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Update---PZero tread depth on a 981


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Pedro,

When tire tread depth is measured on a Pirelli Pzero 265/35 ZR20 which has 4 circumferential grooves, is the outside groove which has no tread wear indicator considered to be part of the measurement? Said another way-----Do you only consider the 3 grooves with wear indicators and if the wear on any of those 3 is under 4mm (the CPO standard), does the tire need to be replaced?
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Blackbird
Pedro,

When tire tread depth is measured on a Pirelli Pzero 265/35 ZR20 which has 4 circumferential grooves, is the outside groove which has no tread wear indicator considered to be part of the measurement? Said another way-----Do you only consider the 3 grooves with wear indicators and if the wear on any of those 3 is under 4mm (the CPO standard), does the tire need to be replaced?

the only time tire replacement under CPO came up was when I was buying a used CPO Turbo. The tires were replaced but not because of wear but because of age. The car was a 2003 and I was buying the in 2009 and the tires were 6+ years old. (They only had 10K miles on them and were nearly new otherwise.)

A tire is considered worn out if any tire grooves are to the wear bars. Because generally these cars tend to wear the center of the rear tires out before the edges often the outside edges of the tires look "ok" while the centers clearly are not ok.

If you are looking at a car to buy and the tires have 4mm of tread left my advice would be to push for either new tires or some adjustment on the price. The tires will be at the wear bars shortly. If any wear bars have been reached consder the tire worn out. If the tire on the other side has not quite reached its wear bars it will have to be replaced too. The max. allowable difference between two tires on the same axle is 30% difference in tread depth.

If the tires -- especially the rear tires -- have wear concentrated at the inner edges (or less common but just in case, out edges) in my experience that's a sign of a "bad" alignment (rear toe is off). So with new tires a proper alignment should be included.
The issue is that their are no wear indicators in the outer groove and the tread depth is < 4mm (CPO standard). The other 3 grooves--2 center and 1 inner have tread depth > 4mm and have wear indicators. The Dealer is saying the outer groove cannot be used to measure tread depth because it has no wear indicator, therefore the tire cannot be replaced.
Rear tires wore even, except the outer groove--on both rear tires; seemed odd since I had a lot of negative rear camber on the alignment which should have put the wear on the inside portion of the tire.
I went up to the dealer and measured the grove depth on a new car's equipped with PZero tires with a tire gauge. The outside groves did have less depth than the other three when brand new.
If i understand the purpose of your question, are you looking to buy a CPO ( or already have) and make sure the tires are good enough to pass that CPO measurement?
I have purchased a 2016 CPO 981 and measured the outer groove on the rear tires and it was <4mm. I questioned it and the dealer said you cannot measure the outer groove because it has no wear indicators.I have requested to see the CPO policy that excludes any groove w/o wear indicators from measurement.
Here's a pic from Porsche's site showing a "tech" measuring the tread depth and he's at the outside groove. (Click on the plus sign at the left rear tire and it takes you to the picture I mention.)

[www.porsche.com]

Below is a link to the CPO checklist and in the section about tires and if the tread depath is less 4mm the tire must be replaced. Doesn't say anything about which grooves to measure or avoid. Thus my interpretation would be any groove with less than 4mm of tread depth would require the tire be replaced to agree with the CPO checklist.

[www.nadaguides.com]
Thanks Marc---I have same interpretation as you--Will find out tomorrow what dealer position is.
Update--Dealer checked with PCNA and the outer groove w/o a wear indicator does qualify for a tread depth measurement.
The tires failed the CPO <4mm standard and will be replaced w/o a charge.
Thanks for your help Marc.
Remember that new tires are kind of "greasy" and it can take a hundred miles or so of use to work the greasiness out of the tires. This is approx. a couple of days of work commute for me at 60 miles a day.
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