Selecting the Right Performance Components - Wheel Control

Part 2 Of 3
At first it seems obvious: The weight of a car keeps the tires in contact with the ground. And this is true-when the car is sitting in the parking lot. When a race car is moving, however, there are dynamic forces that change the "parking-lot attitude" of the vehicle.

When a car accelerates forward, weight can be shifted to the rear for more traction, and weight goes to the front during braking. When the car is turned, weight can shift to one side. It is the control of this weight shift that can determine traction and handling.

The timing of the weight shift is an important factor. Weight moving too soon or too late can prevent the tires from staying in contact with the track surface.

The things that have the most effect on wheel control are the springs, the shocks, and the wheels themselves.

Wheel Control With Wheels
I spoke at length with Bill Tandetsky of Diamond Racing Wheels about this. Bill's main concern is with the wheel not controlling the car. This happens when a wheel fails, at which point, car control is obviously lost. Hopefully, that is all that's lost.

"Yes, lightweight wheels will be easier for the springs and shocks to control since they have less inertia in both vertical travel and rolling inertia," says Tandetsky. "But, no, lighter wheels are for lighter cars. Most Street Stock type cars weigh 3,000-3,500 pounds.

"In my experience-and I'm not a Tony Stewart-in these cars I can't tell the difference between a 19-pound wheel and a 23-pound wheel. I can tell the difference when the lighter wheel fails. When a wheel begins to fail, it usually cracks around the bolt circle."

So, the first thing to control in our journey is the wheel. The lighter it is, the easier it is to control. However, wheel weight must be matched to the weight of the car. The heavier car needs the heavier (stronger) wheel to carry the load. Here is the way it factors on a 3200-pound Street Stock. The difference between four light (19-pound) wheels and four heavier (23-pound) wheels is 16 pounds. Sixteen pounds is 0.005 percent of the car's weight. That is five thousandths of one percent of the weight of the race car. The heavier car will better control heavier suspension parts.

Wheel Control With Springs And ShocksIn a race car the springs are not there to hold the car up off the ground; they are used to keep the wheels on the ground. If this is done properly, then the car will stand up off the ground, too.

The springs will control how much weight is shifted to a given wheel. This should be the weight needed to keep the wheel in contact with the racetrack and provide maximum traction.

When we speak of differences in springs, several things are considered. Spring diameter is usually determined by the rules or the chassis parts. Spring length or height is determined sometimes by rules, other times by the desired ride height of the chassis. The main criterion, though, is the spring rate. The rate is referred to as the amount of weight that is required to deflect the spring 1 inch.

You have probably heard the term weight shift. When a race car enters a left turn, the car rolls over to the right. The left side rises and the right side falls. Centrifugal force causes this to happen. The springs control how much shift occurs. If the right-front spring is too strong, the car will not dip enough to the right. This keeps weight from shifting to that corner. When this happens, there won't be enough weight on that corner to press the tire into the track surface for proper traction.