Drewster67

http://www.wheeldynamics.net/appguide.html

I just posted this in another thread. Hopefully it's not a repost.

chaadster

With regards to wheel diameter, I guess I am thinking more about wheel clearance than tire clearance, e.g. brake caliper rubbing. Aren't "Big Red" updates known to cause some issues with certain wheels?

Also, I don't understand your response to the "50-something" offset question. I thought you wanted to compile a list of possible wheel fitments? Anyway, the ET55, 7.5" fronts I mention are factory 993 wheels.

FlyingDog

Andrew, I saw that. Seems interesting, but I don't know if it's entirely true. I thought there were some that didn't work.

Chaad, sorry. I was saying that I may have false information. I thought 928 Specialists was correct about the 65 offsets for Cup IIs, but yours are 55. I would assume it's either a typo on 928gt.com or Porsche made 2 different sizes of Cup II fronts. I'll add yours as 993 wheels. The aftermarket Cup I/II fronts are 50-something offset (I should check because I have a set in plastic bags waiting to go on my car), I had assumed they had just gone with an easy to manufacture offset that fit most cars. Now that I know your offset, I guess they copied the 993 version of the wheel.

There are some wheels that don't clear brake calipers, but I think they're all smaller older wheels (ie: some 944 Club Sports will not work on 928s). If people post the ones that don't fit, I'll make a note of them.

chaadster

No problem. I'm also not impuning 928 Specs info; they're probably correct that the only factory Cup wheel fitments for the 928s were ET65 (for the GTS).

RacerDave

Needed information:
Wheel width 18x 8.5 ET52 front, 18x 10 ET58 rear
Wheel offset
Front/Rear
Tire width 225/40-18 front, 275/35-18 rear
Fit? Fills wheel wells, no rubs so far, about 100 miles of spirited driving.
Rub? Which side, in or out?
Spacer? How big? No spacers
Rolled wheel well lips? No roll
GTS?

1982 928S

This helped me make my decision, so hopefully it can help someone else out.

Art_Z

19x11 et 67 295/30
19x8 et 57 235/35

1" spacer on the rear

rear fenders rolled, and then rolled some more. rubs on bumps in the rear, need stiffer shocks.
front works great, no rubbing

mark kibort

275s up front and 305 or 335s in the rear on 9.5s and 11s
backspacing , 8" front and rear!
fenders rolled, and on the Holbert car, i did bang it out a bit and repaint(no flaring) and so i could use the GT spacers (17mm) Scots car has the same set up, and no special work to the fenders except some rolling.

this pic is the 335 on the rear of the holbert car. the 305s have a little more room, but no rubbing for either at any time!

mk

sublimate

Front: 18x8.5 ET52
Rear: 18x10 ET52

Front tires rub a bit w/ 235s. Going to try 225s or 215s when I reshoe in a few weeks.

FRporscheman

What's the offset on '84 manhole wheels (928S)? We're about to start spiffing up my dad's car and thought it might be fun to borrow my spare 968 wheels now and then.

piccardo

For tire wheel combinations of 25”diameter

OFFSET MAX TIRE WIDTH

FRONT +65 to +68 mm 265 mm or 10.43
REAR +52 to +60 mm 285 mm or 11.22
________________________________________________________________________

For the S4 the wheel tire combo is
STOCK FRONT 16”x7” with 225/50-16 this equals 8.86 wide x 24.86 diameter

STOCK REAR 18”x8” with 245/45-16 this equals 9.65 wide x 24.68 diameter

The STOCK wheel tire combo is a minimum or a stating point.
Front Min +65 offset/ 8.86 wide/ 24.86 diameter.
Front Max +68 offset/ 10.43 wide/ 25 diameter.

Rear Min +52 offset/ 9.65 wide/ 24.68 diameter.
Rear Max +60 offset/ 11.25wide/ 25 diameter

So if I understand this correctly, then as long as your wheel tire combo is 25” in diameter these ranges should work. There is a little spreadsheet available from Discount Tire. If you input your tire ( 245/35-18) it will tell you the over all diameter and overall width. So the only thing missing is how do we know what tire sizes fit what wheels.

AO

I've been slowly working on an excel-based wheel/tire fittment calculator. I think it's pretty close.

My main issue is know the max values for rubbing on the inside for both front and rear - and of course to complicate things, it depends on the wheel diameter. If anyone has this info, I'll be happy to incorporate it.

Click here to download... Wheel fittment calculator.xls

January 24, 2008 update: I've just updated the calculator with some additional wheel info (Thanks to Randy V!). -AO

Andre Hedrick

D90's front 7x16x55mm w/ 3mm plates to make 52mm offset to tuck correctly as on can, and D90's rear 8x16x52.3mm clean. '81 w/ BigBlacks epoxy painted red.
Also note S4 brakes with '81 backing plates need heavy modification! Several cuts and one 2 inch hole in each.

FlyingDog

Nice work! I've been meaning to do that, but never quite got around to it.

AO

Thanks... I basically followed your sheet. Just made it pretty and added some usability functions.

svp928

Front, 17 x 10, 65 mm offset. Rolled lip. 255-40-17 tire.car is lowered, front tire is 3/4 inch up into the fender. Wider tire would fit with less offset, but then inner edge of wheel hits lower control arm at full lock.

Rear- 17 x 11, 60.3 mm offset. Rolled lip, hammered inner fenderwell. 285-40 tires, edge of rim is level with top edge of fender. Can't get finger between tire and rolled lip, rubs slightly on inner fender.

HRE 3-piece wheels.