Weight Distribution

Weight Distribution

In this video I cover the most important topic in racing – weight distribution. Without understanding how weight is distributed on a static racecar, you may have a tough time understanding more difficult concepts – everything is based on this. Weight distribution is the foundation of racing.

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Video Transcript

Hey everyone, Matt Covert here again from howtobecomearacecardriver.com. And today I want to talk about something which is really one of the big foundations of racecar knowledge [weight distribution]. And it has a lot to do with how weight moves around a vehicle.

And I would say, I’m going to go out on a limb here and say probably weight transfer is the most fundamental thing to understand in the racecar world. But before you understand how weight moves around a vehicle in motion  you need to understand how weight is distributed amongst a static car. In other words, a car that’s not moving.

So let’s take a look at a couple different examples here. So lets start off with a theoretical racecar that weighs 2000 pounds. OK? A really lightweight racecar. And let’s just say, let’s look at the car from kind of a side view. Those are the two wheels and we’ll use that line as an approximation of the body.

OK? So obviously a 2000 pound racecar, and this is assuming that the car is perfectly balanced and we can notate that by saying that the car has a 50/50 weight distribution. OK so 50 percent of all the weight from a side view would be here which means there’s a thousand pounds over one axle and of course a thousand pounds on the other axle. Completely equal. OK?

So let’s take a look real quick, oops, going the wrong way here. Let’s take a quick look from an overhead view for a complete picture. And I know this might seem kind of basic but like I said before, this concept is one of the ones that everything else is built on. If you don’t get this than you’re going to have a pretty hard time in the future grasping other concepts and that’s just no good.

Alright so again we have a 2000 pound car. So if everything is distributed properly, and this is an overhead view, that’s a little chassis line there with four wheels, K? Let’s say that 2000 pound car has four points of contact to the road and that means each tire is supporting 500 pounds, OK? So we’ve got, let’s see if I can go back here. Yeah, so we’ve got a thousand pounds over each axle and of course that means that each wheel is holding 500 pounds.

So this is the static weight distribution of a perfectly balanced car. The problem with this is that most cars are not perfectly balanced at all. Most manufacturers that design cars don’t really care about this because a lot of cars are road going. You know the guys who are designing minivans don’t care about this but this is an excellent situation to be in in the racecar driving world.

And that’s why cars like the Mazda Miata have been so successful because they have an awesome weight distribution. The Miata is one of the them, I think most BMW 3 series are close to 50/50 if not, and I think that the, along with that, the BRZ and the F-RS, those are like 48/52 so those are all really close to being really really great cars as starting points.

OK? Now, as far as weight distribution goes, I just want to touch on the fact that having a 50/50 weight distribution doesn’t necessarily mean it’s going to be a good car. It’s a great starting point, OK? But the problem with 50/50 weight distribution is all about how the weight is not only distributed but where the weight of that car actually is.

So, and let me try to explain here, and this concept is going slightly beyond the weight distribution basic concept but I’m going to talk about it anyway. OK so let’s say, and this is the chassis, and let’s say this little square represents the entire body line of the car. A car with 50/50 weight distribution is technically perfectly balanced. But lets talk about a car that has a ton of, let’s say they have a really, a huge engine that is mounted really far forward in the car OK?

And let’s say that for some reason it also has a ton of weight way out here in the back and maybe the fuel, the huge fuel tank sits back here, something along those lines. OK, this car let’s say the motor and this other counter weight weigh the same. This car is technically 50/50 weight distribution OK? But the problem is that the weight is way out here all the way on the end. OK?

And the problem with that is that the farther away you put weight away from the center point of any object it changes the objects polar moment of inertia. And we’ll get in to that, that’s another whole video. But it has a harder time changing direction when weight is farther away from the pivot point.

So in an ideal situation, and this is why you hear about companies bragging about having motors mounted not necessarily inboard but they’re mounted farther back like this OK? And at the same time they try and keep weight out of the back so you might find like a fuel tank mounted back in here, or something to that effect.

So this keeps weight much closer to the center of the vehicle and, as such, it allows it to change directions much quicker. And you might be thinking “well how is having something on the center line, you know, weight on the center line, how does that have a hard time changing direction? Well I’ll show you just real quick.

If this is a pivot point, let’s just say you have a board here like this OK? If the weight is on the outside like this and again we’re kind of going outside the scope here but I’m going to do it anyway.

These weights, let’s say they’re each four feet away from the pivot point OK? And you’re trying to move it back and forth on the pivot point kind of like this. It’s going to take a pretty significant amount of effort to try and get the weight to change direction. OK? The way to solve this problem is to move these weights, oops, lost my fulcrum there, is to move the weights further in toward the middle.

And now it becomes really easy to change the direction of these weights as they’re pivoting back and forth on this fulcrum here. OK? This is called the polar moment of inertia. It’s the objects ability to change direction quickly.

Now, let me just explain how this applies to a vehicle. And this is really important OK? So let’s look at the side profile of a vehicle again OK? Now this translates directly to a vehicle’s ability to change direction on a pitch axis. Let me change that again OK? Vehicles change pitch all the time. Under acceleration, if a vehicle is going this way, there’s going to be more weight over this end of the vehicle because the vehicle is, or weight is being transferred to the rear. OK? The pitch is being changed.

At the same time we see the same thing under braking, you all know that experience. When the vehicle is going in this direction and the front squats down OK? Now weight transfer, this is weight transfer here, when weight is moving around a vehicle in motion, has a lot to do with how the weight is initially placed on a vehicle like you see here, in this situation.

So I know I’ve definitely gone beyond the scope of weight distribution but its all very important and everything in  racecar driving ties together so this is a really important concept to start with. I know it’s all really obvious. Oh, weight distribution, you know, those are the wheels, 50/50 all the stuff. But you have to understand it’s not how the weight, or the ratio, where the weight is mounted, but where the weight is actually on the vehicle.

I think I’m going to end there because otherwise I’m going to be going to be crossing over into other concepts.

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Take care.

 

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