Rear tyre terminal puncture - replace the pair? - Page 1 - 911/Carrera GT - PistonHeads UK

On the weekend I got a terminal puncture thanks to a discarded stanley blade on the road... The rear tyres had 5mm of tread. If the new tyre has 8mm of tread does it cause an issue (e.g. for the diff) if one rear tyre has 5mm and the other 8mm? Or is it necessary to replace the rear pair together?

braddo said: On the weekend I got a terminal puncture thanks to a discarded stanley blade on the road... The rear tyres had 5mm of tread. If the new tyre has 8mm of tread does it cause an issue (e.g. for the diff) if one rear tyre has 5mm and the other 8mm? Or is it necessary to replace the rear pair together? I dont think 3mm will make a huge difference, the make and week of manufacture would be more of a concern. As a side note, if you dont replace the pair now then you will have to replace the other side sooner so you will be in the same position 6000 miles down the road. If it was me, I would replace the pair on the axle and then put the one with 5mm left on ebay

Thanks, and I would agree except that the current tyres are P Zero Rossos. Not sure if I want to extend the time that they are on the car by buying a new rear pair! So I guess alternatives would be: - if the tread depth difference isn't an issue, buy a new Rosso and get rid when the other side needs replacing - try to source a part worn replacement Rosso - buy a new pair of different tyres (e.g. PS2s or Supersports) and live with a front/rear difference for a while - replace all 4 tyres now....

braddo said: - try to source a part worn replacement Rosso I may be able to help you there. I also replaced a single rear tyre last year (similar story to your own), but now the other three on the car have worn out; I don't want the Pirellis any more, so will be replacing all 4. I can check the tread depth if you like. Tyre is a 285 / 30 / ZR / 18 - currently in Oxfordshire.

Cheers but I am after a different tyre size - 305/30/19 (N1)

braddo said: - replace all 4 tyres now.... Pirelli aren't even worth burning

braddo said: On the weekend I got a terminal puncture thanks to a discarded stanley blade on the road... The rear tyres had 5mm of tread. If the new tyre has 8mm of tread does it cause an issue (e.g. for the diff) if one rear tyre has 5mm and the other 8mm? Or is it necessary to replace the rear pair together? When replacing one tire Porsche guidelines call for both tires on an axle to be replaced when the old tire is worn more than 30%. Based on the 8mm you gave for a new tire's tread depth and the other tire having 5mm of tread left 30% of 8mm is 2.4mm and 8mm minus 2.4mm is 5.6mm so at 5mm the old tire is 0.6mm undersize according to Porsche's guidelines.

Rockster said: braddo said: On the weekend I got a terminal puncture thanks to a discarded stanley blade on the road... The rear tyres had 5mm of tread. If the new tyre has 8mm of tread does it cause an issue (e.g. for the diff) if one rear tyre has 5mm and the other 8mm? Or is it necessary to replace the rear pair together? When replacing one tire Porsche guidelines call for both tires on an axle to be replaced when the old tire is worn more than 30%. Based on the 8mm you gave for a new tire's tread depth and the other tire having 5mm of tread left 30% of 8mm is 2.4mm and 8mm minus 2.4mm is 5.6mm so at 5mm the old tire is 0.6mm undersize according to Porsche's guidelines. Which is so miniscule it's not worth worrying about.

Rockster said: When replacing one tire Porsche guidelines call for both tires on an axle to be replaced when the old tire is worn more than 30%. Based on the 8mm you gave for a new tire's tread depth and the other tire having 5mm of tread left 30% of 8mm is 2.4mm and 8mm minus 2.4mm is 5.6mm so at 5mm the old tire is 0.6mm undersize according to Porsche's guidelines. You might want to check your maths there. The usable tread is 6.4mm (8-1.6), 30% of which is 1.92mm so once the tread depth is below 6.08mm (shall we call that 6mm?) the tyre is 30% worn.

Rockster said: braddo said: On the weekend I got a terminal puncture thanks to a discarded stanley blade on the road... The rear tyres had 5mm of tread. If the new tyre has 8mm of tread does it cause an issue (e.g. for the diff) if one rear tyre has 5mm and the other 8mm? Or is it necessary to replace the rear pair together? When replacing one tire Porsche guidelines call for both tires on an axle to be replaced when the old tire is worn more than 30%. Based on the 8mm you gave for a new tire's tread depth and the other tire having 5mm of tread left 30% of 8mm is 2.4mm and 8mm minus 2.4mm is 5.6mm so at 5mm the old tire is 0.6mm undersize according to Porsche's guidelines. Posche guidelines are their own idea of what they think is safe, the fact that if people follow them they sell tyres more often has absolutely nothing to do with it..

ttdan said: Posche guidelines are their own idea of what they think is safe, the fact that if people follow them they sell tyres more often has absolutely nothing to do with it.. Very similar to Audi guidlines, if that counts for anything. They replaced all four tyres on mine some years ago (after one tyre suffered uneven wear) at their own cost on the basis that tyre differential shouldn't be more than 3mm. All four because it was 4wd.

Buster73 said: Which is so miniscule it's not worth worrying about. Porsche doesn't give any tolerance. It is 30% difference, not 30% +/- 4%.

thegoose said: You might want to check your maths there. The usable tread is 6.4mm (8-1.6), 30% of which is 1.92mm so once the tread depth is below 6.08mm (shall we call that 6mm?) the tyre is 30% worn. My mistake in not being clear. It is 30% difference in tread depth between the new tire compared to the old one. If there is a 30% difference in tread depths Porsche guideline calls for the old tire to be replaced too.

Mixing tyres across the axle is the main issue, so I'd replace the pair with the brand you want, put the good Pirelli on ebay, it'll sell no problem. If you really aren't comfortable with mixing front to back, get what you want on the front to match the rears and then put the fronts on ebay.