Chassis Adjustments - Don't Forget!

When determining where on the race car to focus your attention for chassis adjustments, always begin by trying to fix the handling problem that occurs first. For example, if the driver says that the car is tight in the center of the turn and loose off, do not begin by trying to fix the loose condition on turn exit-even if the driver says it is the most bothersome of the two problems. This is because the handling problem that happens first often influences the handling problems that come later, even if they seem to be complete opposites at first.

Let's take a closer look at our example. Whenever a car is tight, it isn't responding to the driver's steering input. When the car is tight in the center of the turn, the driver must continue turning the wheel while slowing down until the front tires finally regain traction. Because the driver must compensate for the handling problems, he or she will almost always turn the wheel farther than you would if the front wheels were not sliding. Now when the front tires begin to regain traction, the front wheels are turned farther than necessary, and the rear end tends to break loose when the driver tries to pick up the throttle. By fixing the push in the center of the corner, the driver will have to turn the steering wheel less, reducing the tendency for the car to get loose on turn exit.

We also talked to former Winston Cup crew chief and current racing analyst Larry McReynolds. Interestingly, both McReynolds and Barham recommend swapping out the bushings in the suspension arms that connect the rear end to the chassis. In most cases, you want to use steel monoballs or Heim joints to remove any uncontrolled flex from the suspension. But this creates a rear suspension that works well when the tires move vertically but has no give to help control wheelspin. This is the case only in asphalt race cars with non-leaf-spring rear suspensions, where the rear end is locked in and not allowed to roll.

When the driver picks up the throttle on turn exit, a high-torque race motor can shock the driveline and break the rear tires loose. Typically, the driver will complain about not having enough forward bite. By switching out the steel suspension bushings and replacing them with rubber, you add a little flex to the system. Now when the driver picks up the throttle, the suspension bushings give a little bit under acceleration, which can keep the rear wheels from breaking loose as easily. Essentially, it's just a cheap form of traction control because it helps dampen that first blast of torque to the rear wheels on acceleration.

No matter how experienced you are as a racer, it's virtually impossible to remember every chassis adjustment and how it affects your race car. Even Larry McReynolds, who won 23 races as a NASCAR Winston Cup crew chief, says he depended on a list of all chassis changes available to him and how they can potentially affect the race car.

"As a crew chief, I always kept a list of everything on the car I could change in my notebook," he says. "Whenever I ran into a problem, I could look at that list and see if I was overlooking something.

"I remember that really paid off for me once when I was working with Ernie Irvan at Robert Yates Racing. It was 1993 and we were preparing for the fall race at Lowe's Motor Speedway. NASCAR had come up with the "Five and Five" rule. That means that the front valence had to be at least 5 inches off of the ground and the rear spoiler could only be 5 inches tall.

"With only 5 inches of spoiler, all the teams were having trouble getting loose in the corners. We had tried all the usual tricks but weren't having any luck. That Friday night I sat down with my list and began looking over all the setup possibilities once again. Finally, I hit on 'wheelbase.' That's when I remembered I had that car a quarter-inch longer on the left side to help it turn.

"So when the garage opened that Saturday morning, the first thing we did was shorten the wheelbase back up on the left side until it was the same or maybe even just a little bit shorter than the right-side wheelbase. That change fixed the problem of getting into the corner loose without making it push from the center of the corner on out.

"I think we must have been one of the only teams to think of changing the wheelbase for that race because Ernie led over 300 laps in that race. He really just ran away with it, which was a lot of fun to be a part of. Wheelbase isn't normally a chassis tuning change you make, but you have to be able to take advantage of every tool you have available because sometimes it can give you an advantage on the competition."