21 Jul 2021
kjhurleyApologies for the rather lengthy post, but I thought I would put as much detail in as I could, as the issue I have encountered could potentially affect many members (and not necessarily owners of just 991s). My issue concerns tyre tread measurements, which I thought I'd share for information and comment. As it involves 2 OPCs which I know I can't name because of Forum rules, let's call them OPCA and OPCB. Last September, I discovered a slow puncture in one of my rear tyres and contacted OPCA (my nearest) to book the car in to be looked into. Because they had just re-opened following the Covid lockdown, they could not give me a date for this, so I contacted OPCB who were very helpful and fitted me in a few days later. To add insult to injury, I picked up a second puncture to one of my front tyres literally just before I reached the dealership(!). The upshot of all this is that I had to have 4 x brand new correctly N-rated Pirelli P-zeroes fitted at not inconsiderable cost. Since then, the car has done 1,500 miles. I recently visited OPCA to have the PCM software upgrade carried out. As normal, they carried out a vehicle health check at the same time, and to my consternation reported that both rear tyres had a 5.00mm tread depth and were 47% worn. This pushed them into Amber / Advisory status as dictated by Porsche and whilst they did not need changing immediately, they potentially would need doing shortly. The front tyres, although better with a 6.0mm tread depth, were still rated as 31% worn. I immediately went back to query this as the readings just did not sound right for a new set of tyres that had only done 1,500 miles. The OPC double checked the readings for me, and came back to say that they were correct. I then contacted OPCB who had fitted the new set of tyres and they were equally bemused by this. Their After-Sales Manager could not have been more helpful and sent someone round the following day to pick the car up and bring it back to the centre for them to investigate whether there was some sort of problem with the tyres they had fitted back in September. After their investigation of date codes etc., they reported the following tread depths on the rear tyres at their 3 measurement points: 6.1mm / 6.6mm / 7.4mm (passenger side) and 7.6mm / 7.4mm / 6.3mm (driver side). For comparison purposes, they also measured a brand new set of rear Pirelli P-zeroes to the same spec and reported the following tread depths at their 3 measurement points: 7.9mm / 7.6mm / 6.9mm. The upshot of this was for them to say that there was nothing wrong with my tyres and wear was in line with the mileage carried out. They then returned the car the following day. I then went back via the Centre Principal at OPCA to express my dissatisfaction with the inconvenience this had caused me and to get him to investigate the matter further. This resulted in them identifying that they had a problem with the software that generates the health check information in that the control tread depths for Pirelli's had been incorrectly recorded following a software upgrade, and this was the reason for the very high percentage worn reading (i.e. they had been set at 9mm+ instead of the correct control depth of 6/7mm). The rear tyre tread wear percentage therefore should have been shown as 20% and not 47%. I went back again and outlined that whilst this explained the erroneous very high wear percentage, it did not explain the discrepancy between the 3 tread depth readings reported by OPCB and the 5mm tread depth out of OPCA's health check. Their explanation to this, and I quote, was: 'After viewing the video from OPCB, I would comment that their tyre measurements, although accurate, are not in line with our normal measurement practises at Porsche Retail Group. There are 5 depth points across the centre ¾ of the Tyre to consider. OPCB have clearly used the 3 inner most points which will give a similar reading. We at OPCA (and Porsche Retail Group) use the outer most points and the centre point to give a more accurate spread of wear. The risk of using the inner most points is an under inflated tyre will be less easy to identify, along with excess shoulder wear from poor geometry adjustment'. I am not sure whether anyone else has experienced this, but my conclusions are that a) 2 OPCs have a different method of calculating and reporting tyre depths and b) Porsche Retail Group's apparent method can lead to an artificially low reading which could result in customers changing their tyres when there is actually nothing wrong with them. (I still fail to see how doing 1,500 miles on a brand new set of tyres can result in the rear ones going into advisory status, and therefore I am personally more persuaded by OPCB's method (and impressed by their excellent customer service) with the upshot that I am considering changing my servicing to OPCB in future, whilst it is further away). Any of your feedback on this ramble is welcomed! Keith
ralphmusic What I do not understand is that they will sell cars with a minimum of 3mm tread
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