Outside wear on rear tires

[rrspikemarty]

Hi,

The rear tires on my C4S coupe (6-speed manual) are wearing down from the outisde in. I've searched and read a number of posts about inside-out tire wear and wheel alignment, etc, but didn't see anything specific to the outside-in wear pattern. Some of the facts:

- 996 C4S

- PZero Asymmetricos front and rear, with 4,000 miles since new (all mounted at same time) at official Porsche dealer

- Front tires in very nice shape with little wear.

- Car not been tracked

- Considerably sedate driving - I don't throw the car around in curves, nor push much past 80 mph on the freeways, and no rapid 'lay-down-rubber' starts. It is not a daily driver.

- The treads are worn identically on left and right rear tires

- The tread wear is even and smooth all around circumference of the rears - no bald spots, bulges, etc

- The tread wear is smoothly graduated across width of each rear tire, with 6/32 depth on inside and 2/32 on outside edge

- The rears have no cupping

- The steering is tight and straight, with no steering wheel vibration/wobble

- When driving at any speed, there's no unusual noises from the rear that you would expect to hear with out-of balance, or badly aligned wheels

- The car does not pull left or right

- Car is stock everything (no lowering or sport suspension, etc), with no parts damaged or replaced.

- Tire pressure maintained per the owner manual

I think I understand the negative wheel camber requirements for the p-car suspension and the driving it's designed for, and the inside rear tire wear that results, but could it be that my wear pattern is due to camber settings on each wheel that are too far the other way..? I haven't seen or experienced any behaviour you'd associate with wheels out of alignment. Is it possible/advisable to simply get both cambers adjusted, or am I looking at a more extensive alignment service? Or...?

Any recommendations from renntechers on what would be the most cost-effective approach would be much appreciated!

Regards. :D

[Loren]

How many miles on the rear tires?

[White987S]

- PZero Asymmetricos front and rear, with 4,000 miles since new (all mounted at same time) at official Porsche dealer

Loren, I think he is saying the tires (all) have 4,000 miles. Right?

[Loren]

Hmm... missed that.

I would certainly check the alignment - both camber and toe.

[PAULSPEED]

I sure would like to see a picture. I find it hard

to believe unless the tires are mounted wrong. You

should be able to read the words "outside" on

the wheels. If it says inside, then the tires were mounted wrong.

Paul

[Q-Ship986]

Is it also possible that the rear tires were demounted and swapped left/right during recent service? --Brian

Edit: Nevermind, I see with 4000 miles, they would have been mounted incorrectly from the get-go, as Paul wonders above.

Edited September 3, 2008 by Q-Ship986

[RFM]

P zero asimmetrico will have usually a strange wear pattern, if you have to renew them, buy P zero Rosso, if you like to stay with Pirelli or take an other approved brand. Fill up the fuel tank and let check the alignment.

[rrspikemarty]

Thanks everyone for the ideas.. sorry about delay in replying - been out of town for a few days.

Tires were all mounted at same time 4,000 miles ago and not touched since.

Tires have 'Exterieur Outer' on outside-facing walls, as appropriate.

Paul - I've attached some pics, but not sure that the uneven tread wear can be seen very well (the pics are of the passenger side rear; the driver side rear is similar wear)

I'm wondering... if i drive with 5 or 6 bags of sand in the back seat....?

I'll get the camber and toe looked at.

Does anyone have the factory specs for rear camber and toe on the C4S coupe?

[Q-Ship986]

Those look normal. The outside shoulder appears to be solidly tie-barred between the lugs. To measure tread depth, you need to use a gauge in the major circumferential grooves; from your photos, the wear across the tread looks more-or-less even. If anything, the inside looks a bit more worn to me than the outside.

--Brian

Edited September 11, 2008 by Q-Ship986

[PAULSPEED]

The outsides look just like glazing. This is normal and

nothing to worry about. The gage is the only way to measure

when you have so much rubber left on your tires. Show us

some pictures when you get another 6,000 miles

on your tires and then you can look at the rear. In

my world of throwing the car around, these tires look new.

Paul

[rrspikemarty]

Thanks for all your thoughts on this..

....will send more pics in future, but i'm not sure these tires will go another 6,000 miles with the current geometry. :o

[White987S]

Those tires look normal to me too.

[usdmej]

notice how the tire looks darker (less road debris embedded on it) on the outside compared to the inside. that means it's not contacting the road nearly as much as the inside tire is. expect the inner portion to wear away first, which is normal with p-cars unfortunately

[tlh]

Read this a while ago. The tire wear does look pretty normal. However, I had a similar, but much more extreme wear pattern on my 2002 Targa (6 speed). 1st set of rear tires stock Michelin's lasted 12K miles. Replaced with Pirelli's which lasted 6K. (Ouch) Both with normal even wear. Went back to the Michelin's and noted extreme outside wear within 5K miles. Literally NO tread on outer 3", while inner tread barely worn. Almost exclusively freeway driving. Used as a commute car, minimal traffic. Multiple suggestions of tire pressure, etc. from dealers.

Read your issue here and took mine in to get the camber/alignment done. They couldn't get the R wheel to toe in to specs. They then noticed a slight bend and crack in R rear wishbone suspension. Apparently this can happen with towing? Mine had never been towed.

Anyway, now after the alignment 2K on the tires in similar driving conditions with no evidence of wear.

Thanks for all your thoughts on this..

....will send more pics in future, but i'm not sure these tires will go another 6,000 miles with the current geometry. :o

[rrspikemarty]

Read this a while ago. The tire wear does look pretty normal. However, I had a similar, but much more extreme wear pattern on my 2002 Targa (6 speed). 1st set of rear tires stock Michelin's lasted 12K miles. Replaced with Pirelli's which lasted 6K. (Ouch) Both with normal even wear. Went back to the Michelin's and noted extreme outside wear within 5K miles. Literally NO tread on outer 3", while inner tread barely worn. Almost exclusively freeway driving. Used as a commute car, minimal traffic. Multiple suggestions of tire pressure, etc. from dealers.

Read your issue here and took mine in to get the camber/alignment done. They couldn't get the R wheel to toe in to specs. They then noticed a slight bend and crack in R rear wishbone suspension. Apparently this can happen with towing? Mine had never been towed.

Anyway, now after the alignment 2K on the tires in similar driving conditions with no evidence of wear.

Thanks for all your thoughts on this..

....will send more pics in future, but i'm not sure these tires will go another 6,000 miles with the current geometry. :o

tlh,

Interesting to hear of your similar situation. Was the extreme outside wear only on the right rear (related to the wishbone damage?). Was the camber, or toe-in setting the culprit (or both)?

An alignment is in my future.

[violaGT3]

Hi my 2 cents goes like this,

camber wear will normally wear out the inner 1/3rd of the tire 15-20% faster than less aggressive camber settings.

If you are noticing the difference within 2-4,000 miles it sounds like you are toe'd in too much in the rear.

A quick check on that is measure from like points on both rear tires from the front and the rear.

There should be no more than 1/4" difference.

[CJ_Boxster]

Too much toe-in...

[Q-Ship986]

Read this a while ago. The tire wear does look pretty normal. However, I had a similar, but much more extreme wear pattern on my 2002 Targa (6 speed). 1st set of rear tires stock Michelin's lasted 12K miles. Replaced with Pirelli's which lasted 6K. (Ouch) Both with normal even wear. Went back to the Michelin's and noted extreme outside wear within 5K miles. Literally NO tread on outer 3", while inner tread barely worn. Almost exclusively freeway driving. Used as a commute car, minimal traffic. Multiple suggestions of tire pressure, etc. from dealers.

Read your issue here and took mine in to get the camber/alignment done. They couldn't get the R wheel to toe in to specs. They then noticed a slight bend and crack in R rear wishbone suspension. Apparently this can happen with towing? Mine had never been towed.

Anyway, now after the alignment 2K on the tires in similar driving conditions with no evidence of wear.

Thanks for all your thoughts on this..

....will send more pics in future, but i'm not sure these tires will go another 6,000 miles with the current geometry. :o

tlh,

Interesting to hear of your similar situation. Was the extreme outside wear only on the right rear (related to the wishbone damage?). Was the camber, or toe-in setting the culprit (or both)?

An alignment is in my future.

An alignment check is probably not a bad idea, but again, the wear of the tire in your photos not only looks typical, it looks like it is wearing more on the inside portion of the tire. For comparison, I think you may want to look at a new PZero Asimmetrico:

If you get a depth gauge and measure the tread depth in the slots as I have marked with dots on your photo below, you will probably find that the outermost groove (groove 5) is deeper than the innermost groove (groove 1). I think you must be hung up on the difference in appearance of the lateral slots marked by the arrows. The outside shoulder rib has a shallower skid line, which means the lateral slots are not as deep as other slots on other ribs. Note the way the outer shoulder slot is "stepped up" from the groove. The outer skid line tapers to even shallower depth as it approaches the arc point, which is the end of the tread at the outermost edge. This is all typically done to enhance handling performance. Less tread depth and rubber mass increases block stiffness and reduces hysteresis to prevent tread chunking, among other things. Most important on the outside shoulders which endure the most stress/strain under cornering.

Hope that helps.

--Brian

[whip123]

The p zero's are garbage tires. The local porsche dealer in san jose wont even sell them anymore, they only get complaints. get the michelline ps2's. i got 8k miles on my pirellies and 22k on the mich ps2's, both same rating and i know guys that track on mich's and love em. anybody want to make a class action against pirelli for selling such garbage for $370 a pop (jk, waste of time)

Hi,

The rear tires on my C4S coupe (6-speed manual) are wearing down from the outisde in. I've searched and read a number of posts about inside-out tire wear and wheel alignment, etc, but didn't see anything specific to the outside-in wear pattern. Some of the facts:

- 996 C4S

- PZero Asymmetricos front and rear, with 4,000 miles since new (all mounted at same time) at official Porsche dealer

- Front tires in very nice shape with little wear.

- Car not been tracked

- Considerably sedate driving - I don't throw the car around in curves, nor push much past 80 mph on the freeways, and no rapid 'lay-down-rubber' starts. It is not a daily driver.

- The treads are worn identically on left and right rear tires

- The tread wear is even and smooth all around circumference of the rears - no bald spots, bulges, etc

- The tread wear is smoothly graduated across width of each rear tire, with 6/32 depth on inside and 2/32 on outside edge

- The rears have no cupping

- The steering is tight and straight, with no steering wheel vibration/wobble

- When driving at any speed, there's no unusual noises from the rear that you would expect to hear with out-of balance, or badly aligned wheels

- The car does not pull left or right

- Car is stock everything (no lowering or sport suspension, etc), with no parts damaged or replaced.

- Tire pressure maintained per the owner manual

I think I understand the negative wheel camber requirements for the p-car suspension and the driving it's designed for, and the inside rear tire wear that results, but could it be that my wear pattern is due to camber settings on each wheel that are too far the other way..? I haven't seen or experienced any behaviour you'd associate with wheels out of alignment. Is it possible/advisable to simply get both cambers adjusted, or am I looking at a more extensive alignment service? Or...?

Any recommendations from renntechers on what would be the most cost-effective approach would be much appreciated!

Regards. :D