Whats your car doing on the turn entrance and in the middle?
Whats your car doing on the turn exit?
Boris Said at the Ford LA Street Race.
At Sears Point, Said considers Turn 10 (the horseshoe-shaped corner at the bottom of the p
Caster settings can change the amount of crossweight on a car. The evidence can be found o
Springs, shocks, brakes, sway bars, track barsyou name it, its important.
Production cars converted to sports car racers (like BMWs, Mazdas, and GM F-body cars) oft
Quick fact: The LA Street Race is NASCARs only street race. Its run near downt
While road course setups vary significantly from oval configurations, the laws of physics and the application of hardware remain similar. Obviously, the main difference comes from tuning with a left-side weight and suspension bias (oval), compared to a neutral setup configured for multiple types of corners (road course). Between both disciplines of racing, the symptoms of handling remain similar, too; just the initial point of reference differs. For those reasons, this story can be useful for oval racers as well. Road course naysayers, save your hate mail and subscription cancellations for somebody whos not trying to expand the way you think about a race car.
At the most basic level, each road course turn can be dissected into an entry, a middle, and an exit. Dissecting a corner into those elements and analyzing the cars performance is the key to going fasterjust like on an oval. Dont confuse going fast with scaring the bejesus out of yourself at every corner, either. As road course racers quickly find out, a smooth, steady, calculated, fast pace throughout the entire course results in better lap times. The abusive treatment of throttle and brakes just wear out the car faster. The scariest part of going fast is doing it in a car thats not set up properly. When setting up a road course chassis, the goal is to achieve the most traction where it will benefit lap times and passing the most. That means compromise.
Circle Track consulted a variety of sources for this story, including road course ace Boris Said of Carlsbad, California. We also spoke with Ed Ash of Umpqua, Oregon, who owns Ash Racing Engines. Hes much more than a respected Ford engine builder. His road course experience includes building Trans Am cars from the late 70s through the late 80s, building Stock Cars for ovals and road courses, and consulting NASCAR Touring Series teams on how to convert an oval Stock Car to a road course car. Hes a Swiss Army Knife for race cars. His son, Brandon Ash, races in the NASCAR Featherlite Southwest Series and the Winston West Series.
At the minimum level, the information in this story applies to production-based sports cars with narrow tires and a relatively large amount of suspension travel. At the maximum level, any NASCAR-style Stock Car racers might find some of the information useful, too. Cars with very little suspension travel, big, 13-inch-wide tires, and significant aerodynamic downforce (like a modern BFGoodrich Trans Am Series racer) will typically follow more unique setup guidelines.
Analyzing the Track
Since a car can only have one setup and a road course typically has around 10 to 15 turns, the approach to chassis setup should revolve around the most important corner. But what is the most important corner, anyway? According to Said, it is often the one that leads to the longest straightaway with the best passing opportunity. Of course, setting up a car for the most important corner doesnt mean ignoring the rest of the track, either. Its a compromise between having a setup that behaves as well as possible throughout the whole of the course, but places emphasis on making the car perform where its realistically possible to make gains. With this approach, Said often finds that he is extremely fast in a few corners, good in a few more, and taking it easy in the bad corners.
You need to know where to go slow to go fast, says Said. The conditions of the track and its surface texture are also important factors. A smooth track without bumps will allow the car to be sprung stiffer. Also, concrete surfaces often provide better grip than asphalt, and asphalt can get greasy on blistering hot days. Street courses often present the obstacle of mixing asphalt and concrete surfaces. The bottom line: Be acutely aware of changing traction factors and adjust your driving style appropriately.
Cornering Problems and Common Solutions
Springs, antisway bars, and track bars provide significant tuning opportunities. Changing any one of those components can drastically affect understeer (push) and oversteer (loose). As mentioned earlier, separating a corner into three segments (entrance, middle, and exit) provides three important reference points to analyze what the suspension is doing. For example, a car can be loose in certain parts of the corner and neutral or tight in other parts. Racers like Said and Ash tune for good forward bite combined with an overall neutral feel. When Said determines suspension changes, he often goes by these accepted rules of thumb on road courses:
If the car is tight overall, try using a softer front antisway bar, stiffer rear springs, raising the track bar, using softer front springs, or a combination of them all.
If the car is loose going into the corner, use a stiffer front antisway bar, a softer rear sway bar, lower the track bar, or a combination of these solutions. If the car is loose exiting the corner, use a stiffer front antisway bar, softer rear springs, or a combination of the two.
In Winston Cup cars, Said often changes the antisway bar two sizes at a time so the changes can really be felt (i.e. from a 1-inch bar to a 13/16-inch bar). If the change feels too drastic, he can always go down one size.
An antisway bar behaves much like a progressive spring. Ash explains that, in
theory, an antisway bar (front or back) should accent the outside tire in the middle of the corner. When its right, it will help provide forward bite as the car starts to exit the corner. He cautions against using stiffer springs in the rear when a stiffer antisway bar is really needed. He says the stiffer springs dont help provide as much forward bite, and braking could suffer.
A good road racer decelerates with the brakes and the engine to prevent the cars attitude, or balance, from changing drastically upon entering a corner. If a driver says the brakes are too good, then you have the wrong driver, explains Ash.
Brakes equal horsepower on a road course. On a car with a solid rear axle, axle hop is a major concern. Ash considers front/rear brake bias and shock selection to be two ways to control wheel hop. In the brake bias department, more front-brake bias can help solve the problem. In the shock selection department, a shock with a stiffer rebound setting can help control wheelhop, too. Ash wouldnt consider using a shock with 50/50 rebound and compression for a road course. He prefers rear shock with a stiffer rebound setting.
Also, test the car with a light fuel load because the weight difference (sometimes in the neighborhood of 150 pounds) can affect wheelhop as well. Wheelhop is less likely on production-based sports cars with an independent rear suspension because the center- section of the axle is hung by the chassis, but it can still occurespecially if an unskilled driver is punching the the brakes and shifting the gears.
Camber, Caster, and Toe
From a handling standpoint, camber, caster, and toe affect the perceived balance of the car (and the actual performance). As you probably already know, camber describes the inward or outward tilt of the wheels. When wheels tilt inward at the top, they have negative camber. When wheels tilt outward at the top, they have positive camber. The front wheels on most race cars have negative camber, but not always at a symmetrical angle. Camber also depends on a cars particular type of suspension design and the track, so generalities are few. The goal for tuning with camber is to maximize the contact patch of the tire in relation to the changing geometry of the suspension when the car is cornering.
Caster describes the angle that the front wheels create when turned. Although people disagree about the effects of caster as a good thing, Ash believes positive caster adds desirable crossweight when turning into a corner. When the car is on a set of scales, turn the wheels to the right and left to see how the diagonal crossweight changes on cars with a lot of positive caster.
On a Southwest Tour car at Sears Point, for example, Ash will run about four degrees negative camber on the left, three degrees negative camber on the right, and about five degrees positive caster on both wheels. Unfortunately, there is no such thing as perfect camber on a road course. A gain in one turn can cause a loss in a different turn. The best approach is to analyze the race track and have good driver feedback. Also monitor tire temps on the outside, middle, and inside; and inspect tires closely for uneven wear. However, tire temperatures should not always be considered gospel, because they may not be representative of the entire course and can change by the time the car gets in the pits and is parked.
Toe-in and toe-out describe the front wheels inclination to be pointed slightly toward each other or slightly away. Toe-in occurs when the front of the tires point in toward each other; toe-out occurs when the front of the wheels point away from the car. Street cars with front-wheel-drive typically are set with toe-out because the wheels tend to pull toward each other under acceleration. Rear wheel drive street cars are typically designed with toe-in because the leading edge of the front wheels tend to push away from each other. Rear wheel drive race cars are different though. Ash considers a slight amount of toe-out gives the driver more feel, a slight amount of toe-in gives the driver less feel. By slight, he means an adjustment out of center by 0.020 or 0.030 of an inch. Excessive toe-out will scrub away tires and scrub away speed.