FRporscheman

The problem is on my '93 968. When I bought the car, it was fine. Recently it's had this issue where the inside shoulders of my front tires keep wearing out. I adjusted the camber eccentrics to maximum positive camber a few months ago, and it's still wearing out the inside shoulders.

The only change that I can think of is the fact that I put on a pair of 951 front struts with lowering springs. I did not install any kind of geometry correction (so yes, I have annoying bump steer). But, shouldn't lowering the car create more positive camber, not negative? My tire wear indicates too much negative camber, right?

The wheels are 17x7 et55 and the tires are 225/45/17, as stock.

With the eccentrics maxed out and the lowering springs, I don't know what could be causing this. Does caster affect camber? I.e. can an alignment shop fix this, or is there something wrong with the car?

Butters944

Lowering a car makes camber more negative, naturally.

http://www.spcalignment.com/faq/arti...vehicle_height



Negative camber:





Positive camber:

car_slave

What most likely happened is that when you lowered your car you increased the toe-in. Have the front alignment reset to factory specs, or get some camber plates and do it yourself. Normally you want about an 1/8 to a 1/4 of toe-in Total with the toe plates. I'll bet you have more than that.

harveyf

I agree with Butters that lowering your car increases negative camber. But surprisingly the effect is pretty minimal. See my post at www.newhillgarage.com.

I lowered by track car by 1" and have introduced maximum negative camber as allowed by the stock eccentric bolts, which gives me about neg 2 degree. After about 6 track days on basically new tires, I don't have any noticeable wear on the inside versus the outside or the middle.

If you want to experiment a little and not wait for $400 in tires to wear funny, try using chalk or white shoe polish to draw "stripes" starting at one sidewall, across the tread, and down on the opposite sidewall. Drive around a little and see if the stripes are removed an even amount from the inside and outside sidewall. This will allow you to get a quick read on any alignment changes.

Set castor first, then camber, and then toe in.

NCporsche

In regards to remembering positive camber and caster. Think of OUTBACK steakhouse as POSITIVE.

POSITIVE camber is OUT (top of tire), POSITIVE caster is BACK (in relation to axle) .

A chopped motorcycle has a lot of negative caster.

FRporscheman

Hmmm. I thought the control arms' natural position was horizontal. So that's why I thought lowering (or raising) would make camber more positive. But if the CA position is like the picture at normal ride height then I understand how camber will become more negative with lowering, until the CA becomes horizontal, then become less negative until it reaches the same camber as originally when the CA is at an angle mirroring the original angle. Am I understanding this right?

So I either need a geometry correction kit, or camber plates?

Either way it'll need an alignment when I figure out how to get 0 camber again. The caster and toe are probably off too.

MAGK944

You are correct, that drawing is a bit missleading. The arms start out almost level with stock camber a little negative. As you corner the arms point up at the ball joint and cause the wheel to become neutral or if you like more positive.

If you think about it that is exactly what should happen. It is desirable to have an alignment that causes the tires to have maximum contact with the road in turns and that means you need a slightly negative camber in the straight ahead position. At least on our cars anyway.

Lowering your car will make the arm point up at the ball joint instead of being level. In that position the stock ride height car will have positive camber but you need to dial in negative so when you corner you go more neutral or positive. Problem is you don't have enough adjustment at the eccentric to dial in enough of you go to low.

Best solution would be camber plates. I would also consider the geometry correcting arm pins to bring everything in line (level) again and prevent your ball joint binding and cracking your arm.

Hope that makes sense. GL

NCporsche

Talking about caster, not camber, caster has no effect on tire wear. Caster has more to do with return-ability of the steering wheel after a turn. You should have some negative caster so when accelerating the tire remains ahead of the axle giving it more stability.

MAGK944

Who's talking about castor? He has a camber problem here, though you are right in what you are saying

FRporscheman

Thanks Mike, that does make sense. That's how I thought things were.

But I'm still at a loss for what is causing the inside shoulder wear on my front tires. I'm not saying it's not the lowering springs, but if it is, then I'd like to fully understand why, because right now I think the springs would make the outsides wear more, if anything.

krystar

camber doesn't wear tires. camber only affects WHERE the tires wear more.

toe wears tires.

mytrplseven

Just out of curiosity, where's the camber specs for an '87 944 NA? I just replaced the front struts and put the concentric nuts close to where they were when I pulled them. I've driven the car a little to settle things in and the Porsche shop says they need to do a complete realignment of the front? True? Or just camber check?

NCporsche

Per the previous post by mytrplseven

My '86 944 is going on the alignment rack Monday. I'll be aligning her myself.

My shop manuals are at the shop and I'll post Monday evening what the specs are and what can be aligned, front and rear, camber, caster, toe, possibly ride height.

I do remember the alignment is supposed to be done with a full tank of gas.

xsboost90

when you lowered the car you toed the front end OUT- there for its dragging the inside of the tires- get an alignment.