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.