Wednesday, June 8, 2011

The Science of Racing: Suspension

Yes, yes, I know this is LONG overdue. A month ago I said I would do this in a week. It's been a pretty eventful month, but now I have some downtime to get into this.

The main components of the suspension in a race car aren't all that different than the suspension on your road car. The springs and shock absorbers aren't kept near the wheel. They would generate too much drag. They are instead sheathed inside the bodywork of the car. This makes the arms of the suspension much longer. To compensate for the extra material, the linkage arms are made out carbon fiber, a lightweight high-strength material. The arms are also very streamlined to reduce drag as much as possible. (Unfortunately, in the real world, EVERYTHING generates drag. No matter how streamlined it is.)

There are a few more linkage arms than are needed to keep the car from bouncing around, however. On the photo below, which is the concept of the new oval configuration IndyCar, the pieces that are running diagonally that enter the bodywork at the top of the nose go to the spring and damper located at the top of the nose. The other linkages affect the camber of the wheel, the toe-in and out of the tires, as well as another adjustment called the weight jacker.

First, I will explain camber. As I mentioned the post about the tires, you want the entire surface of the tire to be in contact with the track. The wheels can be adjusted angularly. This would appear as the top of the tire leaning toward the car or away from the car. This adjustment is called camber. Each of the wheels can be individually adjusted so that the angle of the tire with the track ensures an even contact patch.

Another adjustment you can make, usually to the front wheels only, is known as toe, or sometimes tracking. This can be best explained by the following diagram.

Imagine you are looking down on the car from above, and that the car is travelling in the direction of the arrow. If the front of the tire is closer to the middle of the car than the back of the tire, the car is "toed-in," and vice-versa. This is essentially a change in the steering sensitivity. If the car is toed-in, it responds quicker to turning, as no matter which way you turn, one of the tires is already at least partially turned in that direction. The opposite can be said for a car that is toed-out.

As you can imagine, camber and toe affect one another quite a lot. This is one of the primary reasons there is so much practice before races is for the team to get the set up of the car down pat to maximize both speed and tire longevity.

Inside the car, the driver can change the handling of the car with a tool called the weight jacker. This is a hydraulic cylinder which affects the stiffness of the springs to change the effective weight distribution of the car. There are two weight jackers: one that controls the distribution from front to back, and one that controls the distribution from right to left. For instance, if the car is prone to oversteer (also known as "being loose" in NASCAR country), which means the rear of the car wants to snap around, you cam adjust the weight jacker toward the rear of the car, effectively putting more weight in the rear wheels. If the car is understeering (also known as "being tight" or "push" in NASCAR country), which means it isn't fully reacting to steering input as the front tires of the car have less grip than the rear, the weight jacker can be adjusted toward the front of the car to give the front of the car more grip. During qualifying especially when the car is trimmed out and is running as little downforce (and thus, less drag) as possible, you can see the driver adjusting the weight jacker before nearly every corner. If you watch the in car camera during an IndyCar race, and you see the driver put their left hand down below the steering wheel, they are adjusting the weight jacker. That was years past, however, as now, the control may have been put on the steering wheel.

So, that was suspension. I talked a little bit about carbon fiber, so I may get into that the next time I write about the Science of Racing. No promises as to when that will be. I move into my new apartment next week, and then I start my real job!

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