BGLeduc

OK, I did search, but did not find this specific topic.

Can a factory design 90 in a 16x8 size work in the front of a C2? I am thinking yes, but would welcome any and all comments.

Per Adrian's book, a 225 tire will fit in the front of a 964, with steering stops and minor body modifications (per the procedure in the Porsche TSB for 17" wheels).

I can confirm that, as I actually run a 225/50 16 as a autocross/track tire on the 16x6 D90, and while it fits on the rim, it does bulge a bit. Obviously, a wider wheel would be a better choice for that tire.

Again referring to data in Adrian's book, the factory offset of a 16x8 D90 is 52.3mm, while the 16x6 is 55mm. Assuming my math is right, and my understanding off offset is also correct, all of the extra width of a 16x8 wheel is outboard of the mounting flange.

EDIT: The preceeding statement is false. See correction later in the thread!!!

So, I should not have any issues with tire rub on the inside edges of the wheel well, and should be able to get by without spacers and longer studs.

Right?

And with D90's available at almost give away prices, I think this would be a good upgrade for track/autocross purposes, short of doing 17" wheels, which are not on the horizon right now.

BGL

Adrian

Dear Brian,
With an 8JX16 up front you might have some wheel rubbing issues at full lock. You may need to use a spacer but the only way to find out is to try it.
225 tyres are a good fit on 8Jx16 so there is no problem there.
Let us know how you go,
Ciao,
Adrian.
964C4

PS: You will need to install the 10 mm steering stops or use 5 mm spacers to compensate if you stick with the 6 mm steering stops.

dutchcrunch

hello,

dont want to offend anyone but i noticed that according to stamp of a 964 6 inch wheel the stamp at valve stem says 52. so i believe that there is a mistake somewhere. the book states 55. i always wondered about putting 8 inch wheels all around and having the option to rotate tires to get max wear out of them. seems possible. i am curious to all the respones this will bring.

pete000

According to this cool offset calculator.

The clearance from stut housing to the inside of the wheel will be 22mm LESS
The outside edge of the wheel will EXTEND an extra 28mm

Check it out at: http://www.mindspring.com/~toy4two/offset.html

BGLeduc

I'll be damned...

Both my fronts and rears do say 52. The book does list a Forged Aluminum 6x16 with a "944" part number and a 52mm offset. Don't know what those look lke.

Not to worry...surely Adrian is on case.

BGL

BGLeduc

Bogus math there, Brian (and to think, my Dad was a math teacher!). That should teach me to ASSume.

Took a look at Pete's link as well as the Tire Rack site. The extra width is evenly distributed between the inner and outer wheel sections.

So, spacers may be required, since I have not yet done the steering stops.

And thats a pretty neat site there, Pete. Definetly will be book marking that one!

BGL

Madridcab

In the "wringing out the Carrera 4" articles, I believe from memory they used 16" D90´s with 8 inches front (the std rear wheel) and 9 inches rear (from 944T/928), so it should be tried and tested

vove

It should, Im running 17X8 up front but I do get a slight rub if turning all the way.

BGLeduc

Yeah, my road wheels are MM Cup 1 replicas in 17x7.5, but I don't know the offset, so I was not sure if they would be a reasonable comparison.

BGL

Adrian

Actually the testing done in the USA (article quoted) used the D90s from which were also used on the Carrera 4RS.
7JX16 and 9JX16.
Ciao,
Adrian
964C4

joey bagadonuts

I run an 8" Fikse with 55mm offset up front, Brian. The tires are Michelin Pilot Sport Cups in the 225/45/17 variety. Out back, I've got 9-1/2" rims with 50mm offsets.

There's some rub at full lock but nothing dramatic. My mechanic actually advised against the steering stops--he said I'd be better off with the greater steering range. I still have the stops in case anyone's interested.

For autocross, I think you're definitely on to something. The same size tires & wheels at all four corners should allow you to drive your C2 like a go kart.

BGLeduc

Yup. The thought crossed my mind that I could do a 245 at both ends, not to mention the fact that I could actually rotate the tires front to back between events, so I could replace them all at once, rather than two sets of rears per set of fronts.

I consider the dominant trait of my C2 (with me behind the wheel) is understeer, although its a lot more balanced than a lot of people might think.

But anything to increase front end grip would be beneficial in terms of getting the car to rotate in tight turns. My initial motivation was simply to get a better wheel for the 225 tire I am running now, but if it will fit on a proper wheel, a 245 might be an interesting experiment.

If I have time this weekend (not looking promising, but maybe Sunday), I may bolt the 245 16x8's on the front and take a few laps around the neighborhood

BGL

joey bagadonuts

The 245's up front may be too much tire unless your fenders are rolled and your ride height provides sufficient clearance. Even then, I know some Club Racers who opt for 245/40/17 Hoosiers up front because the taller tires rub too much.

If I wanted to run the same tires front and rear, I'd opt for the 225/45/17. While the contact patch may be a little smaller, there's also less sidewall flex. The smaller rears will also help with rotation and you already know they fit. My guess is that you'll get some fender rub on the outside of your tires under hard cornering. Also, keep in mind that the unrolled fenders have a sharp edge which may cut into the tire's shoulders under hard cornering.
Good luck. I'm very interested to see what you find out.

P.S. Sorry, I just recalled that you're experimenting with 16's but I think the sidewal height and clearance issues may be similar.

BGLeduc

Finally had some time to swap my fronts for the 245/50-16's, which are my normal rear competition tires/wheels (factory 16x8 design 90's).

For background, the car is a US spec '90 C2, running Bilstiens HDs and H&R progressives. Ride height in front is about Euro RS (25.5" from the ground to the fender lip).

Based on bolting them on, and taking a few laps around the neighborhood (including various speedbumps, low speed swerving, and some full lock donuts) I would say that they may work. Maybe. I hope....

I don't think I will give them a 100% blessing until I run a few hot laps, but it looks promising. That said, I really don't see that I can get the suspension moving around enough on the street, thus my reluctance to bless this without some autocross/track laps.

But, here's what I can say.

First off, there does not appear to be any issues with rubbing on the strut or any other section of the suspension. I lack a lift, and thus was unable to really see how much clearance there was from the back of the wheel/tire to the strut, but I could stick a finger tip in there, and there was no evidence of any metal/metal or metal/rubber rubbing. The wheel appears to spin freely.

As for tire rubbing on the inner fender, its pretty much the same as my street 17 Cup One replicas (205 tires on 7.5 wheels). There is inner fender rubbing on the left side when the steering wheel is cranked full left (the inside back of the tire contacts the inner fender), but no rubbing that I can see anywhere on the right side.

Again, my 225 competition tires (on my 16x6 wheels) and my 17" street tires do this as well (no steering stops or spacers have been fitted).

Also, there does appear to be adequate clearance from the top of the tire to the fender lip. I would expect this, as the diameter should be pretty much the same as the factory wheel/tires. I did note that the fender lip, at the top of the arc appears to have been rolled a bit. I know I did not do this, so it may have been a PO or it may leave the factory this way.

Now, the 16x8's do extend out about 1" further than the 16x6's, but they do not extend out beyond the fender lip. Of course, if spacers become a necessity, then that will no longer be true.

So, the next step will be to get a 2nd set of 16x8's. I think I will first mount up the 225's, and give them a go (they still have some life left in them). If that works all right, then when its time for new rubber, a set of four 245's will be ordered.

BGL

joey bagadonuts

Mine is like that as well, so I'd guess it's a Factory job.
Good info on the 245's up front. Thanks for the update.