Quote:
Originally Posted by gimp  Enter the turn slower.
I'm not being rude by any means, but I want to give the right advice. How much track time/autocross time do you have? |
Gimp brings up a valid point. You can gain lots of time by getting on the brakes a little sooner, staying tight on your apex cone and getting on the throttle earlier. Also, make sure you finish braking before you begin turning. That is also a surefire way to induce plowing.
Assuming your driving technique is okay, here's my suggestions:
First, take the front struts off of full stiff. This will help remove understeer at turn in. Too stiff of front shocks will cause the weight transfer to happen very quickly, causing the outside tire to lose grip and slide. I would go closer to full soft than full hard, but somewhere close to the middle is probably okay for now. I would also take the rears down closer to the middle as well.
Check your front sway bar for bind. After putting an aftermarket sway bar on my car, it began pushing terribly! Turns out that most of the aftermarket bushings that are used to mount the sway bar to the body are too large and will prohibit the sway bar from rotating as it should. The best way to check this is to remove the endlinks from the sway bar (or disconnect the end links from the control arms) on both sides and see if you can easily rotate the sway bar. Think 1 finger's worth of effort. If it is harder than this, you probably need to lubricate the bushings and possibly shim the brackets that hold the bushings + sway bar to the chassis.
Get more negative front camber. Unless you are above -3 degrees, more will help. With the grippier tires, the car's body will roll more, necessitating more camber. Shims/washers are the cheap way to do it, but you might run into some fitment issues depending on how much you dial in and the offset of the rims. With your wheel/tire sizes, you should be fine. Camber plates are the better and more expensive option. -3 degrees may seem like too much, but with the suspension on the front of these cars (macpherson strut) you don't gain as much camber in compression as you lose due to the body roll. As a point of reference, the Vorshlag guys were running around -4 degrees on their e30 ST car.
Check to make sure the car isn't riding on the bump stops or going to coil bind during cornering. If you are hitting the bump stops in the front, your effective spring rate is skyrocketing, overloading the front outside tire and causing it to lose grip and slide. There are a couple ways to check this. You can attach a zip tie to the shaft of the front shock and see if it move upward into the bump stop. Since bilstein probably did an okay job designing the kit, you should have to worry about the springs going to coil bind, but just to make sure, you can put a small piece of sticky-tack on one of the middle coils. If the piece gets compressed to where the layer on top of the coil is essential see through, you know the two coils must have touched at some point. Synopsis: If your front is super low, you may very well be riding on the bump stops during cornering. Either raise the front of the car some, cut the stops down some, or some combination of both. Just don't remove the bump stops all together. You need the protection they provide.
Tire pressures can also have a significant effect on car handling. I run slighly (about 3psi) more pressure in the front tires due to the higher weight over the front axle. Too much front pressure can cause understeer. Too low on the front pressure and you'll see the tire being scrubbed over on the sidewall. You want to find the lowest pressure that keeps the tire from scrubbing down too far. Optimizing camber will help in that regard. I run my 205/45/16 b-stone re-01's at 35-36 front 32-33 rear. Too little in the front and it starts to feel mushy. Too much in the front and it loses grip. Different tires like different pressures. Do some experimenting to find out. Tire pyrometers can be a big help here, but you should be able to get close without one. You can increase the rear pressure some to help the car rotate better, but the downside to this is that you lose some forward bite. If you don't have any wheel spin issues on corner exit, this might be something to try if the above suggestions don't work. Assuming you don't have a limited slip differential, this is probably not a compromise you want to make.
I suspect addressing those issues will help significantly. If it is still more pushy than you would like a stiffer front sway bar may help. Typically more front roll stiffness (what a larger front sway bar gives you) will increase the understeer effect, however, it will reduce total body roll, which reduces the amount of camber the front tires lose, which means more front grip. Clearly there's a trade off here. At some point further increasing the front sway bar size will induce more oversteer. I'm running a 28mm eibach bar at the softer setting. Body roll is much better, but it still exists.
What to do with the rear sway bar is a bit of a loaded question. I think the right answer depends on a multitude of other parameters, such as driving style, tire grip, springs and stocks, front bar, and differential. I run the eibach rear bar set on full soft. It's great on grippier surfaces, but on slicker asphalt lots, it doesn't give as much rotation as I'd like. I probably need to go up a set of holes on that surface. The problem with a stiffer bar and to some extent any rear sway bar in general is that it limits the abilty of the inner rear spring to plant the inside rear tire. When you have lots of grip (ie race tire) the tire is hardly touching the ground at all, causing excessive wheel spin when you get back on the throttle at the exit of the corner. Removing or softening the rear sway bar helps to better plant that tire (or at least keeps it from being pulled up as much). If you're not having wheel spin on corner exit problems, a stiffer rear sway bar might be a good way to help with rotation. Without a limited slip, increasing it may cause more trouble than it's worth.
And please, whatever you do, don't put the old tires on the back to try to improve balance. That is throwing away grip! Figure out a way to make those puppies do more work!
My 0.02, YMMV, use at your own risk, etc...
Apologies for being so long winded. I hope this helps!