Tuesday 3 September 2013

One inch thorn

Bike maintenance - I need to replace the back rack, although the replacement hasn't arrived yet. But I also noticed that the valve on the back tube was at a 45 degree angle to the radius; this means that the tube has somehow slipped round the wheel, and if that continues, it will sheer off. That happened to me once - instant blowout!

It's easy to fix - I deflated the tube, and worked it back into place, and then reflated the tube.

Or rather, I didn't. It wouldn't pump up. Eventually, after trying a few times, I took the tube out and inflated it, and there was a whooshing of air - a puncture! Just a hole in the outer edge of the tube, as if something had gone through the outer tire. So I ran my fingers round the inside of the outer tire, and found the culprit. I worked it out of the tire, and at first, I thought it wa a one inch nail, but it wasn't, it was a one inch thorn. and it had penetrated straight into the tire.

Even my kevlar tire, gel lining and thorn resistant inner tube wasn't going to stop this big beast. But, easily fixed. I did a puncture repair on the tube, and replaced it with a new one, since they're really quite cheap. I used one of the Giant tubes I bought recently at a bargain price, and as I installed it, I noticed that the tube itself said "Kenda". So it was actually the same thorn-resistant tube I've been very happy with before, only at a much lower price. I got them at at £1.75 each, which is a fraction of the price you'd expect to pay for thorn resistant (i.e., very thick) inner tubes.

But the big mystery is, how come this huge thorn didn't lead to any loss of air from the inner tube? Don't get me wrong, I'm very glad, I really don't like to have to mend a major puncture while 20 kilometers from the car (although when I'm going on a long circuit, I do take with me everything I need to repair a puncture, not that I've ever actually used it). My guess is that I didn't actually have a puncture of the inner tube, the thorn was deflected from it by the armour, but after I deflated and re-inflated the tube, the thorn was able to do its dastardly work as the tube expanded to meet its doom.

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