7s and 9s on Carerras

[old_skul]

It's almost a done deal with my buddy Rattlsnak from here on the forum. I'll probably pick up his 7 and 9 inch 17" Mille Miglia Cup wheels.

My question for the forum today: what are some of the wear and maintenance considerations I'll need to think about when running these wheels? Aside from sizing the tires so that they don't rub my fenders, will I have to modify anything else to make the car driveable and reliable?

Any of you who run this type of setup please chime in with your experiences, warnings, and tire sizes too, if you don't mind.

[Bill Verburg]

225/45x17 fronts(~25" tall) and 255/40x17 rear(~25.1"tall) should fit well with minimal mods to fender lips and minimal effect on gearing or speedometer( they are just slightly taller than the stock 16" sizes). Wider can be fitted w/ increasing work need for each additional increment of width 235/45 or 245/40 in the front and 265/40 or 275/40 in the back. The extra work is only worth it for a race car. On a street car its just extra work. Unfortunately there are no appropriate 35 series tires available.

[Eric Mckenna]

Mark,
They are very much a daily driver set up.. I had them on my 78SC.. they make the car handle a better IMO..
you will have to either roll the fender or just gring the damn thing off as I did. NO MORE issues! hahah! very easy..
If you're down at Carstons sometime you can llok at mine and see what was done to the fender lip's.. YOU"LL LOVE THE NEW LOOK AND SET UP... they look kick ass and make the car feel better, a bit more bumps will be be noticed as well due to the lower profile tires.. but that just menas you can throw her into a corner harder and she will feel more solid!
Eric

[widebody911]

The wheels should pretty much bolt right up. If you're migrating from 16" Fuchs, and especially 15" Fuchs, you'll really see less acceleration, and your braking distances will increase. These wheels are heavier than Fuchs by a lot, and the larger overall diameter changes the gearing quite a bit. Your speedo will be off as well - it will read a little optimistically after the change.

[Bill Verburg]

Thom, thats why I recommended the 255/40. They are less than 1% off what a 225/50x16 will give in terms of gearing and speedo.

[Chuck Moreland]

I had a set of those wheels, and had to send them back.

The front are 7.5 inch wide. I was running 205/50s and they interfered big time with the fenders, even with lip rolling.

I know a lot of people run these wheels without issue, but I couldn't.

I opted for factory Cup IIs with spacers. Much lighter too.

[Bill Verburg]

The front tire issue is very puzzling. Some folks have reported no go w/ even 205/55x16 on stock 7" Fuchs, while others(me) have run that size and larger w/o any major issues. I am equally amazed by the people that manage 245/40 a size that would never fit on my fronts.

Obviously wheel o/s, width and diameter and tire size or rather variance from nominal are issues. But it is also obvious that there exists a fairly wide range of chassis variance as well.

[cowtown]

I run these Mille Miglia wheels on my '88, but believe the fronts are 7.5x17, not 7x17. Rears are 9x17.

I rolled the front lips up, and run 215s with no problem. Can't us my bra anymore, though, because the tires want to eat the clips that go under the fenders.

I have used 245s and 255s in the rear with no problems. With this setup, there is understeer, and I have no incentive to go any bigger in the rear.

Thom is correct in saying you will notice a drop in acceleration due to weight, but I must disagree about increasing brake distances. I can still lock them up from any speed, and this can only mean I'm at the limit of adhesion. The weight of the wheels is not an issue in this state, as far as I know.

Also, your speedo will read too low, not too high, if you have a wheel/tire combination that is larger-diameter than stock. But with some careful tire selection you can stay close to stock diameters.

[Jack Olsen]

I think it's different with each car. I went from 225's to 245's in front on 7's for the last day of my previous car's life. I had all sorts of contact issues with the leading edge of the fender opening where it meets the bumper. A real PITA. By mid-day, I was a little frustrated that I was going to need to do some repair work on the front bumper.

Then I fixed the front bumper permanently, with a really big piece of concrete. Now, I'm going to have bigger fenders and wider tires.

Mark, if you're paying more than $400/wheel, you might want to consider 2-piece Fuchs. Light. No spacers. Classic look.

[speeder]

Bill and Jack hit it on the head, chassis variance can be very significant on stock 911s. Basically, the front suspension is not symetrical on some of the cars, most rubbing issues occur on one side only. (Can't remember which side).

When I worked at dealer in '86 or '87, we delivered a new 911 coupe to a guy with 7s/8s on it, it had a clearance issue on one side in front. A tire dealer pointed out to the guy that one side had a wider track than the other. (In relation to the car's body/fender). The guy raised holy hell, Porsche bought the car back from him or gave him another one, told us that "this is normal, nothing really wrong here", we put stock wheels on it and sold it all over again. If he had not put 7/8s on it, he would never have noticed it in a hundred years.

[Bill Verburg]

My 235/45x17 on 8s had the same issues at the same place Jack did. The front bumper/fender joint flange. I ground the flange down until there was no more interference,

[expat]

Bill & others - what about 9.5" x 17 wheels on the rear. Do you think these would fit? I've been offered a set REAL cheap but can't get my car to the guy for a while so I can't check it out. Do you think there's a chance they'll fit, or no way?

I've taken note of your advice about tyre size.

Thanks Mark

[old_skul]

Jack, I'm really hoping that putting these wheels on my car doesn't make me want to modify my bumper the way yours is. :\

Cowtown, are the wheels *that* much more heavy? I originally got my 16" Fuchs for that very reason.

[JeremyD]

will 16 x 7 and 16 x 9 Fuchs fit on a stock carerra? or do you have to go with a 16 x 8's for the rear?

I have a set of 17 x 7 and 17 x 9's OZ racing wheels - but I think they might be too much for my car (87 Cab) and I really don't want huge honking spacers on them.

[old_skul]

I have personally seen Fuchs 7s and 9s on a Carrera body with no problems. I have no idea what spacers were used, but it can be done.

I have the replica Cup1 MilleMiglia wheels.

7,5x17 & 9x17 with 215/45 & 245/40. No problems at all until I had the car lowered. That caused rubbing at the left rear tire.

Negative camber solved the problem. I haven't had the fenders rolled.

[Wil Ferch]

Guys:
A slightly different twist on this...
I have a real issue when people say "the body is really variable ...due to the hand-built nature, blah, blah.."
Porsche bodies are some of the most tightly controlled and repeatable in the business. The *real* variable is the tire itself....square shouldered, round shouldered, various sizes between manufacturers and types ( some 225's are equally wide as 245's). Now...this doesn't relieve Porsche of ( say) having produced a car that isn't symmetrical...but this lack of symmetry is likely the same for all cars. If ( say) the driver's side front is a typical problem point...then it would likely be that corner for other cars, too...depending on the tires chosen. I'd like to suggest that whenever anyone one of us publishes data on fittment ( those that work and those that don't)...that we include information on not just tire size, but tire brand name and type, as well as wheel offset if known.
---Wil Ferch

[old_skul]

Good points, Wil. I'd like to know what brands and sizes of tires people run with the various rims and what kinds of problems they had. It would make a whole freakin' website, I'm sure, but that's good info. Sounds like Technical Article fodder to me.

I did a little homework on the weights, and I don't think I'll see even a perceptible difference in acceleration. Check out these wheel weights, garnered from a couple of wheel weight databases on the 'net:

Forged Fuchs, 6s and 7s: 17lb and 18lb, total 70lb for all four wheels.

Forged Fuchs, 7s and 9s: 18lb and 20lb, total 76lb for all four wheels.

Cast MM Cup1s, 7.5s and 9s: 25lb and 28lb, total 106lb for all four wheels.

That leaves me with a delta of only 30lb between the Fuchs solution and the Cup1s. And 36lb more than what I'm running now.

There will be a small difference in tire weight too, but let's call it 10lb overall. So, a 46lb increase in weight. I'm going to be jettisoning my A/C unit next week - and I understand that's like 200lb - so I'm hoping for basically the same performance.

If there's anyone running 7.5s and 9s on a Carrera/SC body, let me know what brand and sizes of tires you're running.

[Wil Ferch]

Old_Skul:
Remember , however, that static weight on a car ( like the A/C system)...yields different results than does the weight of wheels. I think others have already mentioned that unsprung vs sprung weight is a factor...but so is the rotating mass of the wheel trying to be accelerated by the car's engine ( or decelerated by the car's brakes). I would think this rotationbal "inertia" has a component effect all by itself...beyond the weight increase it represents from a "static" standpoint.
OTOH...as correct as this may be from a purely academic standpoint, I wonder how much impact it really has in a real world situation....there, you have a point on questioning the relevance of all this.
---Wil Ferch

[ChrisBennet]

Yeah, what Wil said. Heavy wheels get you 3 ways:
- Increased weight of car
- Unsprung weight making it harder for suspension to react.
- Increased rotational inertial. Those heavy wheels really act like big flywheels. Even if a 17" wheel weighed the same as a 16", (I think) the 17" would have more of its weight concentrated at the perimeter - the worst place from a rotational inertia standpoint. Sport Compact Car showed how heavier wheels effected dyno results on an inertia type rear wheel dyno.
-Chris