Tires too small?
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Rennlist Member
Joined: Oct 2010
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Tires too small?
OK, I searched. I did.
And it's kind of an odd question so maybe thats why I didn't find anything.
Had a PPI done on the C4S I just bought and the wrench said the car had 285s on the rear and its supposed to have 295s. I'm kind of a tire freak so I don't like them being the wrong size, but whats more concerning to me is the wrench said it's not good for the trans'/diffs with different sidewall roll loads. I'm not tracking and I'm not quite ready to see if I can out run the local law enforcement yet, so what level of concern should I have until I get around to swapping them out. They're practically brand new P Zeros that were put on by the Porsche dealership (which I don't like that a dealership put on the wrong size tire). Anyway, just looking for insight, tires are a lot less expensive than trans work.
And it's kind of an odd question so maybe thats why I didn't find anything.
Had a PPI done on the C4S I just bought and the wrench said the car had 285s on the rear and its supposed to have 295s. I'm kind of a tire freak so I don't like them being the wrong size, but whats more concerning to me is the wrench said it's not good for the trans'/diffs with different sidewall roll loads. I'm not tracking and I'm not quite ready to see if I can out run the local law enforcement yet, so what level of concern should I have until I get around to swapping them out. They're practically brand new P Zeros that were put on by the Porsche dealership (which I don't like that a dealership put on the wrong size tire). Anyway, just looking for insight, tires are a lot less expensive than trans work.
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Joined: Dec 2011
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From: Gig Harbor, WA
You have pretty much nothing to worry about. You're not going to hurt the front diff running a 285 as opposed to a 295. Worst case scenario, the visous coupling might get a little warmer than usual, but for regular everyday driving, it won't be enough extra heat to wear anything out prematurely.
The difference in diameter between a 285/30 and a 295/30 is less than 1%. Assuming you have 225/40s in the front, that's a 1.4% diameter difference overall (with the 295s, the difference is about .5%).
When staggering tire sizes with AWD cars, the generally accepted rule of thumb is the diameter difference from front to rear should be under 3% (Audi factory manuals recommend under 5%).
The difference in diameter between a 285/30 and a 295/30 is less than 1%. Assuming you have 225/40s in the front, that's a 1.4% diameter difference overall (with the 295s, the difference is about .5%).
When staggering tire sizes with AWD cars, the generally accepted rule of thumb is the diameter difference from front to rear should be under 3% (Audi factory manuals recommend under 5%).
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Joined: May 2008
Posts: 5,544
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From: Northern NJ
Oh Man, Maurice you should be on Stage!! You would have them rolling in the aisles..
I'm sure that they would be happy to sell you the right ones after you buy a pre-owned car from them.
Here is another "Dealers are the least expensive place to service your Porsche."
I'm sure that they would be happy to sell you the right ones after you buy a pre-owned car from them.
Here is another "Dealers are the least expensive place to service your Porsche."
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Joe Kucinski
Race Director
Joined: Sep 2006
Posts: 19,031
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From: Bentonville, AR
I do not have the info in front of me for the C4S but my Turbo with AWD lists tire sizes as: 225/40 ZR 18 on the fronts; 295/30 ZR 18 on the rears.
My understanding is and I think somewhere in my references... yes, here's the Warning:
Danger of injury or damage to properly as a result of modified handling behavior if tires are used which do not correspond to Porsche-specific requirements.
Unless the owners manual for your car, or a TSB allows for the tire size combination your car has the car has teh wrong sized tires.
While it is not likely the car will dart into a ditch I would be concerned about wear/tear to the viscous coupling and other AWD components. Furthermore I'd hate to have the PSM or ABS compromised due to incorrect/unsupported tire sizes being fitted.
Unless the dealer can show you something official that oks the tire sizes on the car I'd insist the right tire sizes be fitted at the dealer's expense.
Sincerely,
Macster.
My understanding is and I think somewhere in my references... yes, here's the Warning:
Danger of injury or damage to properly as a result of modified handling behavior if tires are used which do not correspond to Porsche-specific requirements.
Unless the owners manual for your car, or a TSB allows for the tire size combination your car has the car has teh wrong sized tires.
While it is not likely the car will dart into a ditch I would be concerned about wear/tear to the viscous coupling and other AWD components. Furthermore I'd hate to have the PSM or ABS compromised due to incorrect/unsupported tire sizes being fitted.
Unless the dealer can show you something official that oks the tire sizes on the car I'd insist the right tire sizes be fitted at the dealer's expense.
Sincerely,
Macster.
Pro
Joined: Jan 2008
Posts: 720
Likes: 10
From: On the snow and Putnam County, NY
This is from a 2003 owner's manual (p.246 - technical data) for 911 Carrera, Carrera and Carrera 4S
They don't seem to specify which is the 4S, although mine is the last with 295's
Hope this helps a bit.
Eric
Summer tires
front 205/50 ZR 17 7 J x 17 H2 50 mm 57.7 in./1465 mm
rear 255/40 ZR 17 9 J x 17 H2 55 mm 59.1 in./1500 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
52 mm 57.3 in./1461 mm
rear 285/30 ZR 18 10 J x 18 H2 65 mm 58.3 in./1480 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
rear 295/30 ZR 18 11 J x 18 H2 63 mm 58.4 in./1484 mm
They don't seem to specify which is the 4S, although mine is the last with 295's
Hope this helps a bit.
Eric
Summer tires
front 205/50 ZR 17 7 J x 17 H2 50 mm 57.7 in./1465 mm
rear 255/40 ZR 17 9 J x 17 H2 55 mm 59.1 in./1500 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
52 mm 57.3 in./1461 mm
rear 285/30 ZR 18 10 J x 18 H2 65 mm 58.3 in./1480 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
rear 295/30 ZR 18 11 J x 18 H2 63 mm 58.4 in./1484 mm
Racer
Joined: Apr 2011
Posts: 367
Likes: 2
From: central massachusetts
This is from a 2003 owner's manual (p.246 - technical data) for 911 Carrera, Carrera and Carrera 4S
They don't seem to specify which is the 4S, although mine is the last with 295's
Hope this helps a bit.
Eric
Summer tires
front 205/50 ZR 17 7 J x 17 H2 50 mm 57.7 in./1465 mm
rear 255/40 ZR 17 9 J x 17 H2 55 mm 59.1 in./1500 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
52 mm 57.3 in./1461 mm
rear 285/30 ZR 18 10 J x 18 H2 65 mm 58.3 in./1480 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
rear 295/30 ZR 18 11 J x 18 H2 63 mm 58.4 in./1484 mm
They don't seem to specify which is the 4S, although mine is the last with 295's
Hope this helps a bit.
Eric
Summer tires
front 205/50 ZR 17 7 J x 17 H2 50 mm 57.7 in./1465 mm
rear 255/40 ZR 17 9 J x 17 H2 55 mm 59.1 in./1500 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
52 mm 57.3 in./1461 mm
rear 285/30 ZR 18 10 J x 18 H2 65 mm 58.3 in./1480 mm
or
front 225/40 ZR 18 8 J x 18 H2 50 mm 57.7 in./1465 mm
rear 295/30 ZR 18 11 J x 18 H2 63 mm 58.4 in./1484 mm
front 225/40 ZR 18 8 J x 18 H2 50 mm 5797 in./1472 mm
rear 295/30 ZR 18 11 J x 18 H2 45 mm 60.2 in./1528 mm
or
rear 295/30 ZR 18 11 J x 18 H2 63 mm (only with17 mm spacer ring)
60.1 in./1526 mm
Thread Starter
Rennlist Member
Joined: Oct 2010
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OK, so I'm getting the impression that I'm "ok" for now, but will be better off swapping out to 295s.
I have no idea what wheels I have, they're stock as far as I know. Did the C4S come with different options?
I have no idea what wheels I have, they're stock as far as I know. Did the C4S come with different options?