Claimchaser

Hello guy's
I have the chance to get a set of 17x7 & 17x9 wheels froma 993.I was wondering if the offsets would be ok? Will these wheels look right on my car? They seem to be a good price $600 a set,with min.scratches.Would I need spacers or will they fill up my wheel wells.Any suggestions on an aftermarket?

Ed Ruiz

Although some have done it, the 993 7"x17" front wheels are a bit narrow for the recommended 225/45-17 tires that should be used. The 928 GTS 928 size for the front is 7.5"x17" and 9"x17" for the rear.

I purchased 993 Cup wheels several years ago, but in my case the front wheels were 8"x17" and the rears were 9"x17". The 8"x17" was a factory option, that a few 993 owners were willing to get. I now have 235/40-17s on them.

Jay Wellwood

Hey Claim....

I have the 993 Cup wheels on my '87. My car came with them and 25 mm rear spacers. The fronts fit fine w/ noproblems. The rear spacers were 'shaved' in order to get the proper clearance. I think they measure about 5/8 inch now.

In as far as price is concerned - $600 for a used set might be entertaining - depending upon condition (scratches and potential bends). I'd recommend checking them very carefully/thoroughly before purchase.

BTW - seems like Tire Rack is having a sale on these type of rims right now - and I seem to remember 928 International saying they could let a new set go for ~$875. That being said - $275 for new vs. used (and possibly bent with scrathes) may not be a bad way to go.

Ed Ruiz

The following comes from the DEVEK Q&A section.

"How does the ratio of rim width to tire width affect performance?

Of utmost importance is matching the rim width to the tire section width. A wheel to tire ratio of .88 to 1.0 is desirable for predictable wheel/tire performance and sidewall behavior. Too wide a tire on too narrow a wheel, for example a 275 on a 9" wheel, yields a ratio of .83 which will produce unpredictable sidewall behavior."

With this as the guide, a 225mm tire on a 7" rim will have a wheel to tire ratio of 0.79 (177.8mm/225mm = 0.79) Clearly, that's too low a ratio according to the folks at DEVEK.

Given that the 993 7"x17" wheels were already available, one should wonder why Porsche didn't use 7"x17" rims as OEM equipment on the GTS. They didn't because 7.5" is safer. YMMV.

jim morehouse

Ed,did they have 225's on the 7.5" rim? Unless I'm doing something wrong, that gives you a ratio of only .84...still below the Devek guideline. Or did Porsche have narrower tires on the GTS?

Totally different question: I picked up the 91GT project car on Monday. It's got 16" design 90 chrome rims...I thought the GT's came stock w 17"? Or do you only need to go to 17" in order to use the GTS calipers? I'd read the manual but,alas, the car didn't have one with it....I seem to recall someone selling these, do you know who?

Jim

Ed Ruiz

Both the GT and the GTS came stock with 225mm wide tires mounted on 7.5" rims. They may not be as safe as the DEVEK folks would recommend, but they are safer than 7" rims.

The GT's came with 7.5"x16" front rims and 9"x16" rear rims. If you install GTS calipers you will have to go to 17" diameter rims. Also, the RDK system will be rendered useless.

W.A.Mozart

Interesting ... '87 S4 came stock with 7" front wheels and 225's. This is factory spec, per 928 specialists:
87-89 S4 7x16 / 8x16 225/50-16 245/45-16 Flat "Disc" F-65/R-52.3

Ed Ruiz

The 7"x16" wheels were able to safely support 225/50 tires because the tires have a 50% aspect ratio (225/45 will not fit properly). When they went to the 7.5" x 16" wheel (GT), the car became less prone to understeer, which is actually less safe from a manufacturers point of view, but sportier from a driver's point of view.

When the GTS went to 17" rims, the front wheels had to be 7.5" to safely accommodate 225/45 tires. IMO, 8" x 17" would have been better (and in fact, that is what I did). YMMV.

For proper tire fitment, talk to a real wheel/tire expert, not the guy behind the counter who just wants to sell you tires. I'm fortunate to know several such experts. I'm sure you can find some as well. If not, give either "DEVEK" or "Wheel Enhancement" a call.

Chris Lockhart

Ed, et al, my '89 GT came with 8x16 front and 9x16 rears, not 7.5 fronts.This was listed on the original window sticker which I still have, although I never measured them myself. Was this changed on the '90 and '91 GT???

Ed Ruiz

Dear Chris:
I should have been more specific. You are correct. The 89GT was the only year that came with 8"x16" front wheels. Moreover, they were the last year that Porsche put forged wheels on the 928.

For these two reasons, they are highly prized and rather expensive, as you probably know. The GT series in 90 and 91 got 7.5"x16" cast wheels up front and 9"x16" in the rear.

Due to larger front calipers and rotors, in 92 the GTS got 7.5"x17" cast wheels up front and 9"x17" in the rear. YMMV.

Chris Lockhart

Thanks Ed. I didn't realize that they had changed the width. I thought they had just switched from forged to cast. The replacements are a bit pricey huh??? If my memory serves me correct, they were around $1200.00 per front, and $1400.00 per rear. OUCH!!!!!!!!! That's why I wnt the aftermarket route. More in my budget range. Take it easy.