drnick

yeah, it is better to do the alinement with fresh rubber and if the tyres are worn on the inside edges then they are not too good. if you dont want to buy new rubber for the front at the minute, then id wait untill you do before getting the alinement - its worth it to know you wont be wearing out the next set of rubber prematurely.

JPTL

+2 on that. The adjustments are in degrees that can equate to a tenth of an inch. If any tire(s) is unevenly worn like you describe, your camber will be off when you put the new rubber on.
You need new tires anyway, might as well get them on now & have the alignment done with good tires. Find a couple of speed bumps or a jiggly road and tool around for a few miles so that your car's fully setttled before your alignment.
The rolling procedure gets the lasers calibrated and locked in by getting a read on the reflectors that are mounted to each caliper/clamp. It's pretty neat how this system works, because once the machine is 'locked in' the car can be rolled and adjustments can be made to the alignment - the whole time the machine gives a real-time readout of the specs. Like Bob says, the 'software' is simply a diagram or road map that helps the tech who hasn't done a 928 alignment before. It will save considerable fiddling around for the tech who has never done a 928 - regardless of how experienced he is.
It there's anything that you want to supervise, it's the tech getting the calipers on the rims of your wheels. Depending on the rims and your tires, it may be a little tricky. If the tech is ham-fisted and/or impatient, he may gouge up the rims or give up altogether. Just know that it can be done, and it can be done without gouging your rims. It takes patience in some cases.

JPTL

Jim, when you mention how much wear you have on your front tires you've got me wondering what is off so much. If your car was lowered at some point without a follow-up alignment, that could lead to some tire-eating results (big changes in camber and/or toe).
If you aren't entirely happy with your ride height, or think that it may be uneven, before the alignment is the time to fix that.

Jim bailey - 928 International

The typical alignment done by lifting the car ALWAYS screws up the toe and ALWAYS wears the insides of the tires......ALWAYS. MOST 928s that we take apart have such tire wear beacuse nearly every alignment guy lifts up the car as they make adjustments and the car does not settle so the toe is WRONG after a few miles of driving and it eats the inside edges. Take it back to the same guy and he LIFTS it up again and checks the toe and it is just as he set it before. Drive a few miles and the toe is wrong and it eats the inside edges....You almost have to hold a gun to their head or they LIFT the car. I know of no other car which has such an issue with being lifted. So you MUST be sure that the guy doing the alignment rolls the car back and forth after adjustments and does not just move the lever on the lift !

Emickelsen

I would be very interested to see that.

JPTL

I forget who it was, but somebody did just that. Hung around and posted pictures of the procedure. He posted them in a new thread - or added them to an existing thread.
Jim, here's what to expect print-out wise (first post of Rob Edwards' thread)

greg928GTS

Here's the thread with pictures of the last alignment I had done.

Greg

https://rennlist.com/forums/928-forum/378409-sub-100-alignment-my-experience.html

G Man

Thanks for the pics of the alignment. The shop I went to uses some sort of reflective panels they attach to the wheel rather than the cameras. Is this the norm?

Tom in Austin

Help me on this one ... JPTL says "If any tire(s) is unevenly worn like you describe, your camber will be off when you put the new rubber on."

What difference would the condition of the tires make when the alignment is being performed? Aren't the alignment measurements taken using equipment fastened to the wheel? Theoretically, you could align the wheel without a tire, so I don't see how the condition of the tire matters.

I ask because I have a slightly-worn passenger tire and was not planning to replace before getting my front-end straigthened out. Just seems intuitively that the camber must be based on the relative position of the wheel (or the rim surface to be exact) irrespective of anything going on with a tire ...

dr bob

The two front tires need to be the same height, two rear tires need to be the same height, so the car is not leaning during the camber measurement. Camber is measured compared to the local gravity not the rest of the car, so a car that's leaninig at all will have similar errors in camber setting.

The Big Deal for uneven tire wear is that a good alignmnet tech will "trim" some settings, like caster, to get the car to go straight down the road. This is how one compensates for accident damage or frame misalignment. Worn bushings will take some tweaking too sometimes. Anyway, you really don't want to align and tweak the settings to counter the effects of uneven tire wear. If you really need to get the alignmnet done with uneven or heavily-worn tires, just have the settings done per spec, and suffer through any uneven results until you get the tires replaced. Some places may refuse to do this or ask you to waive the "satisfaction guaranteed" part of their agreement. Or borrow a set of known-good wheels/tires to use during alignment. Be sure to drive the car enough to settle the suspension after swapping wheels, of course.

SharkSkin

Bob's right. What happens is that the load on the suspension is different with an unevenly worn tire. The difference is small but measurable.

JPTL

Yep. I figured that I'd let the only guy with the Alignment Avatar field that question.

dr bob

You guys have way too much faith in a blind guy who checks alignmnent with a tape measure... I guess a new avatar is in order.

Folks having an alignmnet done, even with new tires, should verify that the new tires really do have the same pressures side to side on each axle. It's a good idea to have them close to your target pressures, but the fact is that they need to be exactly the same side-to-side. Same deal with ride height-- Factory limits is 10mm deviation side-to-side, and even that's extreme. 10mm difference at the suspension pads translates to more than half of the camber a stock 928 should have if the car is actually leaning.

Jim bailey - 928 International

Some alignment guys even suggest that if you are a bit LARGE and mostly drive alone that the alignment be done with your weight in the car....corner balancing as well not that I know anything about that ...

dr bob

There's a real good case for that. IIRC, the wsm even mentions how much gas, and recommends driver's weight in the seat for precis alignmnent. Me, I've been sandbagging on this little detail.