The springs are the foundation of the setup. As Doug Arnao says, "the springs hold up the car". This may sound like a mundane function, but it's the heart of the setup. Together with ride height and differential, the spring rates determine the basic behavior of the car.
If the springs are too soft, the car will wallow around, and you'll have to run the car too high to keep it from bottoming the suspension. If the springs are too stiff, you'll give away grip, and the car will dance around over the bumps.
As I discuss in the appendix Spring Rates and Ride Height, these two setting choices go together. We can go either soft and high, stiff and low, or somewhere in between. Eventually we'll try to find the optimum compromise between spring rates and ride height for this particular chassis and circuit. However, we need to start somewhere.
Fortunately, I've done enough experimentation by now that I have a pretty good idea of what the various cars like on the road courses. Certain characteristics dictate different ride heights for the different cars, especially the three heavier cars. For the four lighter cars, I tend to run 70 or 75 lb./in. at the front, and set the rears in proportion to the car's weight distribution. This puts the rears in the 110 to 120 lb./in. range. The heavier cars will need proportionately higher spring rates.
For ride heights I start at about 3.75 inches front and rear on the lighter cars. This is high enough to keep the car off the bump rubbers at most circuits (except in a few special cases).
The BRM has to run higher, because of its weight and high center of gravity (which tends to make it roll and squat more) and because its natural ride height is higher than the other cars. The Murasama can get away with a little lower ride height because its natural ride height is lower.
See the Chassis Characteristics appendix for details about each particular chassis and refer to the Chassis Weights and Dimensions table for the cars' weights, weight distributions, and dimensions. Note that GRE has a built-in spring weight distribution calculator and shows each chassis' weight distributions.
For the shallower ovals, spring rates and ride heights will be about the same as for road courses. As the banking angle goes up, we need to run stiffer springs, and for the very steep ovals, higher ride height is in order too, because the download compresses the springs so much during cornering. GRE's extended ranges allow us to run springs stiff enough to keep the car up off the bump rubbers even at the monstrously banked (36°) Bristol.
Chris Moses taught me an important trick with the springs. On most ovals, the cars in GPL tend to overheat the right front tire after a few laps. This results in massive understeer and terrible lap times.
If you run a very soft left front spring and stiff springs on all the other corners, you can actually make the rear tires overheat and keep the right front cool. This, of course, results in oversteer, so you'll need to dial in the right amount of left front spring to get the balance where you like it. Generally if I'm seeing about the same temperatures on the right front and both rears, I figure I'm pretty close.
Incidentally, Chris tells me that real Champcar teams do the same thing, using soft left front springs to control understeer on ovals. I don't understand why this works. To me it's counter-intuitive. Increasing the stiffness of the outside front relative to the inside should transfer more weight away from the right front and to the left front. This should make the car tend to understeer more, so going softer on the left front to kill understeer is the the opposite of what I would expect. Don't ask me why, but it works.
The Salisbury differential fitted to GPL's cars is a very powerful setup adjustment. Its limited-slip characteristics exert a profound effect on the car's behavior. With everything else being equal, a change in the differential can make an oversteering car understeer, or a stable car unstable. If you don't thoroughly understand limited slip differentials, please read The Differential appendix.
The choice of ramp angles is a fundamental choice in a road racing setup. Probably the most common choice among GPL users for road courses is 85/30, which, combined with about 4 clutches, gives fairly forgiving behavior under acceleration (a smooth, controllable transition from mild neutral throttle understeer to power oversteer) and makes the car very stable under braking, which is a very important characteristic when the driver is trail braking. This is what I use. I've experimented with other settings, but I always wind up coming back to 85/30, with 4 clutches, give or take 1.
Many very fast drivers use ramp angles which are looser on the coast side, which makes the car less stable under braking. They are skilled enough, smooth enough, and have fast enough reactions to handle the car when the tail wants to go around. They also are likely make changes to the chassis to give it more basic understeer and more front brake bias.
I also know of drivers using 60 on the power side, but I can't imagine enjoying a car with this setting. Unless roll bar balance is set for massive understeer in steady state cornering, transition to power oversteer will be very abrupt. (Others disagree; see the Other Voices on the Differential page.)
For ovals, the equation changes. GPL's cars tend to understeer on steeply banked ovals. On the steep, high speed ovals like Michigan and Fontana, I use an open diff, 85/85 with one clutch (that's as near to open as we can get in GPL).
On the shallow ovals, I tend to start with an open diff, and once I find a basic balance with the suspension, I may add clutches and switch to a ramp angle with more locking on the coast side to stabilize the car in the corner entry phase. The additional clutches will also help get the power down.
If the preceding paragraphs make no sense to you, it's time to head on over to The Differential page. Once you've read that, come back here and reread this section. The differential is too important to go forward without understanding it.
The dampers (aka shock absorbers) dampen the motion of the wheels with respect to the chassis. The dampers affect the way the car behaves over irregularities in the track surface, such as bumps and dips. They also affect the way the car behaves in transient conditions.
In general, going stiffer on the dampers will make the car more nervous. Its responses to control inputs will be crisper, and it will react to the track surface more noticeably. Conversely, going softer on the dampers will make the car more compliant. It will tend to glide over bumps more smoothly.
However, if the dampers are too soft in bump, the suspension may bottom on its bump stops or the chassis may actually contact the track surface under momentary high loads. If they are too stiff in bump, the car will bounce from bump to bump.
Also, too little total damping may allow the chassis to bounce out of control if the driver touches a curb.
Dampers too stiff at the front may cause the front wheels to lock under braking; too stiff at the rear may cause the car to snap oversteer. Stiff dampers will also make the car over-react to touching curbs.
If the dampers are too stiff in rebound, the tires may not follow the track as well as they should when the car gets light. If the front dampers are too stiff in rebound at the front, the front end will tend to wash out when the chassis goes over a crest or a dropoff. If the rear dampers are too stiff, the car will have trouble putting the power down over bumps and other surface irregularities.
The dampers can be used to tune the way the car behaves in transient conditions, including braking and corner entry as well as accelerating out of the corner. See Transient States and Transient Responses for more details.
I typically use only the 2 or 3 click positions on road and street circuits. I find that 1 click is too limp to have much affect, while 4 and 5 clicks are so stiff that the car is too nervous.
Generally I use 2 clicks on bump and 3 on rebound at the front. This seems to give a good compromise between too stiff and too compliant. The car tracks nicely over the crown, and touching a curb won't unsettle it too much.
At the rear I use 2 or 3 clicks on bump and 3 on rebound, for the same reasons. If I want the car to be more responsive to throttle application, I'll use 3 clicks on bump; if I want it to be less responsive, I'll use two.
If I do run 3 clicks on bump, I may alter the roll stiffness balance a little to the front to give the car more basic understeer. This will result in a car that is more forgiving in corner entry, because if I make a sharp steering input the car will react only momentarily and then it will settle into a basic understeer state.
Some people use asymmetrical damper settings to tune the car's behavior to different corners on the circuit. I admit there may be potential here that I've left unexplored. See Transient States and Transient Responses for more.
On ovals I tend to run very soft dampers on the left front, sometimes as low as 1 click on bump and 1 on rebound, if I'm trying to dial out understeer. I start with 2 or 3 clicks on the right front, and 3 or 4 all around on the rears, depending on the steepness of the banking. The steeper the banking, the higher spring rates I'll be running, so the stiffer the dampers need to be.
If the car tends to snap sideways over the bumps and dropoffs in the entry of the corners on many of the ovals, I may go stiffer a click or two on bump on the right front. This will tend to wash out the front end a little when the car goes over these bumps/dips, and that helps to keep the tail from getting too far out of line.
Conventional wisdom says that you set tire pressures and camber by reading the tire temperatures. This is true only to an extent. Tire temps are a guide, but only a guide. You still need to use judgment and the stopwatch.
The rule of thumb I use is that the middle tire temp should be about the same as the average of the inside and outside edge temperatures. Increasing the pressure will increase the middle tire temp; decreasing it will decrease the tire temp.
I have tried many different tire pressures on GPL's road circuits. I've arrived at the conclusion that 20 psi all around is pretty close to optimal for road and street circuits, and for shallowly banked ovals as well.
I used to run 18 at the front and 22 at the rear. This has the advantage of making the car more forgiving at large slip angles - you can turn into the skid with less chance of the front tires' regaining enough grip to send you over the edge into a spin.
However, 22 is too hard for optimal grip, and 18 is too soft. Also, the increased spring rate of the rear tires means that the suspension will have to travel farther when you encounter a bump, and this increases the likelihood of bottoming the suspension, forcing you to run higher ride heights and/or spring rates, which increases weight transfer and gives away grip. Higher spring rates make the car more nervous, too.
Softer front tires also increase the likelihood of bottoming the suspension because of the resulting reduction in front roll resistance. Letting the car roll more increases the chances of the rear suspension bottoming.
I recommend starting at 20 psi all around. If you want to tweak from there, pay attention to the pressure of the tires after they get hot. On clockwise circuits, you may want to try running the right side tires a pound higher cold so that their hot pressures are closer to the left side tires. I don't think it pays to go too asymmetrical on tire pressures on road courses, though, because the car behaves too oddly when the tires are cold.
Shallow ovals load the tires about the same as road courses, so I start at 20 all around. I may go up on the left side by a pound or two to get the hot pressures closer to the right side's.
On steep ovals, I run somewhat higher tire pressures because the tires deform under the vertical load. They are more efficient at higher pressures because this results in an optimal tire contact patch when the download is high. On steep ovals, you really can't go for flat temperatures across the tread because the tire pressure will be too low in the corners, allowing the contact patch to distort, and reducing available grip.
I believe tire pressure is a key factor in setups for the moderately steep, fast ovals like Michigan and Fontana, and probably for the steeper ones like Atlanta and Charlotte as well. The trick is finding the right pressure for the given download. I think the only way to do this is by running a lot of laps, adjusting the pressures by a pound or two, and checking the stopwatch to see what's fastest. Start high, and work down, or start low, and work up. Lap times should fall as you approach the optimal settings, and will rise (get slower) as you go past them.
Note that left side pressures will probably be higher than the right, because they don't get as hot, but I usually run them only a pound or two higher than the right side.
Intermediate banked ovals like Gateway will fall somewhere between the two extremes. At Talladega, the banking is so steep that the car doesn't slide very much, so tire pressures seem to be less critical.
The camber affects the shape of the tire's contact patch, and its efficiency. Hold a pencil vertical to a desk with its eraser down, top of the eraser against the desk. Now push the pencil to the side. See how the edge on the opposite side lifts up? Now lean the pencil in the direction you're pushing it. See how the edge that lifted up sits back down? That's what camber does to a tire in a corner. It makes the tire sit flat against the track so it can generate maximum grip.
Conventional wisdom says you set camber by tire temperatures. Real-life tires are said to be happiest when the inside tire temperatures are about 10 to 15 degrees hotter on the inside edge of the tire than on the outside.
The tires in GPL aren't quite like this, however. They seem to work best when their inside and outside temps are about the same. The rule of thumb is that the more negative camber, the higher the inside tire temps will be.
Camber is something of a compromise on road and street courses. While adding camber can increase lateral grip, braking and acceleration in a straight line benefit from keeping the camber close to zero. For this reason I tend to run relatively low camber, and try to keep the chassis from rolling a lot by using fairly stiff anti-roll bars. This is how the real teams set their cars up in 1967.
I usually run .5 in. negative camber at the front and .25 in. negative camber at the rear. I typically run symmetrical camber at road courses, except at Monza, where I run zero or slightly positive camber at the right rear because there are only right-hand corners which are driven on the limit. Also, this helps reduce the understeer through Ascari.
Often the temperatures may seem to be telling you to run more negative camber, particularly on the left side. However, additional negative camber hurts straight-line braking because the tire works best in a straight line when it's flat to the track surface. It can also hurt traction under acceleration for the same reason. It may be better to bring the outside-edge tire temperatures down by stiffening the car overall in roll. This means going up a click or two on both front and rear anti-roll bars. I'll talk more about anti-roll bars under Finding the Balance.
Also, because most road courses are clockwise and have more right-hand turns, the tempuratures may seem to be telling you to run less negative camber or even positive camber on the right side. (Reverse this for Laguna Seca.) Beware of going too asymmetrical with camber on road courses, however, because this can make the car very unstable under braking. I ran asymmetrical camber on many setups for a long time, but now I've moved back to symmetrical camber almost everywhere except Monza.
Since you're only turning left on the ovals, you can run positive camber on the left side. I usually start at 1 in. positive on the left and 1 in. negative on the right. I run a few laps, adjust by the tire temps to even the inside and outside edge of each tire, and then run a few more laps. Typically I'll revisit this after making any significant change in spring rates or anti-roll bars, since this can change the amount of chassis roll.
The steeper the banking, the more camber will be needed, but only up to a point. On very steeply banked tracks, the G loads are so high that the chassis doesn't roll much. At Talladega where the corners are flat out and G forces are very high, camber seems to have less impact on tire temperatures, but I still keep an eye on them.
A small amount of toe-in at the front will tend to make the car turn in more gently; a small amount of toe-out at the front will make the car turn in more crisply. Once the car is loaded up in a corner, a small amount of front toe has little effect.
Toe-in at the rear has a small stabilizing effect because as weight transfers to an outside tire which is toed in and away from an inside tire which is also toed in, the additional steer angle causes the tire to exert slightly more lateral force. Running toe-out at the rear is a bad idea because it makes the car twitchy and unstable even on the straights.
Toe also has a small effect on tire temperatures; the leading edge will tend to heat up a little more. Toe-in will heat up the outside edge of the tire; toe-out will heat up the inside edge.
Running a lot of toe on a real car will tend to wear out the tires quickly, although this doesn't seem to be modeled in GPL. Lots of toe also increases friction and can impact straight line speed, although tests suggest that in GPL this effect is negligible.
I usually run about .05 in. of toe-in at the front and start at .075 at the rear. If the car is unstable, especially in mid-corner, I may add a little more, but I don't go over .200 for a road course.
It's fairly common practice to run negative toe at the front. I used to do this, but since I got a Force Feedback wheel, I don't like it. The car tends to turn in abruptly; in extreme cases, the steering wheel will "snatch" as I turn in, making it very difficult to point the car accurately at the apex. Toe-in tends to make the turn-in smoother and makes it much easier for me to point the car where I want it.
Some people are running very high toe values front and rear. I've seen as high as .275 toe-out at the front and .325 at the rear. A large amount of toe out will compensate to some degree for the fact that GPL does not model Ackerman effect. A large amount of rear toe in will stabilize a setup that is otherwise very unstable.
I've tried this but moved away from it after a few weeks. With FF, lots of front toe out makes the wheel "snatch" even more, and also drastically reduces the amount of feel that comes through the wheel. As for the rear, I prefer to make the car stable using other parameters which I feel are more appropriate. If GPL modeled tire wear, I'm sure no one would be running toe values higher than .200.
On the very fast ovals I run zero toe front and rear to eliminate as much drag from the tires as possible, even though I am pretty sure the drag produced by toe is minimal. But at high G loads small amounts of toe seem to have little effect on the car's handling.
On shallow ovals, I tend to use toe settings similar to those that I use on road courses.
The steering ratio is simply the ratio of turns of the steering wheel to steering movement of the front wheels. A higher number (18:1) gives slower steering. A lower number (14:1) gives faster steering.
Short, wide cars like the Ferrari and BRM need less steering lock than long, narrow ones like the Eagle and the Cooper.
The steering ratio you use is somewhat dependent on the type of controller you're using. I use a Logitech Force Feedback wheel which I've modified to have about 200° of travel lock to lock. I'll assume you've followed my advice and are using something similar. If you're using a joystick or some other device with less travel, you may need to use a slower steering ratio to make the car controllable. This has the drawback, though, of limiting the amount of lock available for hairpins and for recovery from excessive oversteer.
For most cars I use 15:1 everywhere. For the BRM and Ferrari, I go up a click or two to slow down the car's steering responses.
On short ovals, the same ratio I use on road courses is appropriate. For high speed ovals, it's appropriate to go up a couple of clicks to slow down the car's responses at high speeds, and to increase the degree of precision available.