johnu

Good day all
I have been looking at the wheel fitment charts for the 928 and I will admit I am pretty ignorant when it comes to offset etc.
I am looking at a nice set of cup 2 wheels from a 993 and wondering if they will fit an 87 S4 automatic.
here are the specs:

Fronts 993.362.124.00 ET 55
Rears 993.362.128.00 ET 55

Fronts are 225 x 45 x 17
Rears are 255 x 40 x 17

Would these fit? Would I need spacers?

thanks
John

Gary Knox

Rears are a perfect fit. Fronts WILL fit, but will extend out from the brake rotor a 1/2" beyond 928 spec on each side. Thus, the car will not drive properly. 928 fronts need to be 7.5" wide and an et of 65. Those fronts are probably 7". Rears at 9" wide and et 65 are the same as OE spec on these cars.

jcorenman

What Gary said ^^^. The fronts you want to be looking for are 993.362.124.05.
The .00 wheels were originally fit with 205 tires, too small for a 928.

johnu

That's disappointing. The wheels were like new with brand new tires.
thanks guys!
John

Gatornapper

Gary -

Do you know the widths on my original 16" Phone Dials for my '81 928? I thought they were 7" F & R..........

I have a set of 7" & 9" Club Sports with 65 ET on front and 60 ET on rear that I plan to put on the car. Was told the 9" 60 ET rears would work........

Thanks,

GN

Jerry Feather

You didn't post the widths of the wheels but if they are 7 inch front and 9 inch rear they will work just fine on your S4. The tire sizes are perfect for the 928, right at 25 inches diameter.

Darklands

Here in Germany with TÜV the 7“ Cup 2 wheels haven‘t enough load capacity for the weight of the 928.

Fly911

I'm running 7.5x17ET55 with 225/50-17 and 9x17ET47 (Cup 1 wheels) with 15mm rear spacers (effectively making them ET32) with no issues. The fronts are tight, though....
The 993 fronts are just 7", that is kind of narrow...

Petza914

They'll fit and drive fine. The front offsets are on the lower side 57-65 is the better range, but you're only off by 2mm from what a lot of us run, though the common upgrade width is 8" et57 in front with a 225.or 235.tire.

If the wheels are nice and a good price, get them.

Here's how an 8" et 57 with 235 tire sits. If your prospective wheel is a 7.5" width et 55 it will be 4mm further in and if a 7" wide et 55, will be 10mm further in.

johnu

Yes they are 7 and 9

FredR

John,

Last thing you need would be spacers!

As with most of these wheel threads the question invariably asked is "Do they fit" the question you should be asking is "do they work?".

For sure they wil fit but as I am concerned they do not work in that they will not achieve the design intent. The S4 and GTS models were designed to have a negative scrub radius of minus 10mm. With an offset of 55mm those wheels have zero scrub radius. The 10mm NSR they are designed to have can ionly be achieved with wheels that have an offset of 65mm unless the hub is redesigned. The NSR is a passive safety feature in that if the car hits a surface that induces yaw the steering will tend to carry on in a straight line rather than crab and induce a spin. Such can happen if one is unfortunate enough to hit standing ater on the side of the road for instance. The chances of having such a problem are very slim but it can happen- it happened to me and I live in a desert climate- came flying into my favourite bend one day and was horrified to see watter all over the road due to a burst water main- my front wheels are ET68 and the car literally sailed through it without batting an eye lid. Going sideways at 100 mph and about to hit a tree midships is not a good time to realise that the Porsche engineers actually do know what they are doing. I beleive it is this feature that gives the car its inherent feeling of stability. For folks tracking their 928's it is probably not a welcome feature and handling is probably best optimised using a small positive scrub radius but then racers generally do not drive in floods!

The irony is that even Porsche were all over the place on this one in that the likes of the 928CS, 928SE and earlier GT's have a front offset of ET60 and this conundrum has never been explained to my knowledge. I personally would not run a street 928 without the correct front offset but each to his own as it were.

As for the wheel width that tends to vary with diameter- a 16 inch wheel as on the S4 with a 225 section is optimal with a 7 inch width- hence what we see fitted to the S4. For a 17 inch wheel running a 225 the optimal section width is 7.5 inches hence what we see on the GTS models. My front wheels are 9.5 inches ET68 and run with either a 255 or 265 section depending on what I can find at the time!

jbrob007

What Fred R said ^^^^^... I had the wrong offset wheels on my 84 and while they were GORGEOUS they were a handful at speed with uneven road. I wouldn't do it again.

johnu

Thanks for the replies. I am running some Simmons 17s that came with the car (rears have spacers). They are in need of tires due to age. I am thinking I might just have the original manholes refurbished and put those on since I need new tires anyway.

Petza914

Yep, I swapped those to eliminate the rubbing and improve the handling.
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928GT8108

My previous CUPII setup is 17x8 (ET70) Front & 17x9 (ET55) Rear