Stop and weight! A 50/50 weight distribution is not optimal

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 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 (lap times) the car is.

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) 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.

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25 Comments to "Stop and weight! A 50/50 weight distribution is not optimal"

  1. Jake's Gravatar Jake
    June 11, 2011 - 11:44 am | Permalink

    Hi

    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.

  2. Harry morten's Gravatar Harry morten
    June 7, 2012 - 2:11 am | Permalink

    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?

  3. Axel's Gravatar Axel
    December 7, 2012 - 9:38 am | Permalink

    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.

  4. NOT a 911 Fan Boy's Gravatar NOT a 911 Fan Boy
    January 25, 2013 - 3:26 pm | Permalink

    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.

  5. NOT a 911 Fan Boy's Gravatar NOT a 911 Fan Boy
    February 11, 2013 - 4:37 pm | Permalink

    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!

  6. Mike's Gravatar Mike
    July 13, 2013 - 10:05 am | Permalink

    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.

  7. Beka's Gravatar Beka
    August 18, 2013 - 3:10 pm | Permalink

    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.

  8. Beka's Gravatar Beka
    August 27, 2013 - 8:41 am | Permalink

    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.

  9. Beka's Gravatar Beka
    August 29, 2013 - 5:17 am | Permalink

    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.
    http://www.roadandtrack.com/car-reviews/road-tests/2012-porsche-911-carrera-s

    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.

  10. igor's Gravatar igor
    September 25, 2013 - 10:46 am | Permalink

    why do you think that a rear weight bias gives the tendency to oversteer? it’s the other way round…

  11. Radek Jarecki's Gravatar Radek Jarecki
    October 12, 2013 - 2:10 pm | Permalink

    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.

  12. martin's Gravatar martin
    January 16, 2014 - 9:58 pm | Permalink

    I think this will help clear up that question…..
    http://link.springer.com/article/10.1007%2Fs12239-008-0037-2#page-1

  13. Jared's Gravatar Jared
    February 17, 2014 - 7:37 am | Permalink

    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 :)

  14. March 10, 2014 - 8:36 am | Permalink

    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.

    Conclusion:

    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.

    Bye….

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