AO

I can't seem to get this wheel offset thing down. And I suspect that I'll probably be buying a set of wheels in the next 6-12 months, but the offset issue scares em as I don't want to buy a set and find out that the don't work.

Does anyone have a thread or link bookmarked for wheel offset on the 928?

If there isn't one, as all 928's are not created equal, I've been thinking of making up a chart/matrix that shows the front & rear min/max wheel offsets (without rolling) by MY of 928. Of corse, rolling opens the field up. So anyone willing to help?

Art_Z

this is the one thing that scares me about the wheel thing too. The whole concept confuses the hell out of me , and even though I'm Polish, I wouldn't consider myself dumb!

MarkRobinson

Yes! 928 & S, S4/GT, GTS, 928S with '78-81 spindles & S4 brakes, etc.

With/without rolling fenders....please chime in.. Unfort., in the past, I just ordered wheels & didn't make note of the offests.

Mark

hinchcliffe

Of course the '86's have the long studs and spacers, right. An then there is the bolt on spacers with the GT and then all the wheel widths...........

AO

I envision I handy dandy reference chart that will give you a range of wheel sizes.

I thought someone had posted how the wheel offsets are calculated. If I had that plus the wheel to well/suspension arm dimensions, I think I could have Excel populate a chart in a matter of minutes. Anyone have this info?

AO

That's exactly my point... There seem to be so many variables, that I wish we could just look it up in a nice big table. Model Year across teh top and wheel size (front & Rear) down the left. Then inside each square, there would be a min/max offset. Pretty simple really. Just need to know the variables.

hinchcliffe

Take the overall wheel width minus the backspacing (rear of wheel to hub face) and convert to millimeters and there is your offset. Now there can be both negative and positive.

Its the offset from the centerline of the rim width.

My 17" x 10" rears needed a 15mm spacer to fit well. They are 67mm (2.63in) offset with 255/40 tires. They would probably fit without the spacer but would be touching the shock inside. I plan on larger tires soon enough 275-285. With the spacer and 255 there is clearance on the fender side and more clearance on the shock side. When I go to bigger tires I may need to roll the fenders out.

Kind-of make sense?

drnick

mark kibbort has posted useful info on this in the past also check DRs website under pics and look at what the GTS there is wearing on the fronts, i think offsets are mentioned. the issue should be confined to what physicaly fits without fouling anything rather than what is 'correct' for the 928.

AO

Ok, so a 9" wheel with 0 offset would stick in/out 4.5" (114.3mm) from the face of the hub. Right? I assume positive offset bring the wheel in closer to the center of the car, right? So in my example above, if the wheel had a 50MM offset, the wheel would stick out 64.3mm (~2.5") and would stick in 164.3mm (or ~6.5"). Simple enough.

Now the question that I really need to know is at which point inboard/outboard will the wheel rub?

AO

Exactly! No rolling. Just what fits - Porsche or otherwise.

AO

Here's a nice image courtesy of Fikse.

Tony

What wheels are you looking at Andrew?

IMHO and from my experience the TT Twist are
They have an OEM look, they update the car tremendously and you can get 295s on the rear of an S4 with a slight tug on the fender and a role of the lip.
Since you have a GT, they may just bolt right up?
You will need wider wheels, no doubt about that.

FlyingDog

I started one. After reading through about 5 wheel size threads, I gave up. The tire size issue is the killer.

Somebody who can prgram needs to make a Miata tire calculator like tool. Instead of just calculating diameter it would calculate distance from the hub inward and outward then compare that to measured wheel well sizes. It wouldn't be a guarantee of fitting, but it would be fairly close.

AO

Actually I'm kind of partial to the Carrera III 5 spoke 18". Never cared much for the twists - mostly because of the right left issue. But I really would like to try and develop this chart. It sure would be a handy refence for everyone.

FlyingDog

You also need to know tire width at the tread, tire width at the widest point, tire diameter...