944visage

Is anybody out there with a C4S or TT running All Season Tires on OEM Wheels?

I have searched and read on the forum a lot of opinions which are most often enough negative to not change anything from what tire sizes that Porsche specifies and also have been advised by my dealer service manager that Porsche does not specify any All Season Tires for use on a Type 996 C4S or TT but want to see what you experts and those who have actually run All Season Tires on OEM Wheels for the C4S or TT have to say about the subject since really would like to try this out for the winter here in drought ridden California where I might only need them 8 to 10 weekends during ski season if we actually get snow this year!

I have a 2003 C4S (Same wheels As TT) with OEM 18 x 8 Front (225/40-18) and 18 x 11 (295/30-18) Rear Wheels.

I have not lowered the car.

OEM Wheels and Tires: (0.5% OEM Circumferential Difference Front to Rear)

225/40-18 Front (78.82" Circumference)
290/30-18 Rear (78.45" Circumference)

Propsed Option 1: (3% Circumferential Difference Front to Rear)
225/40-18 Front (78.82" Circumference)
285/35-18 Rear (81.21" Circumference)

Option 2: (1.7% Circumferential Difference Front to Rear)
235/40-18 Front (79.8" Circumference)
285/35-18 Rear (81.21" Circumference)

With regard to Tire selection or Option 1 or 2 was either going to go with the Michelin Pilot Sport AS/3 or possibly the Pirelli P Zero Nero (happy with on my Audi S4) that they have on closeout for a great price.

Any thoughts and help would be greatly appreciated!

theclutch

If you want to run the car in the winter, then Tirerack's suggestion is as follows:

18" Recommended Front: 225/40-18
18" Recommended Rear: 265/35-18

The difference between these two is .21 inches. At 65mph, the other is at 65.56

You would then be able to mount the Michelin Pilot Sport AS/3

Dennis C

That is the Porsche recommendation too, but they recommend dropping down to a 10x18 rear wheel. That's what I used for my winter tires on my C4S.

Schnauzer

I have a 2003 C4S and just put my Michelin Pilot Sport AS3 tires on for my winter use. They are 235/40-18 and 285/35-18 on the factory 8" and 11" wide rims. I am very happy with them. I get no codes from the AWD system due to the diameter difference. They do not rub, are much quieter than the PS2s they replaced (worn out) and smoother over road cracks. They seem to grip fine but I have not pushed them in rain or tried them in snow yet. Tire Rack told me they would not be as good as Continental DWS in the snow but rain is more of a question here in Seattle.

The car sits 0.15" higher in the front and 0.45" higher in the rear but this is not noticeable to me. The speedo still reads about 2 mph higher than my GPS. This is closer than before.

I choose the 285 rears over the 265 in the manual so that the width would look more normal. I also did not want to go down to the 10" wheels needed for the 265 tires.

Dennis C

I don't think you would see a code because of a diameter difference that exceeds Porsche's recommendations. It's a mechanical system. You wouldn't find out about an issue until your front differential failed.

theclutch

Yeah that would suck! A friend of mine turned down a 996 Turbo after a PPI revealed "noises" coming from the front diff. Dealer quoted $5600 + labor. I told him to walk away since the previous owner most likely did something screwy on tire sizing. I feel for the poor bastard that doesn't do a PPI on that car and hope serious bad karma falls on that non Porsche dealer who sells it knowing the diff is busted...

Macster

Uh, I hate to burst your bubble but there are no experts here.

All you will get are reports which essentially boil down to I tried X, Y, or Z, and apparently nothing bad happened (so far).

My advice to owners with the C4S (or Turbo) and its AWD system and viscous coupling is to stick with tire/wheel combinations sanctioned by Porsche.

My concern is if you deviate from these and end up with tire/wheel combination that results in more rolling circumference differences between the rear and front wheels/tires than those from sanctioned tire/wheel combinations these differences will over stress the viscous coupling and ruin it.

(Just the other day I came upon a Turbo in for a new front diff/viscous coupling: An incompetent tow truck operator towed the car on two wheels rather than dolly it or order up a flat bed truck and this ruined the front diff/viscous coupling. Cost to replace? $3K.)

In areas where snow is often common all season tires are referred to as no season tires. They do not perform as well as the factory sanctioned summer tires in dry/warm conditions and they do not perform as well as the factory sanctioned snow tires in cold/snow/icy conditions.

Get a set of proper and properly sized snow tires -- ideally with their own set of wheels -- fitted and avoid any worry about any damage to the viscous coupling and be assured the car is fitted with the best tires for the conditions in which you will be driving the car.

In this case you will be foliowing the recommendations of the only expert regarding proper tires for these cars: Porsche.

Gretch

Who is it who contemplates running a TT in snow?????????!!!!!!!!

Geebus, mang!

944visage

Thanks for the info everyone?

I punted for now and put on new rear Michelin PS2's and will have to take the C4S to Tahoe during fair weather weekends only I suppose until I either:

a) buy a dedicated set of wheels and tires which requires the 18 x 10 rear wheel to properly fit the 265/35/18

oir

b) go with Schnauzer's approach since he went with my origiinal postings Option 2 sizes with the AS3 just like I was leaning towards. Hey Schnauzer, if you see this would be very interested in a follow up report once you try them out in some light to moderate snow?

I just don't see how the Option 2 (Schnauzer sizes) that provides a 1.7% circumferential difference of front to rear from my original calculation can put the Diff at risk, particularly when the rear tire wears faster so is going to actually get closer to the front with wear. If you look at the OEM size circumferential difference of 0.5% that actually increases with rear wear then would think the tolerance is close enough but am certainly not a Porsche engineer. I should have measured my rear tires when I took them off last week since would have been curious to see what the difference is with the OEM setup with worn rears and 50% plus tread on fronts.

ChicagoSpeed996

I bit the bullet and went to tire rack and got the Porsche recommended sized winter tires and wheels. $1800 for the set, taxed, mounted and shipped.