Brett Jenkins

I had another alignment when I had these new tires mounted <5k miles ago. I made sure the shop had the correct equipment and knowledge, they had aligned 928's before. The specs turned out as follows
LF Camber -.6 RF Camber -.4 LR Camber -.7 RR Camber -.6
Caster 3.5 Caster 4.3
Toe .11 Toe .15 Toe .13 Toe .13

Front Total Toe .26 Rear Total Toe .26

Front Steer Ahead -.02 Rear Thrust Angle 0.00

My problem is that the RF tire is completely worn on the inside. I thought at first it was my less than ideal offset on my 993 wheels, but it's only wearing the RF wheel, the LF looks normal.

I've attached a picture of the two tires. Should I have the alignment re-checked to see if it's out of whack or are there other explanations for this?

Replacing tires at 5k miles is getting expensive.

Mrmerlin

Brett what is the ride height set at??
If its not close to factory then your going to have raise the front end up some so the rack pivots are closer to the a flat plane, the further the front end is dropped the more out of alignment thing will get when the car is moving up and down

Brett Jenkins

Hmm, excellent question. I'll check.

WallyP

Brett,

Did you actually watch the whole procedure? That is, are you absolutely certain that the car was not lifted before or during the the entire procedure?

Mrmerlin

have seen this situation a few times.
On the alignment rack everything is great once it leaves then the tires are wearing out on the inside in less than 3k miles,
Remedy raise the front end to return the steering geometry to factory specs.

Imo000

Or crank the right outter tie rod in a turn or two. Mine looked like that after chanig the right outter tie rod and only aligning it by eye.

GregBBRD

Or install a "bumpsteer kit" to lower the tierods....

mark kibort

It's toed out, and the alignment you got isnt worth 50 cents.

Do the toe yourself. As was offered, turn each tie rod in 2 turns, BUT, make sure you turn EACH tie rod a couple of turns, not one.

better to measure the toe yourself, as Ive outlined in many posts. all you need is a level and a magic marker, (and a measuring tape). make a mark off the tire, rim to the ground, front and rear of the tire. the two marks for the fronts should be narrower than the rear marks by about 1/8" .

just for giggles, see what you have your alignment is set at. you can save those tires by rotating them to the rear, if they dont look too bad for your liking.

mark kibort

This is plain not true. I run race rubber for 40,000miles and 8 full years of racing, , 125 race days, on this one chassis, and never had any issues like this at all. if you dont have a good alignment, you will wear the inside edge. all the bump steer BS in the world wont cause this. The ONLY thing bump steer issues do, is on high g loading turns, to make the full droop tire scrub a little, but its usually only on the race track and its very mimimal, as to do this, there is not much weight on that wheel.

I run the front end of my car at 110mm, so I think you dont have an issue If my tires wear perfectly even, even racing on DOT race rubber!

mk

Brett Jenkins

I did watch the alignment to make sure it was not lifted and that it was drawn down. I can't swap front to back, since they are different sizes.

I will manually check toe first chance i get.

On another note, when i bought the car, it had factory 16" d90's. I drove it home and put on the 18" wheels and tires I bought locally on EBay. I don't recall the ride quality with the factory 16's, but the ride with the 18's is very harsh, moderate to high speed vibration and jarring over bumps. I got used to it, but i just put on the 16" d90's with snow tires I picked up and the ride is pleasantly smooth, well as smooth as snow tires can be. This makes me wonder if it's just the difference of having 18" with less rubber to cushion, or if possibly these wheels are bad, or a combination.

How does everyone else feel about their ride on 18" wheels/tires?

jcorenman

If it wasn't lifted, then it wouldn't need to be drawn down. That is a method described in the WSM, that IF the car has to be lifted and is sitting too high then it can be drawn down to the original ride-height for alignment. It is much better IMHO to align it as it is driven, without lifting.

If the ride-height has been lowered then bump-steer will be a small issue with bumps, i.e. the toe will change as the suspension compresses and rebounds over a bump. But driving down a flat road it won't matter, and driving down flat roads is what is scrubbing the inside edge.

I don't think the 18" wheels matter either, except for ride quality (less rubber = harsher ride). It shouldn't be an issue, but what is the ET offset in the front? (Width and offset are marked next to the valve stem on factory wheels).

So what the heck is going on??? It is clearly an alignment issue, and the only way that can be is if either the shop didn't do it right, or the alignment is changing after it leaves the shop.

Checking the toe yourself is not hard, do it like Mark K describes.

But all that is worthless if there is play somewhere in the system, and that is what I suspect is going on. If the tie-rods or rack is loose then toe-in will be all over the place.

So try this: on a relatively flat floor, center the steering wheel and then grab each tire and push it out at the front, in at the back-- i.e. try to make the tires toed-out. Check that the steering wheel is still centered-- don't push hard enough to move the steering wheel. Now check toe-in with your tape measure.

Now push each tire in the opposite direction-- toed-in at the front-- and check again. The measurement should be the same, within a few minutes of a degree. If not, then there is play somewhere-- a loose tie-rod, or excessive play in the steering rack (either internally or loose mounting bushings).

mark kibort

no, its not the tires either. sure, the 18s with lower profile tires will be a firmer ride, with more positive turn in because of less side wall flex, but its not going to effect wear. if it had vibration, they could have been balanced wrong.

what do you mean, "drawn down"?

if you are wearing the tires on the inside this bad, you have too much toe out, its that simple.

mk

mark kibort

As Jim says, the only real possiblity is that you have play in the system and it would have to be relatively bad. just jack up each corner and pull on the tire, top and bottom and then side to side. if you get a lot of movement, there could be the issue. the wheels could toe out during driving and press outward due to that play, but not at stand still. make sure the play is due to tie rod slop and wheel bearing, not steering rack bushings that would not effect alignment.

as Jim mentioned, bump steer, car being too low, is NOT even a minor factor, and even if it was, you need a real low car to have bump steer issues, which is more of a problem for race cars during straight line braking, and tire scrub during long constant radius turns. (i.e. turn 8 at willow, or 2 at Thunderhill) otherwise, the inside, drooping tire, just is toed in vs the loaded tire, and actually might even counter act each other, creating NO issue at all . (ie, the droop tire, toes in, the compressed tire toes out, and the net effect is no change. PLUS, it doesnt really matter due to the inside, drooping tire, not even really contacting the road surface, sometimes even lifting up in the air).
mk

[QUOTE=jcorenman;7131162]If the ride-height has been lowered then bump-steer will be a small issue with bumps, i.e. the toe will change as the suspension compresses and rebounds over a bump. But driving down a flat road it won't matter, and driving down flat roads is what is scrubbing the inside edge.

Checking the toe yourself is not hard, do it like Mark K describes.

But all that is worthless if there is play somewhere in the system, and that is what I suspect is going on. If the tie-rods or rack is loose then toe-in will be all over the place.

QUOTE]

Brett Jenkins

Hmm, that's a lot to take in.


The tie rods ends are new in the last year or so.
The steering rack is original, but now has solid Delrin bushings.
I considered checking, packing, replacing wheel bearings recently, but couldn't get the caps off and moved on to other projects.
One thing I've noticed is that this car pulls considerably when there's any undulation in the road. There is a stretch of interstate that perpetually under construction and one lane is a combination of the old shoulder and part of another lane, so it has some difference in it, ie not perfectly smooth. When I drive in this lane, the car will pull left or right. I thought it was due to the offset of the 18" wheels causing tramlining. I will drive this road with the 16" d90's on and see if it's improved.

IIRC, the front offset is 50

Mrmerlin

just get a measure of the front end ride height