mc05duck

I think the link is broken, I couldn't connect.

Kris H

https://rennlist.com/forums/924-931-...el-thread.html

fixed.

LuigiVampa

I must have a mental block with all this as I can't figure out how to pick out wheels for my 1987 944 turbo.

I track the car and want to go up to 18 inches - perhaps 8 inch wide in the front and 10 inch wide in the back.

Front and rear backspace are both 153.9mm/6.06" and offset is 52.3mm/2.09"

I watched some youtube videos on backspace and offset and am still confused. Do I have to care about both measurements?

If I want this wheel on the front:

Offset: 50mm
Backspacing: 6.50"
Bolt Pattern: 5-130

And this one on the rear:

Offset: 43mm
Backspacing: 6.69"
Bolt Pattern: 5-130

Will they fit and do I need a spacer? Do I need a 2mm space on the front and a 9 or 10mm space on the rear?

Many thanks.

rlm328

The rims on our cars are diameter and width by ET not backspace. ET is how far off the center line the inside of the hub is. You can convert pretty easily.

ET = (wheel width/2) - backspacing

LuigiVampa

OK - I have brain lock on this issue for some reason. Thanks for the formula to figure out offset, but if you have the offset figures how do you calculate the spacer?

If the offset (front and rear) of my 951 is 52.3mm and I want to put a 50mm wheel in the front and a 65mm wheel in the rear can I do it? Will the wheel in the rear stick out too much? The wheels I am contemplating at 18in.

Many thanks - I am sure I will understand forever more once I get it through my head.

catamount

There is something else to be aware of besides the standard specs. Some wheels, including Porsche wheels, the fitment over the hubcap can be problematic. I have a set of 18" Porsche Sport Classic II wheels from a 996 on my '87 951. The front wheels don't quite fit over/around the hubcap. So, the possible solutions are, a) spacers on the front, b) mill the wheel, c) make a new hubcap solution, d) run no hubcap. I solved it by using a 5mm spacer. This was the easiest, cheapest solution that allowed the hub to continue to be protected with a cap.

lart951

how wide is the wheel? if the offset is 65 and the wheel is 11" wide you'll be fine
the 65 offset means that the mating surface of the wheel to the hub is shorter not longer, the wheel will go deeper into the tire dwell

LuigiVampa

Thanks Lart and Cantamount. Despite reading up on this late until the night the 65mm is deeper has put some of the gears in my brain into motion to better understand this.

Heading to Watkins Glen in a few weeks and want to get my little 16s off and put on some big boy 18s. Tire Rack has so far been useless in recommended anything other than a set of BBS wheels at about $900 a wheel! At that price it would rival the cost of my whole damn car!

rlm328

I have an App on my IPad that I use and really like for doing all of the calcualtion in regards to fit. It is called "Rim Offset". It takes into consideration the suspension, brake caliper, inner and outer fenders in relationship to your rims. It is handy for making an informed decision in your rim purchase.

Instead of speaking with tire rack I would contact the wheel manufacturer and ask them about fitment. If BBS cannot answer your question then go to some who will. I have extremely good luck with CCW.

Catamount is correct in that our wheels are "Hub Centric". This means the hub ceters your wheels and not the lug nuts. SO this needs to be specified but ususally when you give them the 5 x 130 bolt pattern they already know.

mc05duck

I went with a powder coating solution to my Wheels kunundrum....

catamount

Just to clarify my comments about my 18" wheels, they are hub centric. The fronts are 7.5"x18" and the rears are 10"x18". The rears fit perfectly with the hubcap in place. The fronts fit perfectly if the hubcap isn't installed. It appears that either there isn't enough depth in the wheel for the center/top of the hubcap or there isn't enough depth for the edge of the cap. Anyway, it's an interesting twist. I've wondered if the 8"x18" fronts would have the same problem.

LuigiVampa

Thanks RLM and catamount.

Baptizo

17"x9" and 17"x10" forged CCW's with UHP Summer tires (force load balanced) are currently on my '86 951....love 'em. The car is otherwise bone stock and original. Peruse the for sale ads here on RL and you might find something you like with the right offset for an '86 and in your budget - that is how I found the CCW's.

jmj951

FYI, the cap can be ground down to accommodate. I took a grinder (and then a file) to the lip on that cap and that was all it took.