dprantl

Jack up the front corner of the car and see if there is play in the wheel at 3-9 o'clock and 6-12 o-clock. Careful on the former because you want to discern play from the steering moving. Repeat on the other front corner. If there is no play, you are toed out on one side.

It really is very easy to check your toe in the front. Make sure the car is fully settled beforehand and is on flat level ground. Then get a long flat straight piece of wood, set it against the outside face of the wheel with the wood extending towards the front of the car as far as possible. The longer the piece, the more accurate your calculation will be. Mark a point at both ends of the wood. Repeat the same on the other wheel and make sure the wood is extending the same amount forwards/backwards. Mark the points. Now measure the distance between the rear points and the distance between the front points. The difference between these two values is your total toe. Ideally you want the difference to be as close to 0 as possible.

Dan
'91 928GT S/C 475hp/460lb.ft

mark kibort

It doesnt matter, its a NON issue. why do you keep bringing it up. you are just going to confuse the poor sole. If you think it is important with tire wear, explain why? Bump steer only means that the compression of the wheel into the wheel well will have different effect on toe changes depending on the ride hight. both sides would have the same changes and going over a "bump" on one side of the car, doesnt create tire wear. IN fact, as I have said, Ive been driving near 10,000miles on the same set of DOT race rubber, including practice during race days (I use my "A" set for qual and races) and there are NO wear patterns, AND Im at 110mm ride hight. the Lower A-arms are almost 45 degrees !

Its not that much to take in. sounds like the car is solid. you would have to have REAL bad wheel bearings to have an issue there. thats easy to check.
you have a bad alignment, get that fixed and check with the measuring tape as I mentioned using the level and a magic marker on the ground. (after driving the car for a long while) the fact that the alignment guy was doing something to "drawn" the car down, tells me he is lost. you are toe'd out, plain and simple. Now, as a side note, the car should not pull or tramline. I have crazy offset wheels and mine tracks straight as an arrow. if its pulling, you could have a full aligment issue. the rears might be off a little, vs the fronts. that would explain the front wear more on the one side.

mark kibort

I gave a simple way to do this. wood can have some bend in it, and could sway the measurements. just a common level placed at the front and rear of the tire, marking it on the ground. basically that will be about 19" apart, and then measure the front of the tire to the rears of the tires and see the diff. the fronts should be near 0 but ideally , 1/8" . I would imagine you have about 1/8 to 1/4" toe out as the tire wear tells me. but, the rears are off too, due to one side showing more wear.

one side, by the way, will not be toe out., compared to the rears, maybe, but generally, if the rears are straight, both fronts are toed in or out equally. the car naturally will center itself going forward, at the cost of sterring wheel position.

mk

jcorenman

OK, they're probably fine then.

Solid bushings is good, but the rack could be a problem. How many miles??

Wheel bearings are rarely an issue, but easily checked by jacking and checking for play with your hands at top and bottom as Dan and Mark described above.

I would push that down the list and worry about it later. It could be the 50mm offset, could be a worn rack, could be the lopsided worn tires (or all three).

I think the most likely suspect is radial play in the rack rod, i.e. side-to-side play at right angles to the normal in-out motion of the rack rod. You can check the effect on alignment as I described above, or jack the car and check for play as Dan described. Or just crawl under the car and grab the tie-rod near the rack and give it a firm wiggle in various directions. It shouldn't have any play, except in/out as the car steers.

If the rack rod is moving side-to-side because of worn internal bushings, then that translates into a toe-in problem-- and is also a major contributor to tramlining since the wheel is free to steer for itself over uneven pavement.

mark kibort

that kind of wear, is alignment, plain and simple. there could be an rack issue, and that is a real chance. good point Jim, but I dont think you can feel it by pulling on the tie rod. you need more force than that. I remember my loose tie rod. no tire wear, but on the car, I could only feel it by really pushing on the tire side to side. when the tie rod was off the car, it felt good!

check the alignment and I bet you are toe'ed out .25" in reality (front of the tire, to rear of the tire, comparing both front tires side to side measurements as described above)

GregBBRD

Mark:

Sorry, can't agree with this.

Your experiences are not everyone's experiences. Sometimes raw data...like actually measuring the amount of bump steer in a given amount of travel, is going to be worth more than one car and one driver's experience. The 928, in lowered form, is just plain awful in toe change.

mark kibort

Respectfully, what are you disagreeing with? I have measured the bump steer of our cars vs the amount of travel. We have a chart plotting it all out. yes, it is more as you get angles in the suspension components, but what does that have to do with tire wear? I've raced and driven on the street, or been responsible for , over (5) 928s all, with extremely low ride hights with no issues in tire wear, especially on the street, but if you look at the "data" why would there be any. There has to be a logical reason why I have had such good luck in the same car that everyone else has here. Ive been able to see the effects of toe out .25",and how it cleaned off the race rubber on the inside edge driving home from the track, after getting hit on the wheel in my race bending a tie rod. I can see how that went away, when i dialed it back to 1/8" toe'd in and didnt see any wear problems, street or track.

So, the tire toe's-out under compression of near 1-2"under braking, How long do you drive braking at that force? Generally, most drivers are not threshold braking on every stop. So, if not, then the changes to toe, under braking are minimal, and if one wheel hits a bump, that tire could be wearing for a mil sec. or so. Also, if you have a stiff suspension, that effect is less, because there is less dive, and you should be aligned with a slight toe-in anyway, to help here as well.

Lets talk about turn 8 at willow, or turn 2 at thunderhill. What is happening there? one tire at full droop, and the other at full compression. You have the data, tell me what the net difference of the two wheels is? If you look at the data, there are some trade offs on both sides, ironically, it might be better than if the car was at flat ride height to start. (because you might get more droop on on side than compression on the other.) regardless, the fact that under high compression that the lifting (drooping ) tire might not even be in contact with the surface, and the overdominant factor of camber change, might well over shadow the effects of "bump steer" issues.

On the street, its just not a factor. The data I have, and its probably more than anyone around on any car, is on DOT soft rubber, on the street, on a 928, lowered to the max, and not wearing the tire in any particular pattern. Its a tribute to the design that it can be aligned with moderate settings for the track, and still perform well on the street. Dont try that with your BMW at home folks. you will either cook your inside edge on the street , or have a car that handles aweful at the track, due to the amount of camber they need to perform well.

mk

GregBBRD

That's the beauty of this world, folks...anyone can be an "expert" and have an "opinion".

mark kibort

In this case, its neither. Not my opinion, and I'm no expert, but I can share 10,000 race laps of real world data that tires dont wear on the 928 when they are lowered. (Along with 200,000+ street miles combined). So, Im sharing what I have seen on our 928s
Show me a car that has this issue, and Ill show you a car with a crappy alignment, regardless of ride height. Not an opinon, fact. Now, if you want to have this same experience, just do what I did. Again, Im no expert in race set up, but I have found settings that are good for both. Remember Anderson ripping the heck out of his inside edges trying to keep up with the "911 jones" and their crazy camber settings a few years back? Well, what happened when he backed off his front camber from 3+ to 2 degrees. He was faster and had less tire wear.

The net net of "bump steer when racing, is that when the loaded wheel goes under compression, it toes out, but all that really does is desensitize steering, which isnt a bad thing. the other tire going into drop, often isnt even in contact with the ground , so it doesnt matter much. if you have too much bump steer under braking, the toe out will cause some wandering under braking, and thats when you know you have a problem. Either raise the car, increase spring rate, or toe-in the setting on car a little. all have effects and trade offs you need to consider. That's part of the fun!

Lets not get too off track here ( no pun in tended). This guys ride hight is probably near street settings. Mine, heck, my A-arms hit the chassis . he is tearing up his tires and its due to a bad alignment. Now, THAT is my opinion.

GregBBRD

I agree his problem is probably from a bad alignment....unless the car is "slammed".

I do not agree that bump steer is an insignificant issue....nor would Porsche. Have you seem to the extent that they have worked to reduce the amount of "directional changes" on the Cup Cars? They aren't doing this for the sheer fun of designing and building stuff. The less the tire chages direction, as it sweeps through the camber curve, the more stable and predictable the car will be. You simply can't have a tire "at the limit" and suddenly change its direction without upsetting the slip angle.

While this apparently doesn't seem to impair your driving style....and I respect that....I assure you that it does impair most other drivers.

dr bob

^^^^ Thank you, Greg. I got tired of beating that dead horse to death with MK.

To the OP--

Getting an alignment with new tires almost always means new tires installed THEN an alignment. They picked the car up to install the new tires, and stole the tire life from you in the process.

A car with a sagged front suspension will make the effects even worse, with results including the tramlining and bumpsteer issues you are experiencing. Since you are not racing the car and replacing tires every week or two, I recommend that you give MK's advice the respect it deserves as it applies to what you have and what you are doing. Spend a little time restoring the original ride height. Go drive the car 50+ miles, and take it to be aligned then WITHOUT RAISING THE CAR AT ALL DURING THE ALIGNMENT PROCESS. Alert the alignment guys that raising the car will cause you to go drive another 50+ miles before they get another shot at it, and you won't pay them if they raise it up. Simple as that. A reference to their revenue usually gets the right attention. Watch them and make sure they follow the instruction.

There is a great DIY alignmnet thread available with some searching here. There are some posts from MK that include his race experience, again his advice does not apply to your situation. There's also a decent video instruction from Andrew Olson that may help you. Even if you choose not to make adjustments yourself, you will be able to instantly identify a bad alignment before you trash another set of tires.

Mrmerlin

anyway what is the ride height Brett??

I had another customer come in with the worn inner tires.
I replaced the shocks and returned the front end to original ride height spec..... he had it set at 130 now its 170 ,
guess what no more worn inner tires after the 4 wheel alignment and new front tires
all other front end pieces are tight .
Best to check the front end RH with a stock size tire diameter

jcorenman

Something I learned many years (decades) ago was to never get an alignment from the same folks that you are buying tires from... It just never seems to work out quite right for some reason.

Having figured that out, I got our 928 (the 88s4 when it was 3-4 years old) aligned by an independent shop-- and THEY screwed it up, went through two sets of front tires in 6,000 miles. They were as ignorant as the owner, but we are all wiser now... right?

Also search for Earl Gillstrom ("captearlg" on RL), and read this:
http://members.rennlist.com/captearlg/928align.html

And print this for your shop:
http://members.rennlist.com/captearl...hydifshop.html

GregBBRD

Kibort's a great guy. He always seems very civil when he debates things....which is something you have to respect. You just have to realize, going in, that he will never conceed that he might be mistaken on an issue. He stands his ground....which is also something you have to respect. I suspect that he is gathering data from some obscure place to support his point, right now.

Brett Jenkins

I'll check the ride height and front toe when the weather improves a bit. Cold and wet right now.

I respect the advice and opinions given by everyone in this discussion. Like everything else, the useful bits have to be gleaned.