tafkai

dont forget that the rs has different front hubs / rear susp. etc. to a normal c2 .
so i dont think you can say there problems are ours , or our problems are theres !!!

i think its more to do with type approval .
is the engine safe for over 300 bhp in standard trim ? yes .
so why did porsche only offer it with 260bhp max ???? (rs)
my car came with the official option 17" cup1's . no problem ................
i've now fitted 18" speedlines from a cup racer ............ no problem

dont forget ..... warranty issues , and in america court-case issues , that might arise if everybody fitted 18's to there new 964 , and chipped it to 300 bhp , then something broke !!!!!!.

Gary R.

My 18" Fikse's/MPS2's are SUBSTANTIALLY lighter than the D90's/Pirelli's were and are almost exactly the same rolling diameter. They are the proper offsets (no spacers) and being LESS unsprung weight I can not believe there is the slightest problem using them as long as they don't physically interfere with the suspension or steering travel.

Jeremy Pinsly

Gary, I agree with you....My previous comments were directed at wheels that were heavier due to increased size. Lighter wheels should not cause a problem.

VgP964

back to Don's original question. I have Ruf 18" speedlines....no issues or problems.

Gary R.

Wasn't directed at you Jeremy, I just wonder what the heck PAG is thinking...

JasonAndreas

The 1993 Supercup and 1994 Cupcar suspension components are all completely different (the wheel carriers were 964-331-065-70 and in prior years they used 17" wheels). I can't imagine PAG would have gone through the trouble and expense of issueing a TSB, warning about a potential problem and actually writing that they noticed the issue during long term testing and only have the problem happen with slick tires and suspension components not really available to the public? Just about every other TSB warning they've issued has happened to myself and/or somewhere here on Rennlist! How many people with 18" wheels have actually driven 15-30k miles and then checked all their suspensions components for cracks?

I realize Adrian doesn't speak for Sportec but I too would be interested to know why it is okay to use 19" Sportec wheels. Is it because they didn't notice problems during any long-term testing that may have been required for TUV approval? If that is the case than we can't make the jump that its suddenly "okay" to use other manufacturers 18" wheels. (not that anyone appears to care)

ttAmerica RoadsterAWD

My two cents: I've also 18 inch wheels. Objectively speaking, I've done some research as to why the 3.6 turbo CAN have 18 inch wheels, but not the 3.3t nor 964's. I went straight to the Porsche PET and saw that the only difference in part numbers between the 3.6turbo and my "turbo suspension" 964 is: 1. different struts/shocks, 2. different carriers (uprights). Rear seems to be same standard issue with mine.

That said, I've not had any problems, but I did changed struts to JIC/Cross.

Jaime

CraigC

I have Tech Art 18" wheels on my 964 C2 with Dunlop Sport 9000 tires. I believe it has traveled about 30,000 miles on these wheels. Ive been all over the suspension and found nothing wrong. The wheels and tires are somewhat heavy but then I dont really know the weight of other wheel and tire combos.
My tires are 225 40 18 front and 265 35 18 rear. Weights are 45# front and 50# rear as measured on my digital bathroom scale. I would be interested in knowing weights of others tire & wheel combo.

A pic of my car:

Oddjob

There is a similar Factory tech service bulletin issued with the same warning about putting 18" wheels on any 944 series car. And periodically some urban legend warning of catastrophic failure surfaces on the rennlist 944 boards regarding 18" wheels.

I cannot speculate as to why the Factory did this. What I can say, I have been playing with these cars since '92 and have tracked and raced four different 944s over the past 14 years. I have seen a lot of 911s and 944s running 18 wheels at the track, and running them hard.

Any tracked or raced car will experience some accelerated wear and fatique on many of the mechanical parts. But in general, I have never heard of or seen any suspension failure that was caused by, even in part, by a larger diameter wheel.

If anyone has some first hand evidence of any type of suspension failure that can be attributed to an 18" wheel, please post it.

Otherwise, my belief is that there is no problem running 18" wheels on a 964.

Manny Alban

I run 8 and 10" 18" wheels on my 1990 C2. The car is 95% track and 5% street. The first year I had the wheels, I went through three sets of wheel bearings. I had used the original bearings for 150 track days. I didn't think anything about it when they first went up. Figured they were old and used and needed to be replaced anyway. After the second set last two track days, we knew something was up. We placed the hubs as a safety measure. Those bearings last a few more track events. My mechanic ended up replacing the C2 hubs with C4 hubs. I believe these bearings that are for the C4 hubs were bigger/heavy duty compared to the stock C2's. Since then I've had zero problems. It's been about 60 track days. Everything else was fine. I've spoken to other people who run 18" wheels on the track and they've had zero problems. Maybe it's just luck. Either way, I'm glad my problem was solved because I really love the 18" over the 17" for the track.

ttAmerica RoadsterAWD

Jim B. 944turbos do have propensity of lower control arm failures! Usual place of fracture is at the ball joint-control arm body section. I use to have a 944t and replaced the control arms with fabcar aftermarkets. If you were going to race a 944t, it was required to change out to motorport ones or Fabcar.

Jaime

Adrian

Firstly the 19 inch wheels fitted to my car were specially designed by Sportec and built by BBS specifically taking into structural issues with not just the 964, but the 993 and 996. Their individual unit cost shows the amount of R&D that went into these wheels.
These wheels have been approved after extensive testing by both the Swiss and German authorities. They are NOT approved by Porsche and nor can their fitment be regarded as an approval to fit any other wheel to a 964 or other Porsche for that matter.

To the best of my knowledge Sportec is the only wheel designer/manufacturer which actually went and did these tests directly related to the 964. They used my C4 and a 964 RS.

These 19 inch wheels are of a significantly different design to the standard 18 inch wheels. However regular inspections are carried out to inspect for related damage. For more information contact Sportec because I do not speak for them as Jason points out.

From a personal point of view I would NEVER have had these wheels fitted myself if I had to pay for them. On a 996 no problem, but not on a 964. They only remain on my car because they are approved, it didn't cost me anything and I am interested in detecting any long term problems if they exist.

Getting back to the 18 inch wheels. PAG do not approve 18 nor 19 inch wheels on the normally aspirated 964s and this is explained in my book.
964 Cup cars bear no resemblance to normal road cars, yet it was structural failures on the 1992 Cup cars first fitted with 18 inch BBS racing wheels that brought the problem to a head. Wheels were flying off the front and rear with almost reckless abandon here in Europe. In fact it became a bit of joke among the other competitors.
There was also weakness discovered on 1990 model year C2s up front with 16 inch wheels which required a TSB and a fix. I was told that this wheel carrier problem was always on the mind of Porsche from that time onwards.
Later extensive testing carried out by Porsche on their Weissach test track show that the front wheel carrier mounting systems could not handle the extra load placed upon them by the wider wheels.
Whether any owner wishes to follow this advice, the approvals or TSBs it's up to them, the owner always takes the risk.

One last point. The bigger the wheels the bigger the tyres. The bigger the tyres the higher the replacement cost. The bigger the wheel the more of curb magnet they become.
From purely a cost issue I would stick to the 17 inch wheels on the 964. Maybe paint them in the body colour if looks are that important.
Ciao,
Adrian.

PS: In some countries the fitting of non approved components can impact your insurance coverage. Switzerland is one such country. In fact it is illegal to fit non approved wheels anyway. The Police can pull you over and defect your car for this. Ask me how I know?

MARC A. 964 C4

Adrian, thanks for a clear to the point explanation... I’ll say good-bye to my 18" BBS's that I was contemplating on buying one of these spring days to come... Painting my 17" Cup wheels sounds even more original. Should by chance you read my post,. What do you know about polishing existent 17" Cup wheels to an almost chrome finish, and can you if allowed, actually recommend a wheel re-finisher in or abouts your part of the world... I’m unable to locate anything related to wheel polishing in the Cannes/Nice locations...

An 18" Sportec and built by BBS sounds good though, Where would one find the information, available models, and how much is expensive... All good questions if you could please...

As usual thanks from an enthusiast,
Marc A.
Mougins, France.

Christer

I think the fact that the Sportec wheels were tested is fair enough, but what were the results of that test? How wide are they? What rubber is used? If an 18" wheel is lighter than a 16" wheel then I am sure that the wheel istself is not going to cause a problem, but the wider rubber fitted will of course provide more grip (and more weight than the smaller tyre) and impose greater forces. I think if the Sportec wheels have been approved then we need to know the weights of the wheels and the sizes of rubber used. If ANY wheel one is considering buying have less weight and do not use wider rubber then I would just go for it....I mean what other variables are there unless the Sportec wheels offer suspension support in which case I would like to know how that would be achieved?

Oddjob

Sure, but ball joint failure is not related to wheel diameter. Plain 944 n/a's with 15" wheels can and have broken ball joints.

'86 Turbos have had some problems with actually breaking control arms when using weltmeister sway bars and excessively lowered, but 87 and later control arms do not break. The problem is just ball joint pin. The factory motorsport arms (I have a set), are the same casting as the 87+ control arm, the ball joint pin just has a slot for the pinch bolt, not a groove around the whole diameter of the pin.

By enlarge, the balljoint failures happen when the joint is worn and there is excessive play. If you dont check and replace the control arm when the balljoint is wornout, then you are taking a risk. If you dont want to worry about checking the balljoints often, there are several aftermarket suppliers that make control arms that are approved for use in PCA Club Racing - however there is no requirement to replace the factory control arms.