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.
Left-side weight distribution can often be as much as 58 percent on an oval Stock Car. A road race cars left/right weight distribution usually falls between 50 and 52 percent (either side depending if the track has more left or right turns). Its 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 theres 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 doesnt 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 brakingand 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 its not exactly safe to say that approach carries over into other types of racing.