Getting the most speed out of a road race car can be tricky. A tight, sharp, right-hand corner likes the car to be set up one way; a long, sweeping, left-hander prefers the car another way. A suspension setup must favor one or the other and do it where the car can gain the most time.
Weight balance is a key component of any race setup strategy. Obviously, the number and type of left- and right-hand turns are the most important factors when looking at weight balance. Generally, equal weight distribution, a neutral setup, and suspension settings define a fast, well-balanced road course car. As usual, the recurring theme here is compromise.
Circle Track consulted Ed Ash of Ash Racing in Umpqua, Oregon, to see how he balances a road race car to win (See "Road Course Setups" in this issue for more information about Ash). The following information applies to NASCAR-style Stock Cars; it may also be useful to production-based sports car racers with the engine in the front and the drive wheels in the back.
Weight DistributionLeft-side weight distribution can often be as much as 58 percent on an oval Stock Car. A road race car's left/right weight distribution usually falls between 50 and 52 percent (either side depending if the track has more left or right turns). It's a fairly cut-and-dry issue: If the road course has more right-hand turns, then the weight is biased to the right side of the car. The same concept applies to the left side. If there's an equal number of left and right turns, then the left/right weight bias should be neutral.
Biasing the weight can be achieved through a variety of methods, but mostly by moving the weight around in the car and changing the ride height through the weight jack. Note that ride height is an important factor in weight distribution. For that reason, when scaling a car with softer springs and stiff shocks, give it a few minutes to let the shocks compress to their natural position. Some people disconnect the shocks before setting the car on a scale. A small difference can give misleading readings.
When moving objects around to change weight bias, things like the battery, dry-sump oil tank, oil cooler for the rearend, and practically anything else that has mass and doesn't require a specific location. As a general rule, never put anything unnecessary behind the rear axle because that can add to a pendulum effect when the rear end steps out of line.
Looking at the car from a front to rear perspective, road race Stock Cars generally hover in the 49 to 51 percent weight bias (either way front to rear.) For comparisons sake, many oval cars often have a front bias of around 52 percent to provide good bite on the front tires. For road courses, though, more weight over the rear wheels can transfer to the front wheels under heavy braking-and the extra weight over the rear wheels can aid traction under acceleration.
Experts disagree about front/rear weight biases. Some people want to build with the philosophy that 52 percent up front will provide good forward bite (forward bite is the key to successful turning on road courses) while others think 50/50 is the way to go. People who really get logical about it start out with 49/51 and then factor in a diminishing fuel load to balance the car to 50/50 (front/rear) by the end of the race. Ash believes a good road race car should start out close to 50/50, and then as the fuel load lightens in the rear it will move to closer to 51/49. Ultimately, everything regarding front to rear weight bias is so conditional to an individual type of car and track that no rigid set of rules apply within this narrow envelope.
Take a SCCA Trans-Am Series car, for example. These can have as much as a 38/62 (front/rear) bias because teams are allowed to move the engine back, and some clever weight placement occurs. The cars can do that because the 13-inch-wide rear tires are noticeably larger than the front tires, which in turn provide more rear traction capability for improved braking power, among other benefits. They also differ significantly from Stock Cars in terms of chassis movement, tire size, and aerodynamics, so it's not exactly safe to say that approach carries over into other types of racing.
Converting From Oval to Road CourseMaking an oval car work well on a road course is a big challenge. In fact, most people will say, "I wouldn't do that if I were you." However, it can be done, but the results probably won't be as good as a purpose-built road course car. Suspension travel is the key to making an oval Stock Car behave on a road course. For those of you attempting to do this, Ed Ash has these tips for you:
*Remove or lengthen the restraints on the rear axle, which are often used to help lift the tire off the ground during pit stops (these are chains that go from the frame to the axle). These restraints greatly limit downward travel. Now it will take longer to jack the wheels off the ground for pit stops.
*Consider using taller springs to facilitate more chassis travel.
*Check the suspension travel at all four corners. An ill-handling car may have a suspension-movement problem. Example: If you have three inches of downward travel on the right rear, then the left front would need about 211/42 inches of upward travel.
A road race-only Stock Car will have the entire body mounted symmetrically over the car, the frame would not be biased for left turn-only driving, and the A-arms will be equal length. The suspension travel package is different, so shock mounts and other suspension items connect at different spots. The entire construction is biased toward getting the car closer to a 50/50 weight distribution.
How is forward bite achieved on a road course Stock Car without having major crossweight and big antisway bars?
Comparatively, the car has less rebound resistance on the front shocks and more suspension travel (the car appears bouncy, not rigid). The goal of keeping the tires on the ground is the same, but the approach to keeping the front tires on the ground in road racing is sort of the opposite from oval racing. For example, at Atlanta Motor Speedway a Winston Cup car's left-front wheel needs to stay glued to the track. This is achieved through crossweight, antisway bars, shocks, and more; but up the road at Watkins Glen, that approach would not work, and tires would lift off the ground through the flat, sharp corners.
