Crystal Cranks

Are the Pirelli Pzeros N rated, the reason I ask is because when I was getting four new P zeros fitted the shop ordered N rated but when they came in two of them where not N rated.
We re ordered and got the N rated ones in and as we had both in the shop when fitting we looked to see if there was any difference in them or was this N rated thing all about nothing.
Turns out there is, there was a big difference in the side walls, the N rated tire had much thicker side walls. (sorry don't want to start a N rated tire argument just my 2c)

Blu RS

What you have are low mileage tires that have apparently gone brittle, particularly judging from the peculiar chunking on the failed sidewall. Ozone can cause embrittlement but your sidewalls don't show the typical aging effects seen by ozone or from excessive exposure to sunlight. The most likely culprit left is heat; i.e., the long term effects of repeated heat cycles from being caught in congested traffic with the left rear in close proximity to the cat converter. Assuming that is indeed the case, the implications are that in the future you will want to replace the left rear tire on a more frequent basis (time versus simple mileage) than before.

tonyc

The tyres are the Pirelli PZero Asimmetrico's which I gather from Streather's book are N2 rated. I remember requesting N rated tyres last time.

Blu RS, can one just replace one tyre? I thought you had to at least replace both rears if not all 4. I know keeping the same type, brand, size etc is important but surely different wear is going to have a negative effect, even after a couple of years.

I'm definitely looking as changing all four this time around.

Blu RS

There are more good reasons to replace both rears at the same time than the one reason not to do so, i.e., cost. You do want both rear tires to have the same circumference, the same hardness (new tires are inherently softer than used tires) and the same construction/size specifications. Those requirements are almost impossible to accommodate when you only swap out one tire. Having said all the foregoing, and depending on the wear on your front tires (i.e., they have less than 10K miles on them) I might not replace the front tires were this my car. Large overall circumference differences between the front tires versus the rear tires can cause your ABS system to be less effective. If the fronts are barely worn, then the circumference difference will be minimal as will the effect on ABS activation. If you find yourself driving at speed in the rain quite a bit then that would be a strong argument for replacing all four tires now. If you seldom drive in the rain and the fronts are barely worn down, then retaining the fronts would still make sense.

tonyc

Thanks for the detailed info, will probably change the whole set as they are around 5 years old. Will post the mechanic's post analysis when I hear from him on Monday.