928fan4life

on the 92-95 gts they use the 35mm spacers and on the 88-89gt they use the 17mm spacers. Which type should I use for my year??

mark kibort

depends on the rims you have. ive used the 17mm spacers with flaring the fenders while using 11" rims. however, without the spacers, an 11" rim works well. now, with a 9" rim, assuming the same backspacing, certainly, the big GTS spacers will work and put the rim closer to the edge of the fender.

all the chassis are about the same in the rear. however, i did have a stock spacer on my 84 about 17mm that worked well. ive also mounted all my same race wheels on a 79 too.

so, again, it depends on which wheels you have.

mk

928fan4life

I have the 9 in x 17 in rear wheels from a 1995 993 carrera. They have a 55mm offset. Would the 17 mm spacer work or the 35mm? Is the 35mm too much?

mark kibort

Now, on the rears, to the edge of the fender, using a 11" rim, you need 63.5mm offset., at 10" this becomes 50.8mm and if you have a 9", it would be 38.1mm. since the rims you have are 55mm, you need to move them out 17mm (getting that 38mm offset) and thats exactly what the spacer will do, so its right on the money. Basically, you will have the tire as close to the fender now , with the 17mm spacer and the 55mm offset 17x9 rim, as i do with an 11" rim, no spacer and a 305 tire with 62mm offset/8" backspacing


mk

928fan4life

Thanks so much for the help! So if I go out and get a set of 35 mm spacers that should work nicely correct??

Also, I have the 7x17 front rims with a 55mm offset. Would a 225 tire work ok up front or should I get a 215 tire for up front??

mark kibort

no, it sounds like you need the 17mm spacer. 35mm will be too much based on my calculations. up front, 55mm is actually 5mm too far out. now,on my calculations on front, 5mm is no problem. definitely do the 225s and not the 215s. 215s is a joke of a tire on a 3500lb car!!! you should be fine. actually, i use 5mm spacers up front on my rims so thats just wher you will be with your 55mm 17x7" rims.

mk

928fan4life

Thanks so much for your help mark. I will post pics once I get the rims in and get them mounted on the car.

928fan4life

Do you know of anyone who has a set of used or new 17mm spacers???

928fan4life

Another question, I found a set of 21 mm spacers. Would these work on the rear wheels with the 9 inch tire and 55mm offset?? Also, do I need longer bolts so I can screw in the nuts for the wheels??? Thanks

mark kibort

rear rims need 50mm offset if we are talking about a 10" rim, now, with a 9" rim, you would need 38mm offset. so, if you want to put those 9" rims in the rear, you would need 17mm of a spacer to push it out to equal the the 38mm offset of the correct rim , but using the 55mm offset rim. any more, and you could have rubbing issues, however, 4mm should be close, but maybe ok with 255 type tires. yes, you need longer studs or you need bolt on spacers. I use bolt on spacers in the rear, and i changed the studs in front to accept slip on spacers.

mk

928fan4life

how hard is it to change the studs?? What length of stud do I need??

mark kibort

the rears are really hard, and probably not worth it as you can get a bolt on spacer. the fronts are pretty easy. lenght depends on how wide you go in front
mk

928fan4life

I am new to this.. how does the bolt on spacer work?? Where does it get bolted onto???

Garth S

Good advice from Mark to use bolt-on spacers if required: a bolt-on spacer is a self centering (hub-centric) disc of X mm thickness with 5 wheel studs embedded in it. on the same 130mm bolt circle, there are 5 more holes that allow it to be bolted ( with special nuts) to your car - them the wheel is added, spaced outwards by X mm.
I have bolt-on spacers on both cars, now fitted with 16" wheels - and have just purchased 993 wheels with the identical widths & offsets as yours: I'll likely have to recalculate how much spacer, if any can be used for our new rears. The fronts at 7XI17 ET55 are a straight bolt on. I think the rears are also a straight bolt on, but can be spaced slightly further out to fill the wheelwell. So let's try out some #'s .....
Here's one (convoluted) way to calculate what size spacer may be required: With a 245/45R16 on a S4 rear wheel 8" wide, ET53 - a max spacer without rolling fenders, etc. and at stock ride height - is 21mm: at least on my car! The 993 wheel you have is 25mm wider, and a 255/40R17 is 8mm wider on these respective rim widths than a 245/45 on an 8": split the total of 33mm in half = 16.5mm ( half 'hangs out' each side, keeping the centerline as reference); therefore, with the 55mm negative offset, correct the outer rim to fender by -2mm, and add +2mm to the inner side, compared to the ET53 of the S4 wheel. This will leave a 17x9 ET55 14.5mm closer to the fender than a stock S4 set up - and 18.5mm closer to the coil spring.
I think that would be fine without a spacer - but haven't verified on the inner side, although I would not foresee a problem. There will be no problem on the fender side.
Now, if you wish to 'fill' the wheel wells to the max., we know a spacer of 21mm works on the S4 wheel; therefore, if the 14.5mm calculated above is subtracted from the 21mm, we are left with ~6mm =~ 1/4".
If the simplistic math is not screwed up, you can add a 1/4" spacer if desired: this would only be necessary if there were contact on the inner side (which I really don't think will happen) - and is optional if you want to push the tires all the way out. A 1/4" spacer would be a simple slip-on type that still works with the existing wheel studs, and leaves adequate thread engagement to be safe.
Fit the wheel/tire assembly, check for any inner side contact - and motor on. Oh,yeah, double check the numbers ...

928fan4life

Thanks for the info Garth. If you can, could you post a pic with your new rims on the car once you get them? I just bought mine and should be getting them soon but I still have to go out and get tires for them yet. I guess the rears are pretty much bolt on as well. 1/4" I guess really won't make that much of a difference...even for looks wise.