I have a 914 w/GT Flares and 911 suspension. I am having a set of custom 17" wheels made for it. I can not find the backspacing and offset dimensions for the front and rear wheels. Does anyone know what they are or where I can find them? Thanks in advance for your help

This seems to be the most difficult to answer question there is about 914s. I've found evidence that the original 5.5" 4-lug Fuchs have a backspacing of 120mm. For a 7" wheel to have 120mm backspacing, the offset would be 31mm. For an 8" wheel, the offset would be 18mm. That's all I've been able to come up with in concrete numbers, and it says nothing about how well the wheels fill out the flares.

There's also the matter of scrub radius to consider. I'm thinking about writing a thesis on GT flared 914 wheel offsets.

Thanks for your help Todd, I did find that the four lugs original Fuchs have a 120mm but I was not sure how to calculate up to the 9" rears. Does the 17" wheel change the calculation at all or is it simply the width of the wheel that matters? I would assume that the wheel size does not matter until you get the tire on the wheel.

Can I simply assume a smaller backspace (offset) and add spacers if I am too short?

I am also having trouble finding a custom wheel in a 9" rear. Has anyone ever put 10" on the back?

Your wheel width will be limited by your flairs, depending on how they were put on.

Backspacing and offset are two different dimensions. Backspacing is the measurement from the mounting face of the wheel to the edge of the rim.

The 7" 911R wheel is generally accepted as the widest wheel you should be able to fit on a 914 rear without modifications. That wheel has a 4 2/3" back spacing. There is a 944 8" wheel that is the largest you can put on the front of a flared 914 or 911, but I don't have that part number or backspacing.

I have a chart that I copied from an old Porsche Panorama that listed all factory Fuchs wheels with backspacing, but I don't have it handy. I'll add a post later with those dimensions.

Don't confuse backspace and offset. A smaller backspace will move the wheel out, so the smaller your backspace, the less likely you'll need spacers... and the more likely it will hit the fender. If you are having custom wheels made, you really don't want to be running spacers... that would kinda defeat the purpose of custom wheels.

A smaller offset moves the wheel towards the center of the hub, which will also move the wheel out, but it's a different measurement. Offset can even be negative.

Do you have the flares on the car? What width wheels do you want to run? I'd do a mockup to make sure you get what you want. Mount some wheels, measure clearances, and do some math. I'll be doing that when I get to that point, but it's a long ways away... I pretty much figure on 7" front and 8" rears, and I won't be having custom wheels made. I am considering a non-Porsche bolt pattern, though.

I am running Cup II 17inch rims: 7inch in front and 9inch in back. The front rims have an offset of 55mm which is matched up to a two inch spacer; the rear rims have an offset of 52mm which is matched to a one and half inch spacer. These are fitted inside the GT flared fenders and appears to put the center of the rim in relative alignment with the center of the bearings. I have good clearance on the outside flared fender lips and good inside clearance to the fender and suspension pieces.

Hope this helps you.

Hi, Perry.

Steve Hurt

Thanks again, I do not have the flares on yet but considering the weeks are an 8 week wait, I did not want to wait until I had the flares on to order the wheels, but I may need to do that. I want to run 17x7 on the front and 17x10 on the back, I am having a hard time finding anyone who makes a 9" wheel so I am trying to figure out of the 10"will fit. Take a look at my math and tell me if this is correct in looking at the offset on the front. What I have not been able to find is the backspacing for the rear flares.

120mm backspace( 4.72)inches- ((wheel width of 7 inches (229mm) /2))=+6mm offset for the front.

Again thanks again for everyones input

Thanks Steve,

The Cup II's are the Turbo Twist wheels right? It is odd that I have seen these wheels with different offsets, I assume because they were designed for different models. I thought I could figure it out if I had the offsets, but it looks like I need the corect backspace as well

The rims I am running ARE NOT turbo twist type. They are from earlier cars probably Boxer or equivalent 911 series.

Additional info is the difference between adapters and spacers. I am using adapters which do not require longer studs. The items which should be called spacers are the ones that need the longer studs. I called them spacers here in the thread and probably should have used the term "adapters". These adapters have snap fitting male and female machined lips and recesses which take the load of the rim. The lug and studs just hold the rim tight to the rim allowing the machined lips and recesses to their work of load bearing from the rim. The studs do not take direct load.

I will go back and check my documentation and see if I can put together a simple way that I looked at my rims, adapters, and tires. I think I may have some pictures at the different stages.

Steve Hurt

Thanks Steve,
I am somewhat at a loss trying to figure this out, I am going to take some measurements and see if my measurement get me back to the factory backspacing. I guess that is the only way to know for sure. Again any help would be appreciated.

James

If you haven't mounted any flares yet, you may be best off to wait untill you have the wheels mounted on the car so the body shop can use them to clearance the flares to fit. I have the factory GT flares on my car, and the 8" wide fuchs (15 "diameter) fit the rear GT flares nicely, so there is probably a bit of room to go wider, but not much. If you know what you need to fit over, a good body shop can make it work!

Your car may vary, but here's a graphic I made for a GT flare car.

Great info, Mark... is that front or rear?

That is kick ass, that's great!

My measurements are pretty close to yours. The biggest issue I have been fighting is that very few make the 8" or 9" wheel anymore if you want a more custom wheel. They start at 10". Based on my calculations, a 10" will be very tight.

See if this seems correct based on your diagram:
10" wheel=254mm
Usable space under the wheel well is 10.75"=273mm

273mm-254mm=19mm Basically 2cm clearance assuming you hit the offset perfectly. So I can not do 10" wheels unless I roll out the flares a little more.

Thanks guys, big help.

James

You need to factor in that alot of tires overhang the wheel.
Some overhang on a cantilevered sidewall by as much as 1 inch per side...so the choice of rubber has a pretty significant impact on your wheel width.

Its the rubber that rubs the fender and the inner fender, not the wheel.

Rich

Thanks Rich,

I see what you are saying, I not only need the figure the rim space but I also need to get the actual dimensions of the width of the tire application I will use. Sometimes you overlook the obvisous.