I've had a couple of punctures recently. For me, this is really a rare anomaly. I ride a lot, on several different bikes/tyres, and generally I don't get punctures. In fact, up until last year, I can only remember having one puncture in more than 30 years of riding. Now in a just a couple of months I've had another two...
Which causes me to speculate on how the recent punctures occurred.
Some (pertinent?) background: I bought the 1979 R100RS in May 2012, so I'm unsure of the age of the tyres/tubes, but they were/are obviously old. The front, which punctured, is a Metzler ME33 Lazer. It has an older-style ME33 branding and is made in Germany. The current ME33s are made in Brazil and are branded differently. I'm unsure how long since the old style tyre was available but I suspect it's been at least five years, and possibly up to 10. Despite it's obvious age the tyre has performed without fault (on dry roads). It's now toast and will be replaced asap.
The first puncture (December): It happened when i was taking the bike to get a new rear tyre fitted (I know, the irony
). It was a warm day, I had ridden for about an hour. The tyre went totally flat while crawling in traffic on a freeway (and just about to enter a tunnel!). I managed to get off the freeway and through inner city traffic safely (phew!). On attempting to re-inflate the tyre would not hold air. On removing the tyre the tube was found to have a small hole. There was no obvious penetration mark or object in the tyre/tube. But i did find some small hard grains in the tyre. I didn't check them closely but (later) came to think that they could have worn through the tube causing it to deflate... they might have been grains of sand? The tube was replace with a new one.The second (last week): The flat tyre was discovered when I'd stopped to refuel after a three hour ride. After parking the bike and having lunch I came back to it to find the front tyre flat. The ambient temp was quite hot. At the tyre shop a leak was identified. On checking, once again, no obvious penetration or object was found, but another small grain of 'hard stuff' was discovered (but once again not thoroughly inspected, d'oh!).
So, I was wondering: Can a small grain of sand lodged between a tyre and a tube rub through the inner tube and cause it to deflate? It sounds logical to me but what do ppl think? Has it happened to anyone? I thought it could have happened to an old (hardened) tube but the second puncture occurred with a tube only a couple of months old. Or was it just a coincidence
No matter: I'm definitely getting a new (clean) tyre and tube fitted before the next outing...
I'd be curious about the grainy stuff and how it got in there.