Wearing out tire shoulders

#1

I am cording tires about 1"-1.5" in from the outside tire edge way before the thread is worn down below the groove. (yes even with tire rotate and flip.)

I am looking for ways to make the tire wear more even. I have -2.9 and -2.8 front camber and -2.2 and -3.0 rear camber. The front camber is maxed out with the current set up.

Because I use stock sway bars, I have good amount of body roll in turns and I suspect that might be changing the effective camber.

I am considering either;

  1. Get a better camber plates to add maybe another 1/2 degree to the front camber.

or

  1. Get a set of sway bars to lessen the body roll.

Tires are expensive and any advice would be appreciated to make them last longer.

TIA.

#2

Beefier sway bars will help correct the tire’s contact patch geometry while in a turn. Your front camber is a little low but still reasonable for your SpecE30 cousins. My perception is that OEM sways are too weak for the track. If you put on beefier sways, you might also reinforce the sway bar attachment points, if not done already.

Additional front neg camber will help, don’t get me wrong. But I think that the biggest problem is the weak OEM sways. I’d fix that first.

-3.0 is a lot for rear camber. Might want to experiment with 0.5 to 1.0 less then front. Like -2.8F and -2.3R.

#3

What’s the front toe set to?

#4

Chi - what pressures are you running? Have you taken any tire temps?

#5

Slight toe in at -.06 and -.04 (I think that’s about 1/32)

Cold pressure at 31-33 depending on the corner. Usually end up around 38ish after a cool down lap.

I don’t have a way to measure temperature so I don’t know.

I have decided to try RD 22/19 sway bars and see if that will help. If not, I am going to borrow a set of better camber plates to see if I can add more camber.

#6

Pressures sound about right. Maybe be the bars will help. We run 1/16 to 1/8 total toe out up front.
Ed

#7

Don’t quote me on these data but here is some info on Racing Dynamics 22/19 mm sway bar rate calculated using this calculator.

Stock Front 20mm = 606 lbs/in

RD Front 22mm Outside = 888; Middle = 1260; Inside = 1756 lbs/in

Stock Rear 12mm = 52 lbs/in M3 Rear 14.5mm = 110 lbs/in

RD Rear 19mm Outside = 326; Inside = 402 lbs/in

I could not find the motion ratio for E30 sway bar connection points. Does anyone know?

#8

Just came back from CMP where I got to try out the new RD sway bars. The tire wear is much better now. It follows the curve of the tire and does not eat into the shoulder area.

In the picture, left side is with the new RD sway bars and the right side is with stock sway bars. No change is alignment or tire pressure settings.

The only down side is that I have lost the fine balance I had with the stock sway bars. The car now pushes a bit and fairly hard to get the back end to rotate. I will have to try playing around with the bar settings next.

#9

Was the new behavior in right, left turns or both?

If you camber settings are unchanged, that could explain the “pushes the bit and fairly hard to get the back end to rotate”. At least as far as your right side goes. Left side seems pretty good. An eccentric RTAB would fix that right side up.