Photo by Brian Cleary, Grand Am Racing
Many well-known circle track drivers have tasted the wine-and-cheese circuit in all types of road racing cars. Tony Stewart drove a Daytona Prototype in the 2005 Rolex 24 at Daytona, and was leading with one hour to go when a part failed.
Ever since the Winston Cup boys started racing on road courses such as Riverside, California, and Watkins Glen, New York, some weekend circle track racers have desired to combine turning left with turning right. There is something intriguing and attractive about having 10 or 12 turns, all different, instead of basically two. So, we now have venues where a circle track racer can compete on road courses, sometimes with the same car.
Because vintage racing participation is growing and because so many of the Nextel Cup drivers as well as successful touring drivers are opting to drive on road courses in various series, we decided to address the setups for those cars as opposed to just turning left.
Ted Christopher, Northeast Modified champion, is shown here talking to the engineers durin
There are more than a few recognizable names who have driven in the 24 Hours of Daytona and other road races. These include Nextel Cup drivers Bobby and Terry Labonte, Kyle Petty, Tony Stewart, Rusty Wallace, Dale Earnhardt Jr. and Sr., and Kevin Harvick. More recently, Northeast Modified champion Ted Christopher has been added to the list. T.C. drove a Daytona Prototype for Doran Racing in the Grand Am Rolex 24 at Daytona race this year. The 2004 NASCAR Atlantic Regional Late Model Stock champion Steve Blackburn drove a Pontiac GTO in the Grand Am Cup division, a race that was run just prior to the 24-hour race also this year.
The most popular forms of stock car road racing today are the various vintage racing formats that allow older Busch and Winston/Nextel Cup cars to compete. The V8SCRRS, SARRC, and HSCRS are examples of vintage racing organizations that allow current and former circle track racers to compete. Even the Canadian CASCAR Super Series runs on the Mosport road course for one of its scheduled events. The popular Crown Royal IROC series will, for the first time, hold a road racing event at Daytona on June 29, 2006. As you might recall, that series invites championship racers from many different divisions to race together in a series of races, mostly on circle tracks.
Peculiarities of a Road Racing Stock CarIf we were to convert a circle track car into a road racing car, there are several areas of concern that must be addressed. Setting up a stock car for circle track racing is, in a number of ways, much easier than for road racing.
The front and rear suspension on this Spirit of Daytona Prototype is the double A-arm type
For circle track racing, we can set opposite cambers for the front and rear tires. We can adjust rear steer, crossweight (bite/wedge), and geometry to suit just turning left. For road racing, many of these same settings are a compromise, and that complicates things.
The issues and differences we need to address include: 1) front and rear camber settings, 2) front and rear geometry, 3) weight distribution, and 4) front and rear stagger (or lack thereof). Let's examine each particular area of setup and define how we approach them from a road racing perspective.
Since we will be turning left and right on road courses, we need to set negative camber (top of the tire leaning in toward the center of the car) in all of the wheels, front and rear. That means, of course, that the inside tires in each turn will be off camber and provide a lot less footprint than the outside tires, which have the proper negative camber.
This car has a coilover spring and shock combo, just like a Late Model that is connected t
The front tires are more prone to camber deficiencies than the rear tires, so we have a contributing factor in the car being tight, or understeering as the roadies call it. Therefore, the outside tire will be working harder to turn the car. Both front tires will probably need more camber than we would put in the car for a flat circle track, where the inside wheel is in positive camber and helping more so to turn the car.
A typical circle track car has positive left-front (LF) camber and negative right-front (RF) camber. In our conversion to road racing, we need to change the LF suspension to attain negative camber. We also need to make sure the control arms are the same length.
The effect is the same with the rear tires, but not to the same degree. We need to put more negative camber in those wheels from settings we know for circle track racing, because the outside tire is working harder.
The tire temperatures need to be read and set a little differently than normal oval racing requires, too. If the inside half of the inside tire is all that is working inside the turn, then that portion of the tire will heat up more and retain the heat when we have entered the pits and taken tire temperatures. Because we want to set cambers to benefit the footprint while the particular tire is acting as the outside tire, we should set the cambers so that we always read hot on the inside of each tire by 15 to 20 degrees.
Setting up a circle track car to be a road racing car is an art that requires you to under
At least 10 degrees of that difference is due to the extra work the inside half of the tire does while it is the inside tire of the axle pair. Tire wear will reinforce this method as well, but we still may see a slight bit of extra wear on the inside half of the tires. That is to be expected, and there is nothing we can do about it if we want optimum performance out of the tires.
The geometry of the front and rear needs to be tailored to the needs of turning both ways as well as other settings. For circle track racing, we have the liberty of using a moment center that is offset from centerline to enhance the dynamics. On the road courses, the moment center will have to be centered in the car.
The centering of the moment center must be combined with a geometry that allows the front dynamics to be the same for right and left turns. We also need to adjust our camber change characteristics so that there will be minimum camber change with the dive and roll we will see. If we are used to the dive and roll numbers from banked tracks, we might not have the best control arm angle settings for flat turns such as those experienced on road courses.
When the car dives and rolls in the turns, the moment center will move. If we start with the moment center at centerline at static ride height, then as it moves in the turns, it needs to move the same amount for a right or left turn. This keeps the dynamics consistent and the handling predictable for the different turns.
In this example, the moment center is moving in the opposite direction we normally see, but depending on the arm angles, this is a possibility. The design goal is to keep it near the centerline of the car in the turns and make sure it moves an equal distance for right and left turns.
At the rear, our trailing arm angles and the Panhard bar angle will need to be reset from what we are used to for circle track racing. We can manipulate rear steer in our cars for oval racing, but as said before about the moment center, our rear steer must be uniform for left and right turns.
The trailing arms should be set to the same angle on both sides of the car and level to the ground. The car will tend to rise less on the inside suspension and squat more on the outside suspension. If we have any angle in our trailing links, then this difference in travel of the forward ends of the trailing arms will produce some rear steer. If the links are angled upward and toward the front of the car, then the rear steer will be to the outside of the turn and produce a loose, or oversteering condition.
If the links are angled downward and toward the front, then the rear steer would be toward the inside of the turns and cause a tight, understeer condition. A level setting reduces rear steer in both directions and will produce a slight amount of rear steer to tighten the rear of the car. This gives the car better bite off the corner while not being so extreme as to make the car tight in the middle of the turns.
The Panhard bar should be level to the ground. This is not necessarily the optimum setting for all turns, but it is less detrimental to rear-end lateral movement, which can produce rear steer.
The height of the rear moment center is critical, too. As with oval racing, the car should be balanced front to rear, and the height of the rear moment center works in conjunction with the spring rates to accomplish the overall balance. With the stiff spring rates we will probably install, a lower rear moment center will probably work better.
Some cars have Watts' linkages for a rear location device. This system works well for road racing because it produces no lateral movement of the rear end as the car dives and rolls in the turns. The moment center height of this system remains consistent, making the dynamics more predictable and consistent.
Weight distribution is an often overlooked area of setup for the road racing car, no matter what classification-from Formula One to Mean Miatas. In circle track racing, we tune our setups with varying weight distribution numbers and read and record these as crossweight percentages or pounds of wedge/bite in the left rear (LR). Adding the RF and LR weights and dividing that number by the total vehicle weight (with driver and all weights) gives us the crossweight percentage. The amount of LR weight over the right-rear (RR) weight is referred to as "wedge" or "bite." For road racing, the crossweight and wedge must be zero or very close to zero, because the crossweight or wedge must be the same for turning in both directions. The car would handle differently each way, otherwise.
Every race car needs a certain weight distribution that is dependent on the front-to-rear weight distribution so that after weight transfer, the load distribution on the front matches the rear. For example, a typical Super Late Model car has a front-to-rear distribution of 51 percent, so 49 percent desires a 50/50 crossweight distribution (zero wedge) if the car is balanced dynamically.
The exact front-to-rear distribution for each car is dependent on the center of gravity height, unsprung weights, lateral g's experienced, and so forth. We cannot tell you what you need for your car, but if you have extra ballast weight to move around, moving it front to rear will definitely change the handling to help make the car more neutral.
Stagger in circle track racing works to help both tires turn the same number of revolutions through mid-turn, which helps the car to be more neutral in handling as power is applied coming off the turns. For road racing, we don't have that luxury anymore. Our tire sizes must be equal side-to-side at the front and especially at the rear. A turn to the left must be equal in all respects to a turn to the right for all kinematics and dynamics settings, and stagger is a part of that rule.
A typical circle track car has a crossweight that is above or below 50 percent. For exampl
Many road racing cars utilize special rear differentials that will slip to create a stagger effect. Tuning the degree of slip is an art unto itself, but that is nearly the only way we can adjust for no stagger. The front stagger must also be zero, but if a set of tires are not exactly equal in size, some stagger at the front will be less detrimental to handling (only affecting braking balance) than if we had it at the rear.
Tuning for Different Turns While we stated that all systems must be equal side to side, we will now move forward into fine-tuning the road racing setups by saying that some small differences are allowed in road racing. Every track will tend to have more turns in a certain direction than in the opposite irection.
A track that is run clockwise will necessarily have more degrees of turns to the right than the left, or we would never return to the start/finish line. In fact, on a track that runs clockwise, there will always be 360 more degrees of right turns than left turns.
The greater number of turns in a particular direction can affect our thinking on settings, but the average radius of each of the turns for the same direction is a consideration. For example, if we run a track with 12 turns, with 4 more right turns, we might be inclined to favor the right turns (as to cambers, and so on) to gain overall performance.
That may be a wise decision if not for the possibility of varying radii of the left and right turns. If our left turns are faster and longer and we can gain more speed in those than could be gained in the tighter right turns, then we should set up our cars to favor the left turns so that we will see more overall gain.
The crossweight for a road racing car needs to be 50 percent. That way, the handling balan
To do this, we would probably increase the RF camber, decrease the LF camber, introduce a small amount of rear steer to benefit left turns more (rear-end steering left for traction), and even alter the crossweight percentage to gain favor in the left turns if 50 percent crossweight distribution is a problem.
If you are preparing a former circle track car for road racing, start out with equal settings for both left and right turns. You cannot go wrong with that. Once you get used to that and get some experience and a feel for what the car is doing, try fine-tuning the car to favor the direction of turns where there might be a gain to be had. Oftentimes the handling will be a compromise, so we do the best we can and try to get the handling as close to neutral as possible.
Small improvements show a much greater gain in lap times on a road course than on a circle track. Where we might gain 0.20 second with an improvement on a circle track, the same improvement might gain 1 or 2 seconds on a road course. That is because there are two turns versus 10 or more turns. Don't forget the basics such as alignment, bumpsteer, and Ackermann steering effect. Good luck-you're a part of the wine-and-cheese crowd now.