Cotton Spry weighs nearly 200 pounds once he's put on his driving shoes, protective suit, gloves, and helmet. The Legends Car he races weighs just under 1,100 pounds without any lead. When you add in his weight, including his personal safety gear, he's already close to the 1,300-pound weight minimum INEX mandates for the cars. So, since Spry has less than 50 pounds of lead ballast to move around and work with, he cannot be doing much more than making laps while others race, right?
Actually, that statement couldn't be more wrong. Spry is the owner of four national championships racing Legends Cars in INEX's Masters Division. Surprisingly, he's no specialist either: Three of those wins came on asphalt, while the fourth was on dirt. Much of his success comes because he is great behind the wheel, but the veteran driver is also very adept at making the adjustments to maximize the performance of his car.
"You can really do a lot with a little when it comes to a Legends Car," Spry explains. "These cars are so light that a small change can make a big difference in the way the car handles."
Three Categories Of Weight DistributionIn almost all types of oval-track racing, rules mandate a minimum weight. So when discussing weight distribution, racers generally talk in terms of percentages. The best way to measure this is with a set of dedicated racing scales. They are precise, dependable, easy to use, and do many calculations for you. Yes, a set of digital racing scales can be an investment, but it is a valuable chassis-tuning tool.
When it comes to weight placement, there are three general measurements that are discussed in terms of percentage of total weight: left-side percentage, rear percentage, and crossweight (also known as wedge). Left-side weight is the total weight on the left-front and left-rear wheels divided by the total weight of the car. Obviously, since you are always turning left in an oval-track race, centrifugal forces are always trying to roll the car over on its right side. Concentrating more weight on the left side of the car helps the dynamic loading to be more balanced on all four tires as the car rolls through the turn and increases total grip.
Rear percentage works in much the same way. When a racer applies the brakes before entering a turn, inertia places extra loading on the front tires. Moving more weight to the rear of the car helps even the loading while the car is braking and keeps it more stable on turn entry. INEX wants to keep racers from spending too much money looking for ways to shift weight around in their cars as they try to find an advantage, so the sanctioning body limits both left-side percentage and rear percentage in Legends Cars to 52 percent or less.
Crossweight is the third category. It is calculated much like left-side and rear percentage but also has a few important differences. To calculate crossweight, simply add the weight on the right-front and left rear tires and divide that by the total weight of the car. Don't forget to include the driver's weight. Unlike left-side percentage, it isn't immediately obvious how much crossweight you need. Many racers struggle week after week trying to find the right amount of crossweight for their car and driving style. As a general rule, adding crossweight-or increasing the percentage of total weight over the right-front and left-rear tires-will tighten up a car. Decreasing the crossweight causes it to be more loose (the rear tires will break traction before the front tires).
Making AdjustmentsIt can get quite frustrating if you try to limit yourself to moving lead ballast around in order to tune all three percentages. Every time you move, add or remove weight to get one percentage closer to where you want it; that change also affects the other two percentages. Thankfully, there is an easier way.
When it comes to left-side percentage and rear percentage, the only way to make adjustments is to move weight around in the car. Sometimes there is only so much you can do. Spry, for example, races with his rear percentage at 49.5 percent. He'd like to get more weight in the rear of the car, but all of his lead ballast is back there already. Crossweight, however, can be affected by changing a car's ride height at specific corners.
The easiest and best way to do this is to adjust the spring collar on the vehicle's coil-over shocks. The shocks feature either a threaded body or a threaded tube that fits over the shock body, and the spring collar (the upper mounting location for the spring) is threaded onto that. By spinning the collar, you can raise or lower the top of the spring. Threading the collar down the shock pushes the spring down and raises the car's ride height for that corner. Threading the collar up has the opposite effect.
When you push the spring down to raise the ride height at that corner, you also increase the amount of weight on that wheel and the wheel to its diagonal. This means if you raise the ride height of the right-rear corner of the car, you are increasing the weight on the right-rear and left-front tires. You are also decreasing the loading on the left-rear and right-front. This has the effect of decreasing the crossweight percentage but does not change either the left-side or rear weight percentages.
Changing just one corner of the car in order to tune the crossweight also changes the ride height at that corner, but there are ways to change the crossweight without affecting ride height. This is especially useful if you are already at the minimum ride height according to the rules and wish to make a chassis adjustment. Instead of making one change at one corner of the car, you can instead make small changes at all four corners. For an example, let's pretend you wish to decrease the crossweight and plan to lower the left-rear corner of the car by one turn on the shock collar (rotating it counter-clockwise 360 degrees), but the car is already at its minimum ride height. You can affect the same crossweight change by dialing down the shock collars on the left-rear and right-front corners of the car one quarter of a turn and up on the shock collars on the right-rear and left-front corners of the car one quarter of a turn each.
How It WorksUnderstanding how crossweight changes affect a car can be a bit confusing at first, but it is fairly straightforward. Increasing crossweight not only tightens a car up, but it also increases forward bite when accelerating out of a turn. That is because it provides additional loading to the left-rear tire. Now, instead of the right-rear tire doing all of the work as the car accelerates out of the turn (which makes it easy to overpower and cause a loose condition), the left-rear shares more of the load and pushes the car forward more evenly.
Adding crossweight tightens a car on turn entry for the opposite reason. The right-front tire is already bearing most of the load as the car is in the braking and turning zone of the track at the same time. If, between the braking forces and the turning forces, you overload the right-front tire, the car is going to push. Decreasing the crossweight reduces the static load on the right front and increases the load on the left front. Now, as the car enters the turn, the left-front tire provides more assistance in both braking and turning, which helps the car turn better. Overdo it, however, and you will make the car loose.
At The TrackLike most experienced racers, Spry uses weight placement to affect his left-side and rear weight percentages and depends on adjusting the ride height at the corners to dial in the wedge. "You don't change the left-side and rear percentages much after you get the car built," he says. "So once you get the lead placed you generally just leave it there. But I do change the crossweight a lot and change the way the chassis handles.
"You have to be careful, though, because you don't need to make much of a change to see a big difference. The most I ever turn the spring at once is one quarter of a turn. Since these cars only weigh 1,300 pounds with the driver, it doesn't require much of a change in terms of weight on the wheels to make a pretty big percentage change. On a 1,300-pound Legends Car a quarter turn usually equals a half-percent change in total crossweight."
Legends cars are known for having plenty of power but lacking traction. Because they race on short, tight tracks, Legends drivers are always working to increase forward bite, or traction at the rear wheels as they accelerate out of the turn.
"Passing always seems to be on turn exit," Spry continues. "There usually isn't much difficulty getting the cars into the turns, so guys can protect that inside line pretty well. It's on turn exit where the passing lanes open up, and the guy with the most forward bite is the one who usually gets it done."
On the bigger 31/48-mile tracks, Spry says he normally runs 48 to 50 percent crossweight because the car is better able to roll through the corners. But on the smaller quarter-mile tracks, the racing becomes more like a drag race down both straights. Because of that, he normally increases the crossweight to 51 percent in order to maximize forward bite. That, of course, is on asphalt. When racing dirt, the percentages are usually less because drivers like to break the rear end loose in order to make the car turn better.
So when you are at the track, don't think that just because you have maximized your left-side percentage and minimized your ride height that there is nothing else you can do when it comes to weight. Spry, who is one of the most successful Legends racers out there, says that crossweight is one of his favorite tuning tools. After all, making a crossweight change is quick, easy, and cheap (free as opposed to slapping on a new set of springs). Don't forget to take advantage of it to see if you can make your race car handle just a little bit better.