Crew chief Randall Bradford...
Crew chief Randall Bradford helps Loomis scale the car. If you are looking for more forward bite, increasing your rear percentage can help this but it can also make you too tight on turn entry.
If your car is tight on turn entry you have several good options. First, you can raise the J-bar (essentially a Panhard bar that's curved to clear the driveshaft) at the pinion. Don't try to make a change bigger than a 1/2 inch at a time, and be aware that moving the J-bar without adjusting the length can move the rear end laterally. You can also lengthen the right-side wheelbase in increments of 1/4-inch.
Adjustments For Middle Of Turn
The middle of the turn is the area where the driver isn't hard on the throttle and is trying to get the car to rotate. These changes usually also help the entire turn.
A simple change that will affect handling in the center of the turn without compromising a lot of other setups is the height of the rear ballast. Moving the rear ballast up if the car is tight anywhere in the turn and down if it is loose. Loomis recommends avoiding the temptation to move the ballast weight back behind the rear axle as this can create an unpredictable pendulum effect. Also, even though you may have much more fuel tank capacity than you need for a heat or main event, don't add or subtract fuel as a way to adjust rear ballast. The problem with doing this is that your rear weight percentage will change as the fuel burns off. Instead, try to get a handle on how the car changes as the fuel burns off and compensate for that.
Watch out if you switch brands...
Watch out if you switch brands of tires. Although they may be marked with identical sizes, once aired up you may find that your stagger and frame heights have changed.
Another change if the car is tight all the way through the turn is to raise the right-side rear bar up one hole at the rear (next to the rearend). This, obviously, only works on four-bar rearends, but that is also currently one of the most popular rear suspensions.
Finally, the simplest-and probably most popular-adjustment when tight is simply to change the air pressure in the right-rear tire. Increasing tire pressure will help a tight condition all the way through the turn while decreasing the pressure by a half pound or so will help a loose condition.
Adjustment For Turn Exit
If you have your car working properly from turn entry through the center, you often will have few problems on turn exit that a gentle right foot can't handle. One adjustment that helps turn exit without affecting the rest of the turn too badly is the right-front spring (although it will affect turn entry some). Softening the right-front spring can help loosen up a car on turn exit, and stiffening the spring will do the opposite.
Adjustments For Forward Bite
Forward bite is the ability of your race car to accelerate without spinning the rear tires. This becomes a factor once you finally have the front wheels pointed straight ahead after you get out of the turn and you want to get down the straight.
Jack screws are an easy way...
Jack screws are an easy way to change both your frame heights and your weight percentages.
To increase forward bite you can raise the upper bars on both sides of the car next to the frame. Another option is to drop the front of the pull bar. The pull bar is what keeps the rear end from rotating counter-clockwise too much under acceleration. This works because lowering the front of the pull bar (without adjusting the length) will move the pinion angle on the front end down, which can increase traction.
Finally, you can also increase forward bite by increasing your rear weight percentage. This is simple to understand because the more weight you put on a tire the more traction you will have. But be careful with this adjustment because it can also make you too tight getting into the turn.
Don't Stack Adjustments
Finally, one last word of advice. We've just given you a lot of options when it comes to tuning your car. It can be tempting to throw a lot at your car at once. One word of caution here: Don't.
Loomis' advice is to always return to your baseline setup each week. When you get to the track and find you need to make adjustments to dial in the handling, make them one at a time and test them on the track before adding another. At the shop the next week, return your car to your baseline setup and check how much the settings have changed. If you find you are consistently making the same chassis change week after week, you can adjust your baseline to include it. Just be careful to always make one handling change at a time because as a rule, every change has secondary effects beyond the problem you are trying to address. It can be easy to make a couple of changes and have the secondary effects make the car mysteriously worse than before.