BobbyB

I'm thinking of getting after market wheels (Gemballa Competition) for my 96 993 C4S. The stock wheels are 8/10 x 18. It was suggested to me to go with 8.5/11 x 18.

My question is what if any are the advantages of going with larger wheels?
Are there any disadvantages?

Also which does the C4S have, over steer or under steer? I thought I had it figured then I remember this is an AWD car.

TIA for any information,

Matt Vaughan

Sure, more grip! There's also a disadvantage of a potential weight penalty, unless you go with light aftermarket jobs... The most important aspect will probably be, especially for a 4WD car, to maintain the overall diameter of the tires, front to rear.

Jeff 993TT

Larger front wheels will have more of a tendancy to "tram line" in road grooves.

I agree with Matt about keeping the ratios similar to stock. The rear wheels are slightly smaller than the front, to keep a small amount of power always applied to the front wheels.

If you are trying to dial out understeer, I'd suggest that you look at suspension/sway bars first over upgrading the wheels.

ca993twin

I'm swapping out the wheels on my 993TT to Kinesis 8.5x18 and 10.5x18. With those sizes, I can run the stock size tires or I can "supersize" to a notch or two wider. More tire width generally means more grip. It also looks cool as hell.

With stock suspension setups, Porsches generally understeer right up until you make a mistake, then they'll bite you in the butt.

nota_troll

A friend made an observation to me. Correct me if I'm wrong. Won't larger/wider rear tires accentuate understeer with more grip hence more 'drive' from the rear?

Just curious.

David in LA

Bobby - I have these wheels in this exact size combo on my NB cab. The primary disacvantages with increasing rim width are: a) increased weight; and b) if you are staying with 225/285 size tires then the tires will stretch more - while this helps for handling, you increase the risk of curb rash. If you search under my name there are a few pics posted which show how stretched this tire size will be on these rim sizes.

FYI, b/c of liability issues all cars are set up with understeer incl. recent vintage porsches. Generally, whether you will increase or reduce understeer will be determined by the tire width/size, not the size of the rims. I say generally b/c wider rims will stretch the footprint of a given tire more than a narrow rim (as long as it is not too wide)....so assuming you stay with a 225 front tire, moving up to an 8.5 wide rim can result in a SLIGHT increase in the footprint of the front tires which will reduce understeer....but this may be offset by the increased footprint of your rear tires (assuming you stayed with 285s).

For my car, I did not notice any change in understeer when I changed rims...but then dialed in some oversteer via the rear swaybar. If I were to do it again, I would get a 9" rim and use 235 or 245 size tires in the front, but my car is 2WD so I don't have the circumfrence considerations that you have.

Good luck

David in LA

That's correct - increased grip in rear = more understeer and vice versa for the front. And stiffening up the swaybar in the rear while leaving the front sway bar alone will reduce understeer by reducing grip.

Singh

I went from my stock 17" cups to 18" RS replicas. I think they looked great and made the ride more harsh (M030 suspension).

However, I have gone back to my 17s because on the 18s, the car felt left intimate, less manouverable and very flat footed. It lost its delicacy which is one of the best things about the car.

The 18s were slightly heavier (with tyres) than my 17s. I didn't think a few kgs would make much difference but it did - I guess its all unsprung weight so it makes a big difference. I also found the car tramlined a lot.

I know many guys who have never looked back from 18s but for me, the car drives better with 17s (but looks better with 18s).

adsc4s

Correct, as David confirmed. However, in this case, the fronts are also going wider as well. So the affect on under/oversteer should be minimal. IMHO, 18's are the best combo of looks and performance.

BobbyB

Thanks to everyone for all of the information. It's a lot to digest. Seems the majority feels that the setup 8.5/11's will increase the over-steer just slightly if I keep the same size tires, but not give a real distinct advantage.

Currently I've been offered the 8.5/11 at the same price as the 8/10's. If there is no advantage, I think I will see if I can get the 8/10's for a few less $ and keep a stock setup.

Once again - thank you to everyone.

adsc4s

Bobby, I have 8.5" and 11" HRE's on my C4S. They really fill up the wheel well and as long as your car is lowered, makes the car look really aggressive. No more ugly gap. I do not think the balance of your car will be affected (over/understeer) by going wider BUT you will get increased grip by going wider. Go wider.

David in LA

Bobby -

Not sure about the majority, but I personally think that you should get the 8.5/11s. If you keep the tire size 225/285 then there will be negligible effects on understeer, as I posted above.

I upgraded to this size from 8/10s solid spoke Twists and I think that I'm one of the few here who have firsthand experience with this wheel and more importantly with these rim widths...I think only a few other are running 11" rears (FYI Adscab has used 11" Twist IIs and HREs). The benefit you get with 8.5/11s will be cosmetics (esp if the car is lowered) and the ability to increase your tire size up to 235-245 and 295-305 if you desire (I will qualify myself though in that my car is a 2WD so I can't speak to any 4WD-related issues.)

BTW I believe you can fit the 11.5" Gemballas on a WB 993. My $0.02.

BobbyB

David and Adscab911,

thanks for the additional information - I think I will follow along with your advise and go wider and keep the tires the same size -

David, as you have experience with these wheels in particular - your .02 is worth much more.

Adscab911 - you have the same size w/C4S and have addressed my issues regarding AWD.

thanks again - wider we will go.