Maximizing Suspension Performance - CHP How It Works

Maximizing Suspension Performance Requires Scaling and Setting Crossweights. Industry Experts Tell You How

Stephen Kim Apr 22, 2011 0 Comment(s)
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Doug Norrdin: Trying to scale or set the corner weights of a car while it’s still being built often results in inaccurate data. The idea is to replicate how the vehicle will be set up in race trim. The driver must be sitting in the car, or there needs to be ballast to replicate driver weight. Make sure that all the fluids are topped off and that the gas tank is half full. Since you’re never running on empty or racing with a full tank, scale the car with a half a tank of gas. Sway bars can actually preload the suspension, so disconnect the endlinks for your baseline measurements, then hook them back up to see how much the weight readings change. To further reduce potential discrepancies, set tire pressure to where you usually run it on the street or at the track. Alignment doesn’t affect readings too much because you’re not turning the wheel when scaling a car.

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John Hotchkis: To ensure accurate readings when scaling a car, always do so with the driver in place. Next, top off all the fluids and fill the gas tank up halfway. These steps will get the car very close to its race weight. Next, even up the tire pressure at each corner since pressure variations can affect ride height. One of the most important steps is to zero out the sway bars, which requires adjustable endlinks. You can’t get true corner weight readings with the sway bars connected because they can preload the suspension from one side to the other. To zero out the sway bars, first unhook the endlinks then set the corner weights. Afterward, adjust the length of the endlinks so that the bolts slide right through with no binding or preload and then reattach them to the car. This procedure helps equalize the weight of the car from side to side, and makes track days much more fun. These are techniques that have been used for decades in road racing, but are now coming into the Pro Touring scene.

Corner Weight

Matt Jones: Corner weight, also known as crossweight, is the sum of the diagonal weights of the vehicle. To calculate percentage, add the weight of the left rear and right front corners together and divide that total by the overall vehicle weight. For instance, let’s say the left rear and right front corners on a 3,000-pound car have a crossweight of 1,650 pounds. Dividing the crossweight of 1,650 by the total weight of 3,000 yields a 55 percent crossweight percentage. Increasing the ride height at one corner will add weight on that corner and its corresponding diagonal, while the opposite corners will lose weight. To add weight to a specific corner, increase the ride height at that corner, and lower the ride height at the diagonal. If a car’s handling characteristics are unknown, always aim for a 50 percent crossweight percentage. From there, the crossweight can be adjusted to cure imbalance issues, which is particularly important for road race vehicles. Drag cars could use optimization of corner weights to equalize tire loading or to offset driveshaft torque, but I suspect the benefits would be minimal for most racers.

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Doug Norrdin: Corner weight is simply the weight each of the four car tires supports. Crossweight, on the other hand, refers to the total weight of diagonally opposite corners of a car. To help conceptualize crossweight, think of a car’s chassis as a chair. Weight moves in a vector. If you raise the left rear corner of the chair, it puts more weight on the right front leg. Likewise, this also puts more weight on the back legs, and takes weight off of the other two. Crossweight on a car works much the same way. If you have more weight on one tire than another, you’re already overloading it. The goal is trying to get the corner weights from side to side along with the crossweights as equal as possible. In the real world, a 50 percent crossweight isn’t always possible to achieve, but it’s a good target to try to reach nonetheless.

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