endeavour_uk

I just thought I would relate my recent experience with run-flat tyre ownership. My 535d Touring Sport is fitted with Runflats. I do a highish mileage so in a few months shy of two years the original tyres had done over 30000m. So I am not going to be moaning about their longevity. The ride can be a bit harsh, but if you tend to buy cars with sporting pretensions, you would probably not think it unacceptable. It has also been out on the track at Anglesey and really impressed me despite being a very big car to punt round the tight and technical Ty Croes circuit of Fifth Gear fame.

No, my complaints are actually about what runflats are designed for - punctures. The first puncture I got happened at a heady 5mph approaching a dual carriageway slip road - so I don't think I can claim it saved my life. It was a full-on blow-out though complete with loud bang. At first I wasn't sure what it was or whether it came from my car. I had my suspicions but the tyre monitor showed no problem. As soon as I got onto the dual carriageway it was clear something was amiss. I pulled off at the next exit and checked the rear tyre and it was obviously deflated.

That's the problem with runflats, once you know it is damaged you have to do something right there and then. There is no spare or space saver to put on. So it was off across town to the BMW dealer for a set of new "boots" for the rear. I had checked prices just a few weeks before and they were surprisingly competitive.

Move on a few months and I am on the way back from a local shopping trip when I feel a vibration in the steering on the slipway to the very same stretch of dual carriageway albeit in the opposite direction. I was wondering whether I had lost a balance weight of the allow when the tyre deflation alert binged. At least it worked this time. I kept to the 50mph maximum but, to be honest, anything faster would have been uncomfortable. It was too late to fix the tyre so I drove home and went into the dealer in the morning. What was disturbing was the state of the tyre when it came off. There was basically a split right around the inner wall were it met the tread . It looked like this was not as a result of the puncture but the causal factor. The few miles the car had to do fully deflated can't have helped but it still looked a bit scary - scary enough for me to fork out another ?200 on replacing the other front.

The dealer tyre specialist told me that the problem is that if a tyre loses pressure slowly, it won't trigger the sensors. You won't notice anything by eye either because the 45 profile RFTs are so stiff. Unfortunately, having a stiff outer wall and a "soggy" middle puts a lot of stress into the tyre. The geometry on my car at least focussed this stress on the inner wall.

It seems therefore that RFTs are a bit of a one (OK then, two) trick pony. If you have a high speed blow-out I am convinced they make a big difference. The also mean no spare tyre which frees up space and saves weight.

However, they are at a disadvantage doing all the normal things tyres are supposed to do and cost 30% more. It also seems that you must take more care than you would with a normal tyre to monitor pressures because of the way RFTs mask the problems you would expect. Keep trusting your own instincts too, because the tyre monitors are only partially effective. If you feel unusual vibrations or the steering seems to be getting heavier, make sure you do a physical check.

KAF

Your experience is exactly why it is dodgy to repair runflats.

You were lucky, the sidewall damage was obvious, it is not always so.

My rim sprung a leak yesterday, I was glad I had a chocolate button spare wheel so I could leave it to be fixed whilst I carried on.

I would always recommend getting a spare, even if you have runflats.