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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John Hotchkis: The four patches of rubber contacting the pavement are all you have to rely on in a corner. Handling is all about taking care of those patches. If the corner weights are off and you’re driving at 10/10ths, you can get brake lockup, handling instability, and uneven tire wear and heating. The goal is to get all four tires to do the maximum amount of work you can, and the best way to do that is by getting the corner weights as equal as possible. Consequently, when building a car it’s important to put it on the scale to figure out where to put components like the battery, fuel cell, and oil tank. If you had a mid-engine Camaro, you might be able attain a 50/50 front-to-rear weight distribution, but in reality it’s difficult to achieve. Even so, many car builders are positioning engines farther back and lower in the chassis to get most of the weight behind the centerline of the front axle. Placing the weight toward the center of the car also yields a lower polar moment of inertia.

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Prep Work and Tools

Matt Jones: There are several different methods for scaling a car, but the tools typically needed are somewhat universal. They include scales, loading ramps, coilover adjustment tools, ballast, and a tire pressure gauge. Optional items include turntables, a laser leveling tool, and 1/8-inch vinyl floor tires. Before any adjustments are made, ballast equal to the driver’s weight should be in the driver seat area, and all the fluids must be topped off, with the exception of the fuel. Most people don’t race their vehicles with a full tank of fuel, so we figure that an average fuel level of half a tank should be used. Be sure to inflate each tire to the optimal pressure, which can be obtained by the manufacturer’s recommendations, or other people who run the same tire. Lastly, disconnect at least one side of both front and rear sway bars.

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The next step is to adjust the vehicle’s ride height on a level surface. If your floor isn’t level, use a self-leveling laser to find a common plane for the tires to sit on, and then use 1/8-inch-thick vinyl floor tiles as shims. Be sure to shim an area of the floor where the front lower control arm bolts will be above, as well as the rear lower control arm to frame bolts or front leaf eye bolts. These bolt heads will be used to measure the vehicle’s height. Now that the vehicle is sitting on a flat plane, the ride height can be adjusted. Start off by measuring either one of the front lower control arm bolts to the ground, and record that measurement. Repeat on the rear lower control arm or leaf eye bolts. With all the heights recorded, examine which corners need to be adjusted so that the left and right front lower control arm bolts are level, as well as the rear. If the vehicle’s front-to-rear ride height is supposed to be raked, adjust this now. Once the ride height has been finalized, double-check that the alignment is where it should be and adjust if needed. The car is now ready to have its crossweights adjusted.

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