etom

There is a local set of these, and have thus far resisted.

DaveK

I would be surprised. Although I know a lot of people are fitting 18s these days I clearly remember posts in the past saying Porsche advised against fitting 18" wheels to 964s.

Computamedic

AFAIK the 18" "Speedline for Porsche" wheels were standard fitment on the 1993 3.6 Turbo cars although the wheels you have pictured are NOT those. The wheels in the picture are Speedline Alisio which are an aftermarket wheel, very similar to the 3.6 Turbo wheels albeit with the elongated stud holes. The 3.6 Turbo wheels have round stud holes.

Fitment of ANY 18" wheel to a non-Turbo 964 is officially prohibited by Porsche although, as Dave says, many owners (including me) are fitting 18" wheels with no apparent ill effects (yet).

Regards

Dave

OllieW

I fitted 18" split rim replicas to my RS and was told that they will be absolutely fine as the car ran them in the race series. With a non-RS model the issue is with the additional load on suspension mounts, where they can crack and fail.

As Dave mentioned though there are lots of std 964's running them and have had no problems...

kurquhart

I had Speedline Aliseo on my 90 C2 with only the steering rack brace upgrade; no problems.

MitchB

I would love to have someone explain to me why an 18 inch wheel setup is bad.

If the combined wheel / tire weight is the same as a 16 or 17 (and with modern wheels it can be), and has the same rolling diameter - how is it different?

The Porsche "recommendation" - as I've read - is no more than a statement for the lawyers, because they didn't test and or certify any 18 inch fitments on these (NB) cars...

Computamedic

Mitch,

I don't think you're alone in your thoughts. I tend to agree that the official statement smacks of protection against the litigious nature of the US mentality but I beleive there are some undeniable facts that may help to perpetrate the myth.

18" tyres certainly have much stiffer sidewalls than 17" and, as such, will transmit more shock forces to the wheel, and hence suspension. There is some evidence that these higher shock loadings will affect the suspension and hubs although there is little evidence to suggest failures are experienced because of it. Certainly Cup cars in the early '90s were running 18" wheels, albeit with slick tyres and they DID experience some failures but the loads under racing conditions are somewhat greater than any road use is likely to generate.

There was also a story I saw mention of some time ago about the proximity of the cat converter to the rear left tyre being a reason for potential failure - more because of the additional width of a 18" tyre than purely the diameter. I'm not sure I can see the potential there though.

This subject comes up time after time and no doubt your question will get a good mixed response - yet again.

Regards

Dave

MitchB

Dave -

Good points. I haven't seen this come up before - glad I'm not alone.

The sidewall issue may have some validity, but these are street cars so I would think it would have been addressed. They are expected to hit an occasional pot hole or two?

I can see where someone would point at racing failures. But those would be more from lateral Gs from the increased grip, no? That would exist independently of wheel diameter.
If increased (lateral) loads were deemed the reason for suspension wear / failure, then the warning should be against using wider tires, or stickier compounds (slicks, R-compounds, etc.) NOT a change in wheel diameter.
My 2 pennies..

YYC930

The only 18" wheel on any factory stock 964/965 (non-race car) was the Speedline wheel on the 3.6 Turbo.

cobalt

This is what Porsche claims. The Cup cars were reinforced unlike the street cars. Porsche made changes to the 94 turbo suspension over the 91-92 turbo to accommodate these wheels. Don't forget the factory also tends to be cautious about what they approve so not to cause them additional expense.

Yes the only modular 3 piece wheel used on a production car was the "Speedline for Porsche" 18 inch turbo 3.6 wheel. This was also used on the ROW 1992 turbo S, Euro cup cars, 3.8RS/RSR and a few 968 turbos. Otherwise the Alessio equivalent of this wheel was used on the ROW 993RS, 993 Cup & 993GT2 other than the 94 turbos these were not considered production cars.

Ag02M5

[QUOTE=kurquhart;5413052]I had Speedline Aliseo on my 90 C2 with only the steering rack brace upgrade; no problems.[QUOTE]

Can you add some more detail on this? Is it the 993 brace? Does it bolt right up to the 964?

Also, did you change out the steering stops?

Thanks

RT

Ag02M5

Kris, do you run a manual steering rack? Looks like it won't fit a standard 964.

kurquhart

Yes, I bolted the 993 brace to my 90 C2 PS rack. See posts 12 and 17 in this Pelican thread for the differences in 993 and 964 racks w/ the brace installed:
http://forums.pelicanparts.com/showt...hreadid=261543

parsecnc4

Are the PS rack the same across all 964/965? Also would you have the part number for the 993 brace as well as related nuts/bolts? Maybe I will do that on mine just in case.

Ag02M5

Excellent info.

Does it rub on any of the lines. It looks like the rack is mounted inside the rubber insert so even if it wasn't touching, I am thinking the lines could still rub under aggressive driving. How close is it if not touching at rest?

Maybe a little grinding would help. Even if it isn't as strong, it would still add some rigidity over nothing.

Thanks.