Hey guys here at D2Autosport we are known for having the best selection of wheels, the latest styles, and a very knowledgeable staff, so we pose the question how can D2AUTOSPORT help you 6speed?

We challenge every one in the market for wheels, tires, aero parts, or suspension needs to contact us. Just tell us what you are looking for, what your budget is, and how soon you need it, we will have something to offer you. Go to D2AUTOSPORT.com and find what you are looking for, give us a call or send a PM with your request and we will handle the rest. Also you may post in the thread below as a request for feedback, thanks.

www.D2AUTOSPORT.com
877-361-0296
Stefan@D2AUTOSPORT.com
Sales@D2AUTOSPORT.com
AIM: D2AUTOSPORTSALES

 

Ok...

i have been trying to get this answer for some time. I have a 2003 Porsche C4S that is obviously all wheel drive and I am looking for new tires to mount on my 8.5 X 19 and 12 X 19 Modular Concept rims. The front rims measure 9.25" and the rears measure 13" outside to outside. It was reccomended that I go with Michellin PS2's which is fine.

Here is my question;

Is the power output equal at all 4 wheels and is handling specifically affected by variation in tire size especiallly on a all wheel drive vehical?

With an all wheel drive car how important is it that the tire dimensions are equal front and rear and can I get a matching set in the Michellin tires?

Ponyboy

 

Did I stump you?

 

Pony, maybe I can help you out.

The widest that we go on that particular application (996 C4S) is 11.5", but if you can fit that 12" in there then more power to ya.

As far as the power output, it varies based on condition, but on the 996 is never equal to all 4 wheels - I believe on the 996 the total drive to the front wheels moves between 5% and 40%. The quick answer is, you could probably put whatever width tires you want as long as the diameters are very close.

A Porsche racing crew chief would be a great person to ask about this, but from what I've heard/read from the important thing when changing mechanical grip levels front/back and trying to keep OEM balance is to increase the amount of grip front and back proportionally - if you add 15% more tire in back, add 15% more tire in front. In all honesty, the viscous AWD system will correct for differences and try to restore the torque split front/back based on which wheels have the most grip, and the worst thing that would happen with mis-matched tire widths (not diameters) is increased wear on the viscous coupling if you slip your rear wheels often (racing, burnouts, etc).

 

I actually went down to Pioneer in San Diego today and spoke with a couple of the mechanics and the numbers I got were a bit different but I think I have a grip on the concept.

Anyway the conversation was interesting for everyone involved and caught everone's attention.

What I was told (and this is subjective at this point) is that the power output to the wheels on a C4S was 90% to the rears and 10% to the fronts. The variation in tire diameters is recommended to be no more than 3%.

So if I went with a 325/30ZR19 on the rears and 225/40ZR19 on the fronts the difference in diameter would be .6" which would fall under the 3% and if anything I would think that it would add to the understeer. Does this sound correct?

Obviously I am getting an education here and playing with my Porsche is a great hobby to be able to have.

Thanks for your response!

Ponyboy

 

The sizes you listed will be 2.2% off, totally within spec. Shouldn't have any problems with the AWD I am curious how well those rears fit, even with a little stretch on there. Be sure to post up some pics!

 

ponyboy, don't confuse diameter with circumference...you are concerned with tire circumference here not diameter

 

i have a 12.5" rear wheel and it fits totally fine

i would love to see you attempt a 325/30/19 though
i dont think it'll work...

 

Chuck,

Makes sense...

Thank you!

 

Steve what size tire are you running? I have 315's on now and I still have plenty of room at the tightest spot which is at the shock head.

I will measure it all up this weekend so I can order the tires.

I have heard that Bridgestones and Continentals have a stiffer sidewall then say P-zeros or Michellins. Would it be a good idea to run a stiffers tires to avoid any rubbing (I am not going to track the car and I drive like a blue hair anyway)?


Ponyboy

 

Hey Pony, I see I've been MIA for a few days and in that time your question has been answered. As for fitment on the 996 the widest we have done is a 12" wide 19" wheel with a 315 tire. The 315 we ran was a PS2 and those run over spec meaning they are thicker then most other brands.
I would think with a pirelli or another brand that runs under spec you can probably get away with that 325 you'd like to run.