The Quest to fit 10 Inch Wide Rims on the front.!

**GTOJOE** · 02-22-2011, 08:33 AM

Thicker sway bar in the rear?

**GTOJOE** · 02-22-2011, 08:42 AM

Originally Posted by inperfectdarkness

one thing i DID learn from that link though (thx, btw) is that the stock tire combos have 1" upsize on the rims to the tires. 8" wide rims use 9" wide tires. 8.5" rims use 9.5" tires. (approximately on all of these).

That's because wheels are measured from the inside lip to the other inside lip while tyres are measure from the outer sidewall to the other outer sidewall.

DG · 02-22-2011, 09:18 AM

Thicker sway bar in the rear?

Doesn't work - well, doesn't work as expected.

The thicker rear sway bar attempts to reduce grip on the rear by increasing the amount of rear weight transfer. Normally, that increases oversteer.

But AWD cars have a differential connecting the front and rear wheels. When you apply power, the differential "senses" (that's a gross oversimplification of a complex action but we can treat it this way) that the rear has less grip and routes the power forward - where it induces understeer.

However, that rear sway bar is still there, doing it's best to unstick the rear. So in instances where the differential isn't playing games, it induces oversteer.

What you wind up with is a car that, in the main, understeers, but every once and a while snap-oversteers with very little warning - and the more rear spring/bar you put in it, the worse it gets.

The 3S has a rear-torque-bias centre diff so the problem should be a little less prevalent, and indeed, the 3S will rotate a little with throttle before the understeer takes over. But any car that can sent large amounts of power forward will understeer.

I set up AWD race cars with just the slightest bit of spring/bar oversteer bias, so you can get the rear dancing on rapid transitions and lift throttle, and I prefer to do it with spring rather than bar (after a series of aftermarket rear bars, I eventually went back to a OEM rear bar) The 3S, with it's rear-torque-bias centre diff, probably needs even less rear spring.

The other issue here is that the 3S has McStruts on the front, so it has horrible (which is to say, very little) camber gain in roll. The way you normally combat this is to run a lot of front bar, and I expect that a good way to reduce understeer on a 3S is to thicken up the front bar a lot.

However, once you get to the point where you are lifting the inside front clear of the ground - normally the hot ticket on a car like an M3 or Mustang - that differential issue rears up. Lifting the inside front under power is going to cause all three diffs to go insane.

So on a 3S... well, the main issue with a 3S is "doctor, it hurts when I do this" so the solution is to "don't do that" and get a car with less Weird Harolds (like a C5 Corvette) for track use. But if you are bound and determined to use the 3S, the answer is probably more front bar, as the lack of camber gain in the front is the single largest problem. Quaife front diff, Quaife centre diff (assuming that doesn't remove the rear torque bias feature, which is pretty important) and leave the rear viscous.

Street car, larger front bar and be done with it.

DG

**MR2** · 02-22-2011, 02:33 PM

Originally Posted by DG

It won't.

Understeer/oversteer is a measure of the balance of the grip on the car. A car that understeers loses grip on the front first. A car that oversteers loses grip on the rear first.

By fitting wider tires, you (in theory) raise the limits of the car, meaning that the point where the car loses grip will be higher up than it was before. But the ratio of when it loses grip will be unchanged.

In order to change the understeer/oversteer balance via changing tire widths, you will have to run wider tires on the front than on the rear. Because the understeer in the car is largely built in (due to AWD and weight distribution) to make any real difference in understeer/oversteer balance through tire widths will require the fronts to be very much wider than the rears - like 285s on the front and 235s on the rear.

I tried something like that on my race car, early on (235s on the front, 205s on the rear, in a BFG R1 race compound) and it worked in some situations, but it also limited the maximum amount of grip in the rear and there were times when I needed more absolute grip out of the rears, so I abandoned the experiment.

90% of the understeer complaints I see are driver induced and cannot be fixed via mechanical means. Go ahead and fit super-wide tires on the front if you wish, but be aware that it will not cure your understeer issue.

DG

sorry, I'm obviously not being clear...by "I figure it will help" I don't mean with the balance, I mean with the overall performance of the car.