mark kibort

well, there you go.

AO

My best guess is based on my GT of 103mm. Since your fender lip is not rolled (GT is from the factory) I'd say about 100mm.


The '87 doesn't have a full inner fender liner like the '91 GT's, but it should be around 200mm.

So that means you have about 300mm to fit a tire in. This is why a 295 tire just fits.

Now take the 295 and devide it by 2. This gives you 147.5. This is where the offset comes into play. If you have a 51mm offset wheel, add the 51 to 147.5 and this is how far the tire will stick "in" from the surface of the hub - 198.5mm in this case which is less than 200 so your tire would fit. Now subtract the 51mm from 147.5 to get 96.5. This is how far the tire will stick out from the hub. Since 96.5 is less than 100mm it should clear.

Again, when you get to a 295, you're really getting close to the limits of what will fit without modifications. Mine rubbed on the inboard side just a bit, so I added a 3mm spacer. This shifts everything outward. So going back to the example, 96.5 would then become 99.5. In this case, 0.5mm is not enough clearance to not rub. I think you need at least 2-3 mm.

Make sense?

Franks928s

I think we have a "BINGO!" - well Maybe. Would these same depths hold true for the fronts as well? Is there a rule of thumb for measuring the demark for when the wheel would start to rub upon hard turning?
Am I safe to presume that the goal is always to get the rear tire offset as high as possible (naturally, without rubbing the inner fender/stuff) assuming one is trying to fit the widest tire possible?

Frank

AO

The off set is how far from center you are. On the fronts, I think you want to have an offset of at least 55mm for an 8" rim.

For the rears, personally, I don't like a big gap between the fender and the tire, so I would look for a smaller offset.

Franks928s

Do you have any rubbing issues on your fronts when turning hard? I'm thinking about going with an 8.5" wheel and about a 9" tire width. Offset either a 56 or a 59. Is there a manner in which to determine if they will rub when turning?

Frank

AO

No.

You'll hear it. Also there is the potential for the fender to cut into the tire. 9" tire is a 225. If you;re going to run a 8.5~9" wheel, you should be looking at a 235 or 245 minimum.

F451

Also keep in mind you may not have rubbing when turning, but you may run into rubbing issues when driving over bumps (on the front and rear).

So, simply putting the wheels on, letting the suspension settle, and checking steering lock to lock, may not tell the whole story.

And I think its already been mentioned, but different tire brands/models of the same size can in reality have slightly different dimensions, so something to consider.

Franks928s

235x40x19 is the tire I was thinking of with an et56. I kind of thunk I would hear it if it rubbed but would I'd really like to avoid the expense of fubarring the wrong tires/wheels on my front With your earlier calculation, the 235's with that offset would give me approx 1.5" of play to the fender edge. Wouldn't my tire width be the same with either 8" or 8.5" wheels since the tire width would be a 235 on both?

Frank

Franks928s

HI Ed, I'm hoping that adding bilsteins, new springss and the 928 spec sway bars will, as a by product, help ensure that I won't rub from bumps. Point well noted regarding the tires. I'm certainly looking at their specs. I'm partial to the Bridgestone RE050A Poles. I'm most concerned about the front tires rubbing when turning.

Frank

AO

Forgot to mention, that was for the rear's. You can figure out the fronts through my Wheel Fittment Calculator

Franks928s

I used Andrew's calculator and verified that my selections are a good fit. I've attached the download link to the calculator so this thread might be all inclusive for others in the future who are seeking to learn the intricasies of 928 wheel fitment be it 19" or others.

https://docs.google.com/leaf?id=0BzC...thkey=CK3SrvkH

Frank

Franks928s

SO....Here's what I concluded:I remain uncertain if I will go with 18" or 19" wheels. Although I'm looking to add size, I am not interested in going extreme but rather larger and what I consider to be "scaled" to my likes.

My two wheel/tire choices are the following.

18" RH/Speedline P3.6 with silver fronts, polished lips and gold/red crested center caps

Front: 8.5x18 et 59
235x40x18 Bridgestone RE050A Poles

Rear: 11x18 et 52
285x35x18 Bridgstone RE050A Poles


If I go the 19" route, the choice will be:
19" 997 Turbo wheels with the titanium painted spoke sides and polished front/lip with silver/black crested center caps..

Front: 8.5x19 et 56
235x35x19 Bridgestone RE050A Poles

Rear: 11x19 et 51
285x30x19 Bridgestone RE0f0A Poles

The color of the car these will go on is soon to be newly painted "Gasurit-Granite Green Metalic"

The sizes of the tires have also been influenced by:
1. maintaining a front offset of a minimum of et55 to avoid any steering conflicts (see Chadwick post)
2. mainitaing a one step in scale between front and rears; i.e, 40's and 35's
3. Designing a combination that I can find sizes of Bridgestone RE050A Pole tires since they are my tire of choice.

Here are pictures of the two wheels. If the 997 Turbo deal goes thru, those will be my choice, otherwise, I will invest in the RH wheels and be as happy as one can be . Pictures of the two finalists are listed below.

Thanks to all of you who helped educate me along this journey!!

Frank

Chuck Z

Turbo 19s = thumbs down (just not a good lookin wheel IMHO - especially on a 928)
RH 3.6 = thumbs up (got a set paint midnight blue metallic)

Tom. M

I've been trying to get Andrews calculator..but it says page not found..

anyone have a copy they can shoot my way??

thanks

AO

Tom... Shoot me your email and I'll send it directly.

Maybe I need to host it somewhere else...