Basic Principle: Get the back end to turn (just enough), and the front end to grip.
1) Toss the front roll bar away. If you need more front roll stiffness, stiffen the springs. You want to avoid unweighting the inside front tire at all costs. Both because it will spin (assuming that you're not running a LSD -- which is something that you'll need), and because you'll need as much traction as possible at the heavy end of the car. In a 911 it doesn't matter if the inside front lifts, in a FWD car it's guaranteed lap time death! Be careful not to overspring the front since this will just make it push more and lose grip on rough surfaces.
2) Whatever you have for front spring rate -- you'll need a lot more in the back. You'll also want a big sway bar. I've seen some early Honda Civics actually rig up 2 bars in parallel. I don't think that you really can have too much rear roll stiffness. Rather you'll just start to get deminishing returns.
3) Take a good look at your cage and how it attaches to the suspension system. Torsional stiffness is critical since you'll constantly be using the rear suspension roll stiffness to prop up the front end.
4) Lowering the car (without distorting the geometry) will make a big difference in so much as it reduces the weight transfer. Some guys just forget about any geometry issues and slam the car on the ground which lowers the front roll center significantly and increases the front end's tendency to roll. They make up for this by cranking in a lot of static camber and huge springs. The strategy is as spelled out in my signature.
5) Take a close look at your front geometry. Most FWD cars have MacPherson Strut front suspension which tends to lose camber in roll. Adding Caster can add a lot of this camber back. Within reason it doesn't hurt the steering effort much since the front wheels are pulling the car, so if this change results in any "steering trail" you'll wind up with the tire patch pushing the steering axis as opposed to RWD cars where the contact patch is dragging behind the steering axis (like a grocery cart). Keep in mind that you will lose some self-centering action by making this change.
6) A small amount of rear toe-out can often help the car to rotate. How much depends on the track and how high speed the corners are. If there are a lot of sweepers, then no toe-out may be better. For auto-x, more will most likely be better. By the same token, some guys run narrower tires on the back then on the front. As you mentioned, the rear tires aren't doing much anyhow. Making sure that you have maximum track width on the back end is also important.
7) Don't be shy about considering asymetrical set-ups. At LRP ( 5 out of 6 corners are to the right), I would generally take some load off of the left front by removing some shims. Basically this transfers load to the RF and LR tires. In 5 of 6 corners both of those tires were nowhere near as stressed as the outside front tire.
Cool Finally don't forget the shocks. It's really important that you have your shocks valved to match your springs. Some objectives:
A) Dampen the stiff spring rates. FWD cars can get a really funny/scary oscellation that alternates from the front to the rear. It used to be a big problem when the BTCC started to use FWD cars until they got a handle on it. I occasionally ran into it with my Mazda 323 and the first few times you experience it, it can be plenty scary. It doesn't throw the car off the track or anything so all that you need to do is grit your teeth and drive through it. I never got around to spending the money on shocks to fix it in my case, but oscellation problems generally require a shock fix.
B) You don't want a lot of rebound dampening in the front, once again to keep both tires on the ground.
1) Toss the front roll bar away. If you need more front roll stiffness, stiffen the springs. You want to avoid unweighting the inside front tire at all costs. Both because it will spin (assuming that you're not running a LSD -- which is something that you'll need), and because you'll need as much traction as possible at the heavy end of the car. In a 911 it doesn't matter if the inside front lifts, in a FWD car it's guaranteed lap time death! Be careful not to overspring the front since this will just make it push more and lose grip on rough surfaces.
2) Whatever you have for front spring rate -- you'll need a lot more in the back. You'll also want a big sway bar. I've seen some early Honda Civics actually rig up 2 bars in parallel. I don't think that you really can have too much rear roll stiffness. Rather you'll just start to get deminishing returns.
3) Take a good look at your cage and how it attaches to the suspension system. Torsional stiffness is critical since you'll constantly be using the rear suspension roll stiffness to prop up the front end.
4) Lowering the car (without distorting the geometry) will make a big difference in so much as it reduces the weight transfer. Some guys just forget about any geometry issues and slam the car on the ground which lowers the front roll center significantly and increases the front end's tendency to roll. They make up for this by cranking in a lot of static camber and huge springs. The strategy is as spelled out in my signature.
5) Take a close look at your front geometry. Most FWD cars have MacPherson Strut front suspension which tends to lose camber in roll. Adding Caster can add a lot of this camber back. Within reason it doesn't hurt the steering effort much since the front wheels are pulling the car, so if this change results in any "steering trail" you'll wind up with the tire patch pushing the steering axis as opposed to RWD cars where the contact patch is dragging behind the steering axis (like a grocery cart). Keep in mind that you will lose some self-centering action by making this change.
6) A small amount of rear toe-out can often help the car to rotate. How much depends on the track and how high speed the corners are. If there are a lot of sweepers, then no toe-out may be better. For auto-x, more will most likely be better. By the same token, some guys run narrower tires on the back then on the front. As you mentioned, the rear tires aren't doing much anyhow. Making sure that you have maximum track width on the back end is also important.
7) Don't be shy about considering asymetrical set-ups. At LRP ( 5 out of 6 corners are to the right), I would generally take some load off of the left front by removing some shims. Basically this transfers load to the RF and LR tires. In 5 of 6 corners both of those tires were nowhere near as stressed as the outside front tire.
Cool Finally don't forget the shocks. It's really important that you have your shocks valved to match your springs. Some objectives:
A) Dampen the stiff spring rates. FWD cars can get a really funny/scary oscellation that alternates from the front to the rear. It used to be a big problem when the BTCC started to use FWD cars until they got a handle on it. I occasionally ran into it with my Mazda 323 and the first few times you experience it, it can be plenty scary. It doesn't throw the car off the track or anything so all that you need to do is grit your teeth and drive through it. I never got around to spending the money on shocks to fix it in my case, but oscellation problems generally require a shock fix.
B) You don't want a lot of rebound dampening in the front, once again to keep both tires on the ground.
(i "spun it" on our kart track 3 times on 1 lap the other day :wasntme
