fc-racer

I was at Weissach Performance today to get a brand new set of S-02's mounted on the turbo in 17" size. While there, the parts manager and I came to consensus that the stock 17" wheels looked silly on my car since it's lowered so much. They sit so far in in the front, it does really look cheap.

So, 18" wheels to the rescue, but which ones? I want the 3.6T wheels, but I want to research more before I buy them, I'd prefer factory parts over RH wheels, especially for the money RH wants for their wheels.

They had a set of 18" Technology wheels taken off a C4S. We mounted them up, front and rear. The front fit perfect, but the rear stuck out about 0.75" too far with 285 tires. He then found a set of Technology's off a narrow body 993, also a takeoff (customer went with RUF wheels). Trial fitted those and they sit further in by 25mm or approx. 1". Should be perfect I think.

I'm not normally a fan of mixing generations when it comes to parts, but the price was right, it looked 100x better than my "lost in the fenders" in 17's and with the lowering, they fit just perfect with almost no air between fender and tire top.

I decided to go with the 265's to ensure that they don't rub and/or look silly and 225's up front. The S-02's come in tommorow.

When all is mounted, I'll take some pics with my new digital camera and post them up on my site. I'm finally starting to get really excited about this car!

Farzaan

JBH

My suggestion is to stick with a wheel design from your model, which really means the C2 Turbo, 3.6 Turbo, RS, and Supercup. Each of these wheels is made by a manufacturer for Porsche, so Porsche only rebrands and charges a substantial premium.

I am pretty the RH 3.6 Turbo wheel is the same as Porsche factory at less than half the price.

The technology wheels are nice, but to my eye (maybe to my eye only)they belong on the 993TT and would look odd on the 964 Turbos. Having said that, I would like to see a picture of your car with the new wheels.

Here is my car with 18" 3.6 Turbo wheels and Bridgestone SO2s (225/40-18 upfront and 285/30-18 in back). See what you think

fc-racer

JBH, no doubt that that the 3.6T wheels are the way to go, I will be the first person to say that, but at this time, I'd rather spend the money on other things that I feel the car needs more, these are an interim solution With the difference between the 3.6T wheels and the Tech wheels, I can almost swing for the RS flywheel and clutch, which I feel this car badly needs to wake it up.

I intend on using the tech wheels as track wheels in the future or I might just sell them, probably for pretty close to what I paid.

I don't think they look "right" on the car, but they do look a heck of a lot better than the 17" wheels which were completely lost in the fenders once the ride height was lowered.

Having said all that, I'll post some pics for everyone to see. I'm open to criticism, in fact I encourage it, it makes for good innovative thinking. I hadn't seen anyone use the 18" variety, only the 17" tech wheels on their 930's which I feel is too small a diameter for that style wheel.

fc-racer

mturo

The 3.6 wheels look very nice! Are there any issues on mounting to the 91 Turbo?

Adrian

Guys,
This thread can be found already answered on this forum and others.
The 3.6T wheels DO NOT bolt straight onto a 3.3T. The rear offsets are different. They are also 10JX18. The 3.3T has an offset of 52.3mm and the 3.6T rear wheels are 65mm offset.
The 3.6T wheels (genuine) are manufactured by Speedline for Porsche. They are VERY rare to find a genuine set and if or when you do the price will be VERY high.
Ciao,
Adrian
911C4

fc-racer

hmmm.... the rears I'm putting on tommorow are 10x18 with 265/35R18 Potenza S-02's. They are a 65mm offset. The 40mm offset stuck out too far, the 65mm looks like it will work. If this works tommorow, I would see no reason for the RH/Speedline 3.6T wheels not to fit.

What had changed from the 3.3T to the 3.6T for you to make that comment?

Farzaan

Patrik S

Adrian,

I´m not sure I understand what offset is.

Is it a measure from the outer edge of the rim to the back of the hub(the joint surface)?

If so, then there must be a different offset if the wheels are wider(9->10) and you want the same distance to the inner edge of the rim. I assume Porsche do not want to extend the wheels closer to the innerbody. The only way left is out!
Am I still on the right track?
Then, if the only difference is 13mm on the outer egde, why is this a "DO NOT bolt straight onto"? And what should be done to make the genuine 3.6T wheels fit to a 3.3T?

/Patrik, 911 Turbo 1991

Adrian

Dear Patrick.
The easiest way to explain the offset numbers is this.
The higher the offset number the closer the wheel will be to the inside of the wheel arch.
The 964 Turbo (3.3) has a standard wheel offset of 52.3mm. This wheel sits xmm distance away from the inside of the wheel arch. If you install a wheel of the same width but with an offset of 65mm, the new wheel is going to be 12.7mm closer to the wheel arch (and the oil lines) than before. Now if you add an extra 25.4mm (1 inch) in width, the new wider wheel is going to be in this case 25.4mm closer to the inside than the original 52.3mm wheel.
An offset of zero means that an equal amount of the wheel is on either side of the mounting surface.
If you want to install 10JX18 wheels onto a 3.3 Turbo you need to reduce the offset to keep the wheel away from the inside. However you cannot install say RS 3.8 wheels because they have an offset of 5mm and these will impact your fenders. Will come out far too far.
If I remember correctly the RUF set up is 43mm front and 48mm rear for their 18 inch wheels. Something like this, they have a number of combinations.
If you wish to run 65mm rear offset wheel you will need to install a 12.7mm spacer on either hub minimum. 15mm or 17mm is normal to account for the extra width.
Also keep in mind when you change offsets you can also change the track front and rear and the front and rear track relationship. This can have a major impact on handling. Sometimes good and sometimes not so good.
You ask about only 13mm Patrick. If you ever see my C4, I will introduce you to what only 13mm means in the form of damage. It is not pretty and I have seen much worse. Static distances and dynamic distances are also important. Body roll can eat up 13mm very quickly. As can suspension travel, camber settings etc,
Ciao,
Adrian
911C4

JBH

Adrian:

Your explanation of offsets was very good and hopefully helpful to those seeking different wheel/tire combinations.

Now...the issue of the 3.6T wheels directly bolting on to a 3.3T. The additional offset on the 3.6T (12.7mm) is exactly equal to one-half the increase in wheel width in going from the 9" wide 3.3T to the 10" 3.6T wheels(1" = 25.4mm). Assuming the increase in width is really carried across the entire wheel, then one-half the increase in width is on the inside of the mounting surface and the other half is on the outside of the mounting surface. Therefore, the 12.7mm increase in offset of the 3.6T wheel is exactly what is need for the added width of the wheel. If this is true the 10" wide 3.6T wheels should mount perfectly to the 3.3T. Am I missing something?

Also, I thought the body dimensions of the 3.3T and 3.6 T were the same so it would also make sense that the two wheels should be interchangeable.

I apologize if I am causing confusion - just trying to reconcile the explanations.

Patrik S

Thank you Adrian!

I found a link to a site with a good picture.
http://www.rx7.org/Robinette/wheel_offset.htm

/Patrik

fc-racer

I got the Technology wheels put on, 18x8 and 18x10 with 225/40R18 and 265/36R18 respectively. I was a bit leary of doing this, mixing generations and all, but I have to admit that the car looks damn good For the price I paid and even if I had to pay $1-2k more, it's still worthwhile.

Nothing rubs at all, even in the extremes. The car rides surprisingly better than with the 17's and the car seems to accelerate better (indicating the combo is lighter than the 17" combo I had).

I am a happy camper. The only downside is that, in hindsight, I should have put on 285's in the rear as the rear fender is still not completely filled out, it could have easily accomodated the slightly wider tire and it would have looked a bit better. Regardless, I didn't want to ask Weissach Performance to make another change. The poor guys previously special ordered a set of 17" S-02's for me and I didn't take them

I'm a happy camper. This car is finally starting to drive and look the way I expect a car of this calibre to look like. Tommorow, she goes in to get a new dash pad as the factory leather one is slightly pulled in some areas.

The only things left after that are to change the plugs, wires, cap, rotor, fuel filter and steering wheel. Then I add boost (buying an HKS EVC from Imagine Auto) and fuel (Andial) and maybe a GHL exhaust.

Then I'm done for 1-2 years; I'll just drive it all over the place, on the street, the track and in rain and start saving for a twin turbo. I could have bought the twinner this time around, but I've always dreamed of the C2 Turbo so I had to own an original beast, a RWD, rear engine, no traction control, no holds barred monster. Once I get that bug taken care of, then I can get the TT.

With the TT, I have a plan though which made it a bit cost prohibitive at this time. I want to buy a twinner in B.C. Canada, ship it to RUF in Germany. Get them to install the Turbo R kit on it, RUF suspension and the BBS GT-2 style wheels. I'd then take a vacation when it's done and pick the car up from RUF in Germany, drive it around for three weeks, enjoy the car for what it was intended for and then return home to the land of the speed limit.

RUF could then send the car back to me in Canada to enjoy on homeland. A bit dreamy, but if you don't aim, you'll never hit, I say

fc-racer

ps - I'll take pics tonight of the car.

Adrian

Dear JBH,
First little myth to sort out. The internal body dimensions are a tad different between the 3.3 and the 3.6 and different again between a USA 3.6 and a ROW 3.6.
The offset difference between 3.3 and 3.6 wheels is 12.7mm and the additional increase in wheel width 9JX17 to 10JX18 adds an additional 12.7mm.
If you add a 12.7mm spacer to clear up the offset issue but you still have the additional 12.7mm of wheel to deal with. This will leave you around 13mm internal clearance. Now add a 285 tyre and your oil line goes west. Every Porsche is slightly different as well. Are you lowered. Are you using progressive rear springs or straights. Are the springs thicker and the list goes on.
No easy answers just the immortal phrase "Please be careful" it can cost you a lot of money,
Ciao,
Adrian
911C4

PS: The comment "making sense" and using inaccurate data (there is a huge amount of inaccurate data around) are the two quickest ways to relieve yourself of a lot of money when you own a Porsche. Of course the other simple point is. If the wheels were interchangealbe, Porsche would have issued a TSB approving it. As they have done with many other wheels.

fc-racer

Adrian, something interesting is that in my searches and dealings with people, I have yet to find a single 964 Turbo owners who has had any problems with 265's or 285's on the rear of their cars, not a single one. There is even one guy who has somehow squeezed 315's in the rear, but he did modify his fender lip slightly.

Perhaps this is only a C2/C4 issue and not a 964 Turbo issue you speak of??? I am not trying to be contradictory, I value your feedback greatly, it's just that it seems like no one I have spoken to has had this problem. From looking under the car and driving the car over very rough surfaces, there is no chance of hitting any oil lines with the 265 S-02's I have on the rear and I don't think the 285's would be a problem either.

I know from living with Swiss relatives that they are very strict on modifying things on their cars, they only purchase approved tires and only do the mods which the manufacturer specifically recommends. Our driving characteristics and legal requirements in North America are quite different than what I witnessed when I was in Switzerland (which is one of the best and most beautiful countries in the world in my humble opinion). Perhaps you are being a bit conservative?

Farzaan

Adrian

Dear Farzaan,
As long as people are forwarned. I do not care about the "I have no problems brigade". I followed that advice once and so did others and we ended up with damage. Two 964 Turbo owners as well.
What people say in public and in private are also different. "No Problems" privately becomes, "well yes I do have wheel rub when I do this that or the other".
The fact that the rules in the USA are different than here is irrelevant. The 964s are basically the same, the wheels and tyres are basically the same and the damage which can result is basically the same. The problems rate is around 1 in 4. You might speak to people but I have interviewed people for my book. The stories are quite different. Plus I use a lot of data from the manufacturer as well.
If they fit, good on ya. If they damage your Turbo, I told you so and be more careful in future. Some you win and some you lose. I do not know how long you have had your Turbo but I have a collegue who installed the RUF 18 inch wheels and had to install spacers to ensure no wheel rub under high cornering forces. Another guy may not have to. However in the end it is not my money and it is not my 964. Not my risk either. However I am not being conservative. This is as much a Turbo issue as a C4/C2 issue and owners or potential owners should be aware of these things. Your right to ignore the advice and the experiences of others. I will always contradict those who say "No problems it fits" because it does not always,
Ciao,
Adrian
911C4

fc-racer

Unfortunately, you have chosen to take my comments as personal criticism, when in fact, I was hoping more for a rebuttal to ensure that this is in fact a problem you've identified on 964 Turbos and not just the C2/C4 line.

As I said earlier, I do value your input. I will, in the future, not attempt to play devil's advocate with your comments.

Farzaan