A few days ago I read a wonderful dissertation by Kim (something) that detailed the unique 928 wheel off-set requirements as well as the wheel/tire possibilities, even for custom made wheels. Of course I propmtly lost the URL or forum page that is was at. Anyone else read it? and know where it is?

 

Probably Kim Crumb?

 

Be good thing to add to the 928 Forum on a future issue. Or get posted here so that it is researchable. It was one of my first questions as a new owner and I see the same questions posted here repeatedly.

 

Hi guys, I can advise you that the wheel offsets that are required are 60 to 65mm at the front with 8 inch wheels, remember that the GT came out with 60mm offset wheels but I believe Porsche rolled the edges.

I fitted 8 inch wheels with an effective offset of 65mm and there has been no rubbing at all.

On the rear I used a 10 inch wheel and the offset required is 61 when you use a 285 tire. remember the offset requirment changes with the width of the tire. The offset from the factory with the 9inch rim was 55mm and that was with a 255mm tire if my memory is any good. I have not had any rubbing at all with the above offsets. Hope that helps. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

 

I believe this is what you're looking for:

<a href="http://home.wxs.nl/~Jennit/Technical/Tips/2/MyTip274.htm" target="_blank">http://home.wxs.nl/~Jennit/Technical/Tips/2/MyTip274.htm</a>

REC
85 928s/garnet/saddle tan

 

Good find REC. I wonder who's website that is with excerpts from the Rennlist Listserve - anyone know?

I'm going to post the text here so that it will be available in the archive in the event that site goes away:

===========

There were the Carrera Cup Wheels, from the back of the 911/964. They are
9.5 x 17, 68 offset. Just the specs I wrote about way back in '91 in my
PROJECT 928 series. Use 'em on the front as is, and with the GT spacers
on the back. A little heavy for my tastes, about 27 pounds...as I later
pointed out in my wheel and tire story, about five years ago. If you
gotta have that specifc look, it's the best answer. Oh, these were one of
the wheel sets recommended in for the 928 GT CUP in Germany, and was part
of the published specs. It was nice to have them confirm my specs a few
years later! I've faxed all this stuff to DEVEK, and Marc is going to
publish all this data on their website, coming soon...under the heading
"Alignment Rack." That way everybody can see where we were in the early
to mid-90's, and that the factory's own work on the 928 for track
use...which was all done separately, of course...is congruent. Hope this
data helps! Kim

============

John:

The return of the great Wheel Question. Let's get the facts out
(again.) Every 928 ever made came with a 65 mm offset front wheel, and
were 7's or 7.5's (of various diameters.) The exception? A few '89 928
GT's which had a 60 mm offset front wheel, which is also the only 8" wide
wheel. (That's the Club Sport 16" forged wheel, the last of the forged
wheels from Porsche for the 928, and it still only used only a 225 tire.)
The rear wheels range from 7's to 9's, with offsets ranging from 65 to 55
mm. Tires from 225 to 255. (Sometimes with a spacer.) So the rear is
always easier to fit, the front is always the difficult fitment. So? I
always check for the front wheel first! Who cares how many rears you can
find (that don't have a matching front that will fit properly?)
As I wrote in my wheel and tire story in PANORAMA back in December '97, as
soon as you apply that 60 mm or more offset criteria, there are very few
wheels to pick from. All the other Porsche models use a strut suspension
upfront, (unlike our more advanced double "A-Arm suspension) so they go
"out," not "in" like we do, when looking for wider wheels. This "thread"
actually goes back to the PROJECT 928 car (in PANORAMA in the summer of
'91) when I made 9.5 wide front wheels that fit (68 mm offset) when all
the 56 mm offset 8.5's didn't work! (Tire rubbing on fender.) The
factory later confirmed this with those exact rim and offset when doing
the 928 GT Cup stuff for the German Porsche Club. (They used the 9.5 x17,
68 mm offset cast REAR wheel from the special Carrera Cup racecar...very
heavy and not inexpensive, confirms the specs, but not a great "answer.")
The technical data has been published by me a couple times, and apparently
is treated as an "inconvenience," in that it eliminates the vast majority
of inexpensive Porsche 130 mm bolt-circle wheels, there seems to be a lot
of resistance. When I took copies of the Factory 928 GT wheel specs to
the big SEMA aftermarket trade show, (in '95) to give out to various wheel
companies N/C...in hopes of encouraging better 928 fitments...I was
practically thrown out of a lot of booths...many obviously didn't even
want to "know." "Caveat-empor!" And any pretty "side" pictures on a
website don't prove that it really fits properly! I usually get a phone
call like this: I just got a good deal on some 993 (or you fill in the
blank on some jazzy late style wheels) what kind of spacers do I need Kim?
My answer? How good are you at spacing IN? Cause that's what you'll
need to do with that 52, 55 or something like that offset front wheel.
Usually there's a big silence after that. Save yourself from the same
mistake! Mostly what it boils down to is that the only way to get big
tires on a 928 is aftermarket multi-piece wheels. Yes, they are more
expensive than all those cast 944/911/Boxter wheels. AND you can get them
custom, so they actually fit! Like? 265's (F) and 285's (R) eighteens on
a 928S4/GT. Without rubbing the fender lips. A nice set-up for a late
model 928 S4 or GT. Those are real Porsche sizes (from the back for the
C2 Turbo and C4 Turbo respectively.) go through a zillion questions with
various 928 owners, apparently still hoping to find an exception, those
one set of inexpensive one-piece wheels that's going fit. They spend
hours, and days on it. You can search all want...they're all wheels for
the other Porsche models, being presented as "for a 928." NOT! As such,
since you know their front offsets don't match those of a 928 stock, they
really don't fit a 928, least of all when we're trying to maximize the fit
in the wheelwell! As far as putting bigger wheels and tires on a 928
(like the set-up I mention above) it isn't going to happen that way! Save
yourself the wasted effort. Forgeline, OZ, HRE, Kinesis, RD Sport...they
can all build what you really want! Get forged centers, while you're at
it! Having fender-rubbing set-ups, while you can get your fist between
the wheel and the coil spring on the huge clearance on the inside... now
that makes absolutlely no sense to me! 65-68 mm fronts and 52-60mm offset
backs...that's what works, unless you have flared fenders! (Which makes
the rear of the GTS the one exception.) DAAAAA, using the factory offsets
works, moving it out a lot doesn't. Sorry, I can't change the laws of
physics or economics! Kim

 

It's Theo's page - just remove the text in the above link past Jennit/ and you'll get to the main page.

Good resource page, and even searchable.

REC
85 928s Garnet/saddle tan