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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Few people get thinner as the years rack up, yet older folks are generally in a better financial position to build project cars in the first place than young skinny kids. That means when the resources at your disposal to build a well-balanced street machine are at an all-time high, the organic lump behind the wheel is bigger than ever, making the process of evenly distributing weight within the chassis more challenging than ever before. It’s a rather diabolical automotive truth, but fear not, it can be corrected.

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The key virtues of equally distributing the weight of a car from front to back are neutral and predictable handling. However, an often overlooked but equally important metric is how closely balanced a car’s weight is from side to side. Even a car with outstanding front/rear weight distribution can sometimes turn better in one direction than the other. Making things more complicated is that vehicle weight tends to shift diagonally, not just from front to back. To prevent this ugly scenario from playing out, you must first understand how to set the corner weights and crossweights of a car. This isn’t all that difficult, but it does require some specialized techniques, tools, and prep work for the best results. To find out how, we consulted with the most highly regarded suspension experts in the business: Matt Jones of Art Morrison Enterprises, Doug Norrdin of Global West, and John Hotchkis of Hotchkis Sport Suspension. Here’s the scoop.

Scaling

Matt Jones: Many people install aftermarket control arms, springs, shocks, and sway bars but never think twice about scaling their cars. Essentially, scaling is just another tool to assist in dialing in a chassis, and not something to set and forget. Its purpose is to optimize the weight on each tire and balance a car’s handling when turning left and right, and possibly increase traction on a specific corner when grip appears less than ideal. To get around a road course or an autocross in the quickest duration of time, you don’t want a car that understeers or oversteers more when turning in one direction compared to the other. Obviously, the impact of correctly scaling a car can be large if the car was imbalanced to start with, as it can transform a vehicle from being uncontrollable to predictable. However, if the car is fairly well balanced to start with there may not be much gain, if any.

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Doug Norrdin: Having equal weight distribution from front to rear and side to side in a chassis can make a big improvement in handling. It all depends on how serious you are and how much you’re willing to spend to get there. Although it’s often difficult to achieve, 50/50 weight distribution is always a great target to shoot for. Furthermore, concentrating the weight within the wheelbase keeps the polar moment of inertia down, which always assists in handling. The first step in scaling a car is measuring a car’s weight. A very crude way to do this is weighing your car on a truck scale one end at a time. If you weighed your car with the front tires on the scale and the rear tires on the ground, and then with the rear tires on the scale and the front tires on the ground, it would at least give you an idea of the front-to-rear weight distribution. A much more precise way of scaling a car is with a set of dedicated electronic wheel scales that measure weight at each tire. Once you have some baseline measurements, then you can start moving components like the battery and fuel cell around to balance the weight distribution. Beyond that, due to the packaging constraints of most cars, things get much more difficult. Oftentimes, things like setting the engine farther back in the chassis just isn’t practical for most enthusiasts. So while improving weight balance does make improvement at higher levels of racing, it’s probably not a major issue in a typical street car.

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