Rocket Rob

My 90 C-4 cab is lowered and has 17" cup wheels. No problems. My recommendation is do it. It makes the car look great! Rob

Bob Haase

[quote]Originally posted by Adrian:
<strong>...To fix this problem you need to firstly carry out a slight body modification to remove part of bracket... and you will need to install a 3-5mm spcare up front... OR remove part of the steering system and replace the 6mm steering stops with the 1991 model year 10mm steering stops. Spacers is easier and cheaper. </strong><hr></blockquote>


Adrian and others, I hope you can help as I am about to purchase new 17" wheels and tires for my C4. I need some clarification. It sounds like I can cut off some material and add spacers. My other option is to add steering stops which sounds complicated without detailed instructions.

Should I go the other route and add some spacers, how do I cut off the offending material that will rub the tire? Is there a place on the net that has instructions with photos?

Thanks in advance!

Jeff Curtis

Bob, if you're ordering NEW 17" wheels for your 964, I'm assuming you're going to have 7" up front? If so, see if you can get 50mm backspacing vice the common 55mm...that should prevent any rubbing as it will bring the wheel out 5mm more.

Then you won't have to deal with any of this spacing/steering stop B.S.

Adrian

Dear Bob,
The full instructions which are contained in Porsche Technical Service Bulletins can be found at <a href="http://www.alldata.com" target="_blank">www.alldata.com</a> You have to pay a small yearly subscription fee but you get every TSB applicable to your model plus the wiring diagrams. These alone are worth the money.
I can help out privately when somebody is seriously desperate.
As for which is best path to go. Spacers is the cheapest. I run 5mm with standard studs. Porsche and TÜV say 6mm. What I did for a little extra security was to remove the wheel key lock and used an open wheel nut.
My steering stops and the body mod have also been carried out. In the end I would recommend all if you are going to run 225 or wider front tyres.
If you go 50mm front offset I have to disagree slightly with Jeff. The rub depends significantly on the actual or real tyre width, not the technical width and not just the additional wheel width. 5mm is sometimes not enough so be prepared to use spacers with a 50mm offset front wheel if you go 225 or up on the front. 205s are okay. No I do not recommend 215s up front.
Ciao,
Adrian
911C4

Jeff Curtis

I guess what I meant to say is that the 5mm difference in backspacing on the wheel SHOULD cure most rubbing. Yes, the real tire width does come into play, as different manufacturers have different specs, and of course different sidewall "flex" rates.

A 215 series Bridgestone Potenza 730 is about the same width as everybody else's 205s...that's why I went with them.

Adrian, your 5mm spacer does the same job as getting a wheel with 5mm less backspacing - that is what I was attempting to illustrate. That's what I would do, a neater/cleaner setup rather than using spacers.

The rubbing from my street wheels/tires has been eliminated with a 3mm spacer, again, I have 215 series Bridgestone Potenza RE-730s up front, they work VERY well and are about 4mm shorter than 205s, so the front end is really tight at autocrosses and the sidewall flex will be a bit less.

Think about it, 4mm is NOT a lot...so I went with it, especially being that the speedometer isn't measured off the front wheels.

If I had 225s, they would certainly rub and I would have to carry out the steering stop mod. I use 225s on the track and try to limit how much I crank the wheel around when in the paddock...to limit the rubbing, which is pretty bad with 225 series Hoosiers. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

As for 5mm spacers and using factory aluminum lug nuts...people who do that are cutting it pretty close. I wouldn't even consider 6mm!

The reason I say this is for several reasons, the main one being that MOST Porsche owners have fairly worn aluminum lug nuts, let's face it, it doesn't take long to cause wear on the threads of those babies...especially if you change wheels a lot...like I do.

Aluminum lug nuts on steel studs, think about it.

There is ample thread contact with the factory setup, but now you add 6mm, even 5mm into the picture and make the measurements yourself...the threads on those &lt;usually&gt; worn factory aluminum lug nuts are now doing "double-duty"!

If you want a good example of what I speak of, get a couple steel lug nuts, the kind you would use on the track, put a 6mm spacer on, then the wheel...tighten down the lug nuts and look at the open-ended steel nut to see that your stud ends about 3mm INSIDE of the lug nut - not good.

I am horrified when I walk by people's cars at the track and can see, just from walking by that they don't have ample stud length.

Mind you, the PCA Club Race guideline says that they approve a scenario whereas the thread contact has to be the width of the stud...so with 6mm this actually passes - BARELY.

Now we have people doing this with ALUMINUM lug nuts and they deem that to be safe?? That makes me question TUV standards.

I, in no way want to start a war with opinions over TUV standards, because in the U.S. there is no inspection guideline that verifies stud length/approved spacers THAT I KNOW OF. Just put yourself in that previous scenario and consider how long your aluminum lug nuts have been in service, how many times they've been torqued, removed and retorqued and ask yourself if you think that's safe??

I use 3mm spacers up front, this is "okay" in my book, but still not an ideal scenario...but I live with it, that 3mm difference in thread contact, when compared to using a 6mm spacer could mean all the difference in the world.

I use 6mm spacers on the rear, but have extended my studs 12mm for proper track wheel backspacing and passing guidelines for thread contact. I use 12mm worth of spacing with my track wheels because they're 275 series Hoosiers. I leave the 6mm spacers on for the street because I can still use my factory aluminum lug nuts (new, BTW) without them bottoming out and not tightening down the wheel. Without the 6mm spacers they bottom out.

This is my rant, let me have my rave...just consider the scenarios I've painted and think for yourself. I've done A LOT of research in this department...and have witnessed a wheel coming off a 911 at the track - NOT GOOD! His SPACER came off too, a 6mm one...no extended studs, using aluminum lug nuts.

Look for a simple procedure to install extended wheel studs in a certain publication that will appear on the market in the near future.

I'm sure it cost him, or his insurance company at least 5K...it could've cost his life.