996 C4S tire size clarification

[JeanJohn]

I am nearing end of life on my 2003 C4S' Contis, 225/40 front, 295/30 rear. The Porsche North America web site, Michelin web site, my owners manual and several tire sites show 285/30 as the appropriate match for the 225/40 fronts. Tire Rack says that the rears should be 295/30 because "an all wheel drive car needs tires that are the same height front and rear and that only the 295/30's meet this requirement". Is Tire Rack right? The local Porsche dealer does not have an answer. I called Michelin but they were closed for the week for the Holidays. Porsche NA does not have a phone number that I can find.

The question has significance because I am considering Michelin Pilot Sport A/S Plus' for the C4S and the largest size available is 285/30. The reason I like the A/S is that a set of high performance (Michelin, Dunlop, Conti, Pirelli, I tried them all) tires for my 1982 SC lasted about a year until I installed the Michelin A/S and I have had these on for three plus years now with no noticeable wear. I don't track either of these cars, and rarely top 85 MPH in normal beltway and interstate driving in Northern Virginia. The A/S’ seem to have more than adequate handling for the way I drive, are cheaper than the PS2’s I would buy otherwise, offer improved wet weather and cold traction, and hopefully will last more than a year on the C4.

Any suggestions/opinions will be carefully weighed.

[Loren]

:welcome:

C4S is a widebody Carrera (not to be confused with the narrow body C4) and the factory default sizes are 225/40 x 18 front and 295/30 x 18 rears.

[JeanJohn]

:welcome:

C4S is a widebody Carrera (not to be confused with the narrow body C4) and the factory default sizes are 225/40 x 18 front and 295/30 x 18 rears.

I undertstand and your response agrees with the Tire Rack claim. However, as noted, the owners manual shows 285/30 as does the Porsche North America Web site and the Micheline web site when you select C4S as the type. I'm trying to understand where the two recommendations diverge and whether Tire Rack's assertion that 295/30s are required to keep the tires the same diameter for all wheel drive is a true statement and if not adhered to will eventually affect some form of malfunction.

[Loren]

My information comes from the Porsche TSB 18/04 4440 Summer Wheels, Tires, and Spacers (C4S) -- dated May 29, 2008.

Ask your dealer for it or become a Contributing Member here and read it for yourself.

[jgriffin56]

I too have a C4S CAB 04 and the Owners Manual on page 249 for 911 Carrera 4S states for Summer tires Front 225x40 ZR 18 and Rear 295x30 ZR 18. I have the OM right in front and me and I would go with that as Gospel! Make sure that you have the stock rims with are 8"front and 11" rears, or that could change everything.

[TTJunkie]

You can actually run with a wide variety of tires, provided the front and rear tires have the same outer diameter.

If you're interested in Michelins, go to www.michelinman.com and select the rear tire you most prefer. Then go to the spec detail and note the height and revolutions per mile, then find a corresponding front tire with a height +/- .2" or 10 revolutions per mile.

I run 335/30/18 rear and 245/40/18 front Michelin Pilot Sport PS2's on my C4S. It's a little more than you require, and a lot more than stock wheels will allow, but it's well within tolerances for the differential/PSM/ABS systems on the 996 C4S.

[JeanJohn]

I too have a C4S CAB 04 and the Owners Manual on page 249 for 911 Carrera 4S states for Summer tires Front 225x40 ZR 18 and Rear 295x30 ZR 18. I have the OM right in front and me and I would go with that as Gospel! Make sure that you have the stock rims with are 8"front and 11" rears, or that could change everything.

Are the 03 C4S and 04 C4S spec'd with the same tire sizes. Seems like they should be but at the same time Porsche does uplift selected components year over year.

[JeanJohn]

You can actually run with a wide variety of tires, provided the front and rear tires have the same outer diameter.

If you're interested in Michelins, go to www.michelinman.com and select the rear tire you most prefer. Then go to the spec detail and note the height and revolutions per mile, then find a corresponding front tire with a height +/- .2" or 10 revolutions per mile.

I run 335/30/18 rear and 245/40/18 front Michelin Pilot Sport PS2's on my C4S. It's a little more than you require, and a lot more than stock wheels will allow, but it's well within tolerances for the differential/PSM/ABS systems on the 996 C4S.

Great information that I would never have thought to look for (or how), especially since Michelin appears to be showing the incorrect sizes for the 03 C4S. Thanks.

[su20]

This is good info. I am running Pilot Sports on my C4S right now, and the rears are wearing extremely quickly. My driving style is similar to yours, so I may try this option next.

I just checked the Michelin site, and Pilot Sport A/S Plus in the following configuration is withing the 2% tolerance:

(sorry I can't get this formatted into columns... tire size, then Michelin part number, then diameter, then revolutions/mile. Difference is 1.3%.)

Mich part dia rev/m

225/40ZR18/XL 21977 25.08 829

285/30ZR18/XL 20061 24.76 840

difference -1.3% 1.3%

Edited January 1, 2009 by su20

[JeanJohn]

This is good info. I am running Pilot Sports on my C4S right now, and the rears are wearing extremely quickly. My driving style is similar to yours, so I may try this option next.

I just checked the Michelin site, and Pilot Sport A/S Plus in the following configuration is withing the 2% tolerance:

(sorry I can't get this formatted into columns... tire size, then Michelin part number, then diameter, then revolutions/mile. Difference is 1.3%.)

Mich part dia rev/m

225/40ZR18/XL 21977 25.08 829

285/30ZR18/XL 20061 24.76 840

difference -1.3% 1.3%

Thanks. Great information. Seems like the A/S Plus' would be within specs, provide optimum performance for the type of weather we get here in the mid Atlantic region, and offer dramatically better longevity while still enabling "reasonably" spirited driving. Not to mention they are less expensive than the PS2.

One thing I did notice when I went to the A/S on my 911/SC a few years back is they seemed narrower than the same profile performance tire. So, I'm going to have the dealer order both the A/S and PS2 and will compare to ensure there is not an objectionalbe difference in perceived width at the C4 required size.

[JeanJohn]

This is good info. I am running Pilot Sports on my C4S right now, and the rears are wearing extremely quickly. My driving style is similar to yours, so I may try this option next.

I just checked the Michelin site, and Pilot Sport A/S Plus in the following configuration is withing the 2% tolerance:

(sorry I can't get this formatted into columns... tire size, then Michelin part number, then diameter, then revolutions/mile. Difference is 1.3%.)

Mich part dia rev/m

225/40ZR18/XL 21977 25.08 829

285/30ZR18/XL 20061 24.76 840

difference -1.3% 1.3%

Thanks. Great information. Seems like the A/S Plus' would be within specs, provide optimum performance for the type of weather we get here in the mid Atlantic region, and offer dramatically better longevity while still enabling "reasonably" spirited driving. Not to mention they are less expensive than the PS2.

One thing I did notice when I went to the A/S on my 911/SC a few years back is they seemed narrower than the same profile performance tire. So, I'm going to have the dealer order both the A/S and PS2 and will compare to ensure there is not an objectionalbe difference in perceived width at the C4 required size.

Additional gotch - Michelin tech support confirms as their web site shows that that OEM rear tire for the 2003 C4S is 285/30 even though some other experst say 295/30 and my vehicle has 295/30s mounted.

But, the PS AS Plus 285/30 mounts on 9 1/2" to 10 1/2" wheels while a 295/30 mounts 10" to 11" wheels. So my existing 295/30s could be mounted on 10 1/2" or 11" wheels and now I have to determine which one it is.

Can that be done without dismounting tire and measuring?