sharknose

I'm told OEM wheel specs for 91 928 GT are 7.5"x16 65 offset front, 9"x16 52.3 offset rear.
I'm having a hard time finding 1991 DT90 (Design 90) wheels. The attached link is for Porsche wheels which are 8"x16 52-55 offset front, and 9"x16 52-55 rear. So the rear wheels should be fine, the question is the extra half inch of wheel width and the 10 mm offset difference in front. I would also probably be giving up the TPMS.
Here is the ad:
https://sandiego.craigslist.org/csd/pts/6036191825.html


Anyone know where I can get the proper OEM Design 90 wheels? I prefer Chrome or polished.

Rob Edwards

Those are arguably better than D90's would be, those are forged clubsports, albeit kind of ruined by having been chromed. They will fit fine, sounds like the fronts started as 8" 928 rear Gullideckels that got the slots cut out to look like Clubsports.

If you want D90s, 928Intl might have a set- give Tom a call in the AM.

FredR

Something here does not quite add up. When I see the terms "modified" and "928 wheels" in the same sentence it worries me - what modifications and by whom?

Regarding offsets what do they mean by the term 52-55? They are one or the other [or neither] but not both. If they were modified they were done so to suit a 944 not a 928. I am aware of 8x16 inch 928 wheels that have an offset of 52.5mm that come from the rear of the S4 and there is the excellent Clubsport wheel which is 8x16 with ET60 so I would want to know how exactly they ended up as they are "advertised".

Assuming the fronts have somehow ended up 8 x16 inch ET55, as you rightly say the 928 was designed for front wheels with ET65 to maintain the negative scrub radius intended. There is an anomaly that I do not understand in that the 89 GT model was supplied with the ET60 forged clubsport wheels - for that year only. Thus the question becomes not "will they fit" but "will they work?".

Lots of folks run with wheels that do not meet Porsche criteria and report no issues and for most the offset seems a minor or non issue, some of us believe otherwise. I take the point of view that going sideways at 165 mph is not the time to find out one "made a mistake". Most owners have probably never been at such speeds in a straight line never mind in bends.

Many family saloons can hit 120mph these days if pushed but they are a "white knuckle ride". You can do this in a 928 reading a book it is so relaxed [not that I am advocating this] but there are reasons why this is the case.


Rgds

Fred

DeWolf

Oh come on man.....where's your sense of adventure

VT928

If I remember correctly there was a time when people wanted to have the Club Sport look without the cost of the actual CS wheels. They would have the factory slots milled out to match the look of Club Sport wheels.At the time the CS wheel cost about almost a $ 1000 per wheel

FredR

Having gone into a wall at 70 mph and losing my beautiful 90 S4 because of some tw*t on a mobile phone puts things into perspective somewhat!

I do believe there is a fine line between "being adventurous" and being "downright stupid" and when making modifications to what Porsche specified one has to be pretty sure one knows what one is doing. Most of us come a long way behind in the knowledge stakes thus when it comes to modifying things I like to feel confident that the proposed mod has been well proven as in competition events and the like.

Tyres/wheels, suspension and brakes are the most safety critical items on any car and going "cheap" on wheels for a 928 does not sit well with me.

Rgds

Fred

Randy V

Why bother with 16" wheels? The tire choices are very poor and expensive.

Your sig indicates you don't currently own a 928 - what will you be using these for?

sharknose

Guys, thanks for all the great input. It is very much appreciated. I will give 928 International a call. I have become obsessed with owning a 928, the more research I do and the more i like what I read. I drove a 91 GT and now I have the bug.
I have been shopping for the right 928 for 6 months and I have narrowed the search to two different 91 GT's. One of them is presently listed for sale on BaT, but that sale price could go higher than I want to spend for a car I see some shortcomings with. I'm looking at it in person Sunday afternoon in LA. Anyone want to guess what they think that car will sell for Monday afternoon on BaT?
Regards,
Charlie

jcorenman

I'm no good at guessing, but I would advise a careful look. The D90 wheels are correct but the 8" rears are not... very odd. Intake paint hasn't been refreshed, yet car was repainted and interior redone, that seems odd. Bling radio, amp instead of spare, cheap tires, cats hacked out instead of x-pipe ... not faults necessarily, everyone has different priorities.

Good hunting!

sharknose

Jim, I drew some of the same conclusions. Why change the paint from black metallic to standard black when re-spraying? stupid move imo. As you point out, the exhaust decision also seems short sited. I will say that to my eye, that interior is stunning, imo, the white & black looks so clean and contemporary it really goes well with the 928's lines. Don't you think that complete interior must of cost around $8k - $10k even in a low overhead LA sweat shop? I'm the high bidder on it right now against my better judgement.
Thanks again for the input.
Regards,
Charlie (PlanC)

928Collector

For a 91 GT I believe:
16 inch rims an ET/Offset of 60 or 65.
17 inch rims only an ET/Offset of 60 will work.

LZ bolt pattern is 5 x 130 for both the 16 and 17 inch rims.
Diameter / Center Bore of 71.6.

Please advise if you know differently?

928Collector

For a 91 GT I believe:
16 inch rims an ET/Offset of 60 or 65.
17 inch rims only an ET/Offset of 60 will work.

LZ bolt pattern is 5 x 130 for both the 16 and 17 inch rims.
Diameter / Center Bore of 71.6.

Please advise if you know differently?

Rob Edwards

Stock fitment on 91GTs only came with 16" wheels, fronts were 7.5x16 ET 65, 9x16 ET 55, with the 5x130 bolt pattern. You could mount an enormous range of 15-19" wheels on a '91 GT, it has rolled fender lips and plenty of room in the rear for larger than stock tires. Keep the offset up front greater than 55.

FredR

The 91GT was supplied with Design 90 wheels and the front rims were 7.75 inch wide ET65 - Porsche part number 928.362.114.05 as per my data.

The 89GT was supplied with forged mag alloy wheels that were originally fitted to the CS models wherein those front wheels were 8 inch ET60. Why Porsche found it "acceptable" to reduce the negative scrub radius on the wheels supplied with the CS, SE and 89GT remains something of a mystery that I have never seen explained in a manner that makes sense.

When it comes to wheel fitment there are two concepts- "will it fit" and "will it work". Most owners historically appear to focus on the former whereas I reckon the latter is more important. The NSR [negative scrub radius] concept is a passive safety feature designed to ensure the car retains optimum stability in the event it hits a condition [on the road] such that if there is a differential drag [side to side] the car will still tend to maintain a straight line trajectory. This is the intent behind having a wheel with ET65 that has a NSR value of 10mm. The ET60 wheels have an NSR value of 5mm.

I have a feeling that the handful of 928 wheels fitted by Porsche with ET60 were a bit of a trade off- why they were supplied this way only Porsche appear to know. I get the impression that folks look at the offset and rationalise that ET55 is "almost" the same of ET65 whereas perhaps they should compare NSR values of 0mm versus the "correct" value of 10mm.

In reality chances are owners will never see a scenario wherein they will regret not having the correct scrub radius and any owners that "wrecked" as a result of not having such feature are invariably going to be oblivious to the fact anyway.

Ignoring what Porsche designed into the car or worse, assuming it has no value is a somewhat foolhardy approach. A track car is not likely to have a problem with standing water but a 928 hurtling down the autobahn at 150 mph can hit a band of rain and be well into it before they even know what hit them. Features like this and the Weissach axle are what make the 928 so outstandingly safe when pushed along hard.

puyi

ET 60 vs ET 65 is all about handling. ET 60 is the best choice for optimal road behavior while ET 65 is better for easy handling. The technical explanation is that the axial pivot is aligned with the center of the tire in contact with the road, while ET 65 causes an offset to the wheel of 10mm which facilitates the effort at the steering wheel.