with speeds at entry, apex, exit and overall times. The cars judged to hamdle the best were the MX5 (not suprising) and Ford Laser GTX. The Laser isn’t even close to a 50:50 weight distribution, but was a close second to the perfect 50:50 MX5. The FASTEST car of the lot tested though, was the SW20 MR2. It was extremely snappy and quick to bite at the limit, but leagues faster than its nearest competitor. I’ve seen a few of these in action at trackdays, and remember watching one battling an S14 Silvia, a car much closer to 50:50 than the MR2. The Silvia was faster in a straight line and had much better brakes, but every single corner would see the MR2 pulling out a few metres lead on exit.
I’m a student in mechanical engineering and we covered pretty much what was said in this article in one of our earlier physics course. Essentially everything that was mentioned by the author is spot on. I also found it humorous that some posters are essentially yelling that “OMG GT86 HANDLES SO WELL BECAUSE IT’S SO WELL BALANCED BLAH BLAH BLAH.” First of all, you have no idea what you are talking about. They are just regurgitating what they read in the magazines. You are not an expert nor are you educated enough to comment on said topic. Second, the laws of physics do not change. The engineers are the ones that design and change certain aspects of the car (tires, suspension, aero, etc) in order to make the car more “balanced”. Third, don’t get so butthurt because your supposidely “well balance 50/50 car” isn’t actually ideal physically. If your car is so great, there is no need to defend it.
You can make a car that is FR handle as well as a MR. No where does it say that a car that is 50/50 is bad. The author is not arguing that point. But all things being equal, the MR is the ideal layout because of SCIENCE. I think it is best if some of these posters actually pick up a physics books rather than a car magazine and learn a thing or two.
Well I am a mechanical engineer and a race car driver. I drive a 996 prepared race car and the author is so correct it is not even debatable. When you are making a car go through a corner, of any radius, you are making it rotate not turn if you wish to go fast. A rear bias makes a car rotate better. Every car has a center of rotation, Can anyone guess where this is on a rear bias car? it may surprise you but on a Porsche (The rear engines are the only real P-Cars IMHO) that this point is just behind the FRONT axle. It is about where your feet are. Think of a pendulum effect. The 50/50 car rotates at the center of the car which makes for a predictable drift but a less efficient rotation and thus a slower speed in a turn,
As to the weight shift, of course it shifts differently. All cars are unique in this respect and the way you control this on any car in any turn is with trail braking and throttle over steer. There is no other way to balance a car in a turn. It is the physics of adjusting weight on the 4 springs from front to rear and side to side. These techniques make makes the back or the front heavy or light which changes tire grip. At 10/10ths of racing you are looking for balance at the limit. The better you can balance a car the faster it goes in a turn. Now a rear bias certainly gives you more grip out of a turn which is of course an advantage, Anyone who disagrees with me just lift off the gas after apex and see what happens. You will meet Mr. Wall. The only way out of a turn in any car is to lay the gas down to get traction and rear weight distribution…fast. The Porsche has an inherent advantage here as the author states.
Braking, again the author is correct, More to the art of brake set up than I care to write and most people really mess this up by adding a Big Brake kit to the front without understanding the force of their springs and the coefficient of friction of the tire they are using. They actually reduce net effective brake force by adding these kits…arghhh. The fact is that my Porsche race car chews through rear brake pads slightly faster then my fronts but I have it biased to use maximum net brake force. Why do you think race cars add a brake bias? To add braking to the front? Almost never. The pros adjust bias to the back as tire pressures come up. Again an entire white paper here. The bottom line is that a 50/50 car is easy to drive for a novice an feel “lighter” but it will never beat an equal rear bias car around a road course. Cheers, Scott
I think there is a point of this that everybody seems to be overlooking. The majority of cars have the engine in the front, and of course the drivetrain too. Sports cars tend to have the diff in the back of course, which shifts some of the weight back, but in essence most real world cars are naturally weight-biased in the front. Where BMW and Nissan have an advantage is their engines are located behind the front axle so the near 50/50 distribution is of course much better than a 60/40 front bias. It may be more advantageous to have 55% rear but in reality this is not achievable for a practical 5 passenger vehicle so 50/50 is the closest we can get to perfection without sacrificing practicality
Very good discussion!
I enjoyed all the posts. Just thinking a bit more after RACER LUKE’s note: Yes probably when we hear “ideal” 50/50 WD in articles and ads that is usually a BMW-Nissan GTR-Aston Martin or Mercedes C coupe when they try to sell a nice sporty executive car. And some AWD Audis and Subarus. They try to spread the drivetrain between the front and the rear of the car using rear diff or transaxle and we are happy because it’s not a cheap and slow 1970’s Fiat with more weight on the front.
But when Luigi, Sofia and 3 bambini is travelling together it might be a rear biased weight distribution. If Sofia is fat you might want to put the battery on the drive side.
So how about a 4 seater “sports car” which is marketed for the public having a “perfect” weight distribution? Automakers, engineers have to consider the 30 year old male single manager as the potential buyer for the car but also take into account the family guy who wants to be the 9 year old when having fun in the snow with the kids on the backseat.
Then we could start calculate the % difference between the permissible gross weight and when a skinny jeans boy racer with half a tank petrol taking it for a spin.
Just sticking with those lovely Porsches everybody loves the 911’s are 2+2 seaters with very small front luggage compartment. Probably it’s easier to alter the Cayman’s weight bias with two slightly larger boots on either end of the car.
It’s slightly off topic but having any given weight distribution and wheelbase combination with more weight centralised near the centre of gravity is always better for faster cornering versus having the same WD and more mass built far away from the middle of the car. (Basically putting the driver and the engine in the middle gives smaller moment of inertia than having a transaxle layout and a comfortable legroom. In theory. That is making the car easier to turn.)
The first time I learned about the 50/50 ideal was an article on BMW Films, the ones with Clive Owen and various other celebrities. It was quite convincing, and I believed it for a good 10 years. In the past year, when I finally started going to the track, I began to have my doubts. A little googling led me to your article, and you couldn’t have put it more clearly. 50/50 is predictable and balanced, but by no means the ideal.
This post is old and I’m late to the party here but would appreciate a response…
What about center of gravity? So lateral load in corning would be disproportionately put on the rear. The Physics 101 version would say that the extra weight back there cancels this out but in reality it’s not so linear. Hence the extra tire width out back, I’m guessing. Additional, a stiffer roll bar would be required out back, no? Not sure what this does to some of the turn-in dynamics.
Admittedly, I drive both an E85 Z4 and a Spec Miata on the track so I’m apparently biased. 🙂
But speaking anecdotally, the 50/50 weight and the slight steady state (aka skippad) minor understeer seem to translate well on the track. On entry, mild trail braking turns the car into a mild oversteerer and helps turn in. Once I’m back on the throttle, the power to the rear again turns the car into a mild oversteerer as I throttle steer to track out.
I’m not totally sure what you mean. Yes, steady stat turning performance like on a skid pad does suffer with greater rear weight. But like I said in the article , thats a moot point since most tracks do not have this kind of driving. The benefits gained by having shorter braking distances and the ability to put the power down sooner usually outweigh the negatives of having more rear weight.
The discussion of roll bars is beyond the scope of this article and is more about suspension tuning. But just because one end of a car carries more weight does not at all mean that end needs a stiffer sway bar.
50/50 means little. It’s not hard to weight a car 50/50 and have a large mass extending out behind, or in front of their relative axes. It is this mass that causes the problems with the 911. Keeping the vast majority of the vehicle mass within the front/rear axes and equal front to rear is the most important thing one can do to achieve great handling, followed by weight distribution. Bear in mind that a static weight distribution of 50/50 will change dramatically from power on/off, braking. As for having extra weight over the drive end (front or rear) to aid traction during acceleration, remember that a lighter car will always out accelerate a heavier car, all else being equal. Don’t discard the notion of control via the throttle pedal either, It’s the single most important part when cornering/accelerating on the limit
Having the great majority of the vehicle mass in between the front and rear axes would have to be the most important thing to achieve if you want great handling, followed by weight distribution – 50/50 is good. As for having more mass at one end to assist acceleration/braking, that defeats the above. Remember also that static weight distribution changes dramatically under acceleration/braking. Eliminating weight overhanging the front and rear axes, and using throttle and brake pedal properly will solve many issues.
Those touting ’50-50 is always better’ are so silly. Suppose you have a variety of RWD vehicles and to simplify (and to better understand what issues you’re actually dealing with) you are doing separate testing of acceleration-traction, braking-traction,and cornering-traction. I guarantee you’ll find that in hard-acceleration traction testing, extreme rear weight bias is best. In fact if you’re not cornering you want 99.9% of the weight on the rear wheels AT the time of acceleration. (This does not at all mean 99.9% rear weight bias because acceleration un-loads front wheels). Now let’s test braking traction. On a vehicle (I’ve tested it on my bicycle but this would apply the exact same way on a four wheel vehicle if it had such a high center of gravity) IF you pitch 99% of the weigh forward to front wheel, you need to stay off the rear brake. Likewise, if you could get the bike to have 50% of the weight on the front wheel 50% on the rear DURING extreme braking that would be ideal for braking traction using front-rear brakes (assuming identical tires front/rear). Now let’s talk cornering at steady speed: of course 50-50 is best for a bike or car assuming tires are identical.
Every car is making compromises to try to get pretty close to these ideals but may prioritize one (say, acceleration) or another (steady speed cornering) and also might prioritize stuff like seating space
You are totally on the money. I regularly race FWD DC2 Integras (62:38) and also a 911 Turbo (38:62, 996 gen). The Turbo is AWD but with a viscous coupling that only shifts more than 5% of the torque forwards after the rears spin up, so effectively has RWD handling unless spinning up the rears. I have also had several BMWs (e34 540i and e38 750iL) with near 50:50.
All these cars have exceptional handling for their types (even the 750) but need to be driven differently to get the most out of them. The beemers you drive hard in almost the same manner as you would while commuting, and they’ll drive like they are on rails without you thinking about it, but they are a bit cumbersome when swift direction changes are asked of them. The Integra is spectacularly forgiving and easy to drive, but understeers easily under power so in tighter corners it benefits from some footbrake or handbrake while giving it gas on the way out to keep the nose turning in. The Turbo also understeers on the way out as the front lifts and some torque is thrown forwards, but to a much lesser degree – so I just initially aim inside the track out point then carry her out there on the gas. The Turbo would understeer terribly on the way in to the apex though if not trailbraked quite deeply, so it is almost always trailbraked. As you say above, rear weight bias helps get you around a course faster but does demand considerably more skill and attention from the driver to keep it on track and pointed forwards.
I’ve been reading car mags for quite a few decades now, and have watched more Top Gear episodes than I’d care to admit to so I understand that 50:50 is ‘received wisdom’ and the most comfortable for commuting. But with similarly well sorted suspensions I’d be reaching for the rear-weighted option if trying to set the fast qualifying times or win races. And if say, I had to drive an 8 hour enduro single handed, then a FWD option would start to look pretty attractive as it is hard to sustain the level of concentration needed to keep a car like a 911 Turbo or a mid-engined car on the limit and out of trouble for that sort of duration. But that same challenge is makes them so rewarding to drive for shorter stints.
Hi guys a bit of help would be appreciated we race a grass roots local league called dirt circuit . You can youtube footage easy dirtcircuitsa. Any way i havd just built a vz monaro with ls1 1200kg 270rwk we are limited to 225 tyre size its our only restriction . We race on multiple surfaces usually wet clay limestone with warer we get plenty of slip and ruts but after a few laps rubber lays down and advans 048s grip well ! The fastest cars i race are a vw with a ls3 a bmw 1hzj i think ?? Wrx ls2 my problem is take off and out of corners !!! Only thing i can think of is adding weight to rear but where and how much ? Or can i adjust my front coilovers to compensate ?
Just to clarify a few misunderstandings on the part of many posters here…
All the points raised by the author about the benefits of a rear-biased weight distribution on a RWD car are CORRECT. To summarise:
– Better acceleration as weight is over the driving wheels (rear). This can also help earlier corner exit. However, this is purely from the consideration of traction and doesn’t take into account centrifugal forces acting on the car through the turn.
– Better braking because brake force is distributed better between front AND rear, instead of being more front-biased.
Now there’s a whole lot more involved in engineering a car’s handling attributes than simply looking at linear traction (frictional forces acting in the longitudinal axis of the car). This is one reason why even mid/rear engine sportscars don’t have their engines positioned all the way back.
There IS a context in which 50:50 weight distribution is IDEAL. If we are to consider ONLY the lateral (centrifugal) forces on a car during cornering, the ideal weight distribution would be 50:50. This is the weight distribution which would provide neutral stability in a car going through a constant radius turn, at a constant speed. As you increase the lateral forces (increase cornering speed), a front-heavy car would lose traction at the front, causing understeer. A rear-heavy car would oversteer. a balanced weight distribution would do neither as it would lose traction at the front and rear equally. These 3 characteristics translate into the steering stability of a car when it loses traction mid-corner.
see this picture: http://image.slidesharecdn.com/basicaerodynamics-110324082120-phpapp02/95/basic-aerodynamics-35-728.jpg?cb=1300955896
– understeer = positive stability. when you reduce speed, the car will return to the original turning radius
– oversteer = negative stability. once you start to oversteer you continue to oversteer. This is neglecting the dynamics of counter-steering.
F1 cars are en excellent case study of how engineers try to find the best weight distribution taking into account ALL the variables. The loss of traction at the rear during cornering, is what will allow the centrifugal forces to rotate the car and destabilise it mid-corner. But the acceleration and braking benefits of a rear-heavy car ARE desirable. Amongst MANY design features that they encorporate to achieve the best possible lap times, a few basic principles applied are:
1. rear-biased weight distribution to improve braking + cornering.
2. aerodynamics to put more downforce on the rear driving wheels, and hence improve linear traction.
3. long wheelbase so that the lifting effect of the rear end during braking is minimised. A longer moment arm creates a larger counter-moment against this lifting effect to keep traction on the rear wheels.
4. the longer wheelbase also reduces the angular velocity of the oversteering car about its normal axis by increasing the radius of the rear end from the normal axis. This means that that recovery of control by counter-steering or regaining rear traction is easier.
So in otherwords, although rear-bias weight distribution is not ideal for steering stability, they use other design features to remedy this problem such as suspension tuning (compression, rebound, etc), and steering geometry (wheelbase, track width, toe, camber, etc.).
– Currently 2nd Year Bachelor of Mechanical Engineering
– Graduate with Bachelor of Aviation Degree
– Always been good at mechanics (physics)
– Car lover
I’m so glad somebody chimed in about the actual handling characteristics of a 911. Every statement made in favor of more weight over the rear cited the 911 as evidence in favor when in fact the 911 is the PERFECT example of more weight over the rear being a problem. 911’s brake well because all that weight over the back allows them to have a larger deceleration force in the rear than typical cars have which keeps them from rotating while braking. And of course, as the 911 illustrates perfectly, the larger rearward mass has a tendency to cause the car to rotate while acceleration out of a turn.
In closing don’t setup your car based on advice from people who may not know anything about physics at all. A perfect example is the post directly above mine from professor Jay and his bicycle. He suggests we want ALL the weight on the back while accelerating which is the definition of a drag car doing a wheelie. The front tires can’t steer the car if there’s no weight over them for crying out loud!!!
Only those not clever enough to do the math for themselves will argue that 50/50 is always the ideal and that this is why the mazda miata is such a nice car. Meanwhile they are unable to explain why 50/50 was not done for most Ferraris, Lamborghinis, Lotus’…
Porsche aren’t moving the engine to change the weight bias. They’re working to reduce inertia which is the big drawback to having the engine stick out beyond the wheel axis.
In kart racing, 48/52 or 47/53 is the preferred bias.
To everyone who wants to argue the whole weight distribution, Per summed it up pretty well in that its in the math (the math and the actual physics compliment each other perfectly).
More rear weight bias in a race car will typically give a faster car (assuming that the suspension is tuned properly as the write of the blog has pointed out multiple time).
This however is different then a street car due primarily to the way that we drive on public roads vs. how we drive on a track. As it was said, most track cars spend most of their time accelerating and braking and the rear weight bias (as it was pointed out) gives advantage in both cases as it makes more efficient use of the tires during the events. Example, look at any pick-up truck. With no weight in the bed of the truck, its very easy to spin the tires but add weight and its not so easy any more.
The same thing applies during braking. Yes weight dynamically transfers forward during braking but more static rear weight means more dynamic rear weight during a braking event and thus the rear tires can do more braking work of the total required to slow the car.
Since the motorcycle mech. guy brought it up, yes most cars have larger front brakes then rears cause they do more work and thus generate more heat BUT this is not always the case. Many modern mid/rear engine cars have nearly identical disc’s front and rear because during heavy braking events the brakes are more evenly loaded.
In case that guy is still reading this, you have to understand that there are some KEY differences between a motorcycle and a car. For one, a Motorcycle has a MUCH SHORTER wheelbase and two, it has a much higher center of gravity when the rider is on the bike. Between the high center of gravity and the short wheel base, MUCH more weight is dynamically transferred during braking events. Same thing applies during acceleration which is the reason why its so easy to do stoppie’s and wheelie’s.
All in all, the lower the center of gravity and longer the wheelbase (and track width), the less weight that is transferred during a dynamic force (g-force applied laterally or longitudinally). The less weight that is transferred, the more evenly loaded the tires are and the more traction the car can get from the tires.
For example, lets say that you have a mid engine car that weighs 2800lbs and has a weight bias of 42/58 (front / rear). This would mean that the front end weight is 1176lbs and a rear weight of 1624lbs and lets say that this hypothetical car has a center of gravity height of 15″ above ground and we will say that this car has a Wheelbase of 100″. During a 1g braking even (all in all, a typical professional well designed track car), there is only 420lbs of dynamic weight transfer (1596lbs front and 1204lbs rear). Tire traction is directly proportional to the vertical load on the tire (i.e., a tires traction is directly proportional to the weight that is on it). This however is a case of diminishing return too. This however still means that in this dynamic situation the weight bias is 57% front now and 43% rear (i.e., the car still relatively balanced in weight over the two axles and the rear tires can do more braking work and the fronts are not over worked).
Now lets look at the same car but reverse the weight to be 58% front and 42% rear (say a front engine / rear drive car) and we’ll even keep the same low center of gravity and 100″ wheelbase. In the same 1g dynamic situation, the dynamic weights are now 2044lbs on the front axle and 756lbs (i.e., 73% front and 27% rear). Now the front tires are being heavily worked during this breaking even and the rear are doing very little work. So YES, the engines position (really static weight distribution has a MASSIVE effect on braking ability.
As for the handling. for a street car, the closer to 50/50, the better and is really why Porsche is trying to push the engine forward (Per is right here too though in that its also to lower the Inertia) . For a race car though this is not true. This comes down to the driving style differences between the two types of cars and their intended uses.
Here is why, in a racing type situation, we typically use a style called trail braking (in a car its similar but still slightly different then trail braking on a motorcycle). By having a slightly heavy rear end, the trail braking allows for the weight to be roughly 50/50 as we pass through the apex of the corner which is what we want. It ALSO allows us to brake later at the end of a straight before corner entry which again is something that we want so to run faster lap times..
Since in normal street driving we are taught to brake well before the turn and release the brakes before we start to turn, we doing get that more balanced distribution during the turn which is why automotive manufactures try to get very close to 50/50.
In conclusion, due to driving style, this article is both right and wrong. Its right in the sense of a track car and driving style associated with it, but its partly incorrect as it pertains to a street car and the typical driving style of said street cars.
Oh and to Marc Lewis, those weight distributions for karts is heavily influenced by the fact that they have very low center of gravity’s. This very low center of gravity (as explained above) cause much less dynamic weight transfer so the resulting case is not going much past 50/50 during braking.
I read your great article with much interest and i truly understand all the information given in it.
question ( how i got to this article in the first place): i am researching to find ‘the perfect foundation’ car. There are a number of constraints that i would like to state here.
1: the above mentioned slightly aft biased weight distribution
2: rear wheel drive
3: four(ish) seater, preferrably smaller to medium sized hatchback so i can bring a mountainbike in the boot.
4: well below the 10k $ mark (I have other passions besides owning a fast streetcar ;-).
5: not a gas guzzler during normal rides.
It can be old(ish) but preferrably something that isnt too exotic in my part of the world (continental europe). In case parts and upgrades are needed.
My plan is to slowly upgrade this ‘foundation’ into a solid fast street and maybe trackday machine.
Hopefully i will harvest some interesting feedback here.
Thanks in advance.
I feel the correct information on this topic is long overdue. You have to be living under a rock to miss the traction advantage the 04 Ford GT had over contemporary Vipers. And adding more horsepower to either car made it more obvious. If 345 tires aren’t enough, perhaps the engine needs to sit closer to them. On a similarly rebellious note, the universally taught apex technique is wrong. Consider straightening the record on that too if you enjoyed writing this article.
Praise to you John for trying to explain why 50/50 is not optimum.
Unfortunately, alot of rev/gear heads are simple, stupid people.
They have no idea what they are talking about, but want to sound cool.
People if you think 50/50 is optimum, do us all a favour and end…
I hope you still monitor this blog. I have a 2008 Audi TT MK2 with the 2.0 motor and FWD. I did some moda this summer that reduced the weight about 200# maybe from the mid section to front. I did KWs coilivers and have the drop about level on all four corners. I have not had all corners weighed but now since I’ve placed my factory wheels back on for winter it feels as I’m driving on a layer of air. Could this be that I need to raise the rear a bit to get some more weight to the front?
I disagree somewhat but it’s a matter of taste. 50/50 is a very neutral car and very predictable. Thing about the Porsche’s is they demand a different driving style. Hard braking down hill in a Porsche can be sketchy and generally trail braking in general. The heavier rear wants to comes around. It does have alot of traction out of corners and the turn in is amazing as well as brakes. A lot of mid engine car’s are picky about turn in speed or you will get understeer. The corvette c7r ( racing version) I believe is a 50/50 distribution car and is a very successful winning le mans multiple times and 2016 weathertech sports car series, 12 hours sebring, Daytona etc. 50/50 makes a very predictable neutral car which is very important in racing as well.
The original article is shockingly accurate from a physics and engineering perspective. I don’t think I’ve ever read something on cars that Isaac Newton himself would understand and approve of, until this. A few notes, comments:
Porsche knows how to make cars. The weight distribution of their race-winning cars (cited above) should be more convincing than that of the 911. The 911 (I’ve driven one for 20+ years) was initially designed as a compromise. They knew that a mid-engine (engine in front of the transaxle, rather than behind it as they did on the 911) layout would perform “better.” And as the author clearly pointed out, “better” involves many things, including accelerating, braking, handling feel, and actual handling performance.
But Porsche wanted the two small rear seats in the 911. That’s why it’s rear-engined. Battery in the front trunk, suspension tuning, wider rear tires, etc. all are making up for this excessive rear bias. And now it is an iconic design/brand, so they’re sticking with it as their flagship (after trying to phase it out and replace it with the front-engined, water-cooled, V8-powered 928 in the 80’s-90’s).
Porsche can make things work. So that’s why they invented the rear transaxle on their front engine cars, to keep weight balanced, ending up with close to 50/50 in those compromises.
For those interested in understanding the physics, a perhaps useful concept is that if the chassis can be assumed to be rigid, all the mass properties boil down to the mass, center of mass location, and moment of inertia (matrix). So there is nothing special about where exactly the mass is distributed; it only matters how these basic properties are affected.
And to go along with that, a suspension tuning kit might change the handling, but it won’t significantly change the weight distribution unless you put it in the trunk and leave it there. Corner balancing may change the weight on each wheel, but does not change the overall front-rear or left-right mass distribution.
i dont have a motorcycle but i have a bicycle. on bicycle we have two brakes, front and back. We (us bicyclers) never use the front brake except for emergencies. This is because the front brake locks the front tire and causes the bike to try to rotate and flip over the front. Especially when the brakes are slammed hard. It seems unsafe that motorcycles would have front brake dominance. Motorcycles are not much different from bicycles physically speaking.
The Tucker 48 is a good example since it had a rear engine and 40% weight distribution of front wheels. Many of these cars handled very badly. But after front and rear anti-sway bars were added those cars handled very well. Beverly Ferrara said that his Tucker handled almost as well as his Corvette.
Good info. The perfect 50:50 doesn’t mean it’s ideal to have that but it just says it’s perfect equilibrium between the axles. It doesn’t mean it’s ideal to have a perfect equilibrium. But they may want you to believe that anyway. This is good for off road in case of suv’s, and also the car will want to rotate around the CG but yes, a bit more to the rear is a better start for a fast RWD car. This is of course one of the ingredients which if it’s there it’s better. For a frontally mounted engine. A 50:50 is very good. There are very few cars with more weight to the back ( ex Mercedes gt r) but still around 50:50. So this is roughly the best you can get in terms of balance. For a rwd car more than ~52% on the front is not that great. The suspension is also important. Basically you want a double-wishbone or 5link for the best grip. For example Audi A4/5 has a poor balance but good suspension while bmw 3 series has a good balance but a cheaper suspension (the front grip is still good).
Of course a well tuned car with more front weight can have better grip than the miata but it probably won’t be better than a cup car miata unless it uses an effective aerodynamic body kit (like i.e. a hillclimb car)
Increased weight never helps anything. While grip goes up with wight, it does not proportionally.
I understand that more weight at the rear makes the car oversteer because it works like a pendulum, but I always thought that lighter rear were more propensity to oversteer because it has less grip on the tires. It was also the same logic I was using when trying to understand why a car tends to oversteer when braking.
Could you explain to me if that makes any sense?
There is different kinds of oversteer. There is the kind that happens while cornering and the kind that happens under power. a light rear has a propensity to oversteer on the throttle. This is because the car cannot put the power down. This is the case with pretty much all muscle cars. But in a steady state corner, a car with a light rear will tend to understeer.
Under braking, i think what happens is the cars tend to oversteer because the load on the rear axle tends to reduce to almost zero. At that point, its easy for it to break traction.
Static weight distribution doesn’t mean much because on track the car is either braking or coasting (very little) or accelerating.
Rear bias weight distribution is better for number of reasons BUT having too much rear weight means in mid turns the car will understeer on power, this is exactly the tendency of rear weight bias car.
Also not every corner is short many of them are slightly longer i.e the mid turn is big takes time to get wheel straight AND tbis is where rear weigh bias will induce power on understeer. on corner like this having slightly more load on front like 45-55 is much better than 40-60.
Not to mention how the rear weight car actually makes their life harder just because of their weight
To make cars predictable in turn-in you need aggressive rear wing BUT that same rear wing gets in way while putting power (remember to get maximum output drivers get on power even before steering wheel is straight) And this problem is even more apparent in long turns where drivers needs to stay on power to maintain max cornering speeds (Gs)
The setup window becomes much smaller with such disproportionate weight balance.Porsche uses good amount of rake to keep the front slightly lower
So overall to get maximum cornering speed closer to 50-50 is ideal so that all tyres are at their max grip.
BUT IRL having some power on understeer isn’t bad so IRL i would definitely have a 911.
Also there is a difference in rear engine rotation and mid engine rotation even if they have SIMILAR weight bias.
To put it simply a 911 is easier to get oversteer with.especially on braking but it is slightly more slower oversteer than mid engine oversteer because mid engine oversteer is like a spin rather than pendulum effect. so Mid engine might lose traction later BUT when it does it will spin faster AND more 360s than rear engine one.
Maybe I missed it, but I haven’t seen any discussion of driver weight/position. Or how the weight is distributed in general. Both affect driving characteristics. Is most of the weight near the CG (center of gravity) or not? I believe I read that the ideal for cornering would be for the weight to be very near the CG, as this minimizes the moment of inertia and thus torque required to turn. I’d really like to hear more on this topic. Do I really need to loose 10 lbs and scoot my seat up to achieve cornering nirvana?