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I have a mountain bike with 2 sets of tyres, a road set and off road set, when I switch between them about 1 in 3 times I seem to get a puncture, and I can't see why? I've gone though 4 innertubes now doing this.

So I'll inflate the tyre, cycle around for 30-40mins then I'll notice something wrong, and it's almost flat?

Am I doing something wrong? I deflate the tyre, flick off the tyer and innertube (using a plastic thingy from Evans, so no sharp bits there), put the innertube inside the other tyer, put both back on the wheel and inflate.

Any help would be appreciated, if I don't reply right away I'm probably walking down the cycle shop buying another innertube. :-)

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What is a "plastic thingy from Evans"? It definitely is possible to damage a tube with a plastic tire lever. The other thing you could be doing is not getting the tube properly positioned -- could be twisted or could be that the stem is not properly positioned and is being stretched. –  Daniel R Hicks Oct 1 '13 at 15:17
    
A bit more detail would help. Are you partially inflating the tube before mounting the tire? Are you using a single tire lever or multiple levers? Also, are your tires the same size? Different size tires require different tubes. And where are your punctures showing up? Are they on the same place on the tube every time? Near the valve, or somewhere else? Also, see these: bicycles.stackexchange.com/questions/17750/… and bicycles.stackexchange.com/questions/4602/… –  jimirings Oct 1 '13 at 15:22
    
sorry for my bad description of the plastic thingy from Evans, lol it's the same jimirings added a link to bicycles.stackexchange.com/questions/17750/… thanks guys I might double check I'm not pinching the inner tube, I've kept back 2 broken innertubes to do the put 'in a bowl of water' test and check for bubbles. I'm sure almost 100% the tyres are the same size. –  Mark Oct 1 '13 at 15:57
    
Is it always front? or always rear? i.e. could it be down to a particular wheel? Also, this doesn't help your immediate problem, but I invested in a second set of wheels - far less faff to change a wheel than a tyre. Just a thought. –  PeteH Oct 2 '13 at 8:52
    
You know that you can repair inner tubes don't you? Get some patches next time you're down at the bike shop. –  stib Oct 9 '13 at 11:41

1 Answer 1

A theory: There is some damage or debris on the inside of your tire. A second theory is slightly out of position rim tape. A third theory is your technique may be leading to a pinch flat.

Questions to help diagnose: When you switch between tire sets, does the flat happen only going to one set of tires? Or does it happen no matter which tire? If it's just one tire set, then inspect the inside carefully for debris or other issues.

Next time the tire is off, look at the rim tape carefully and run a finger along it. It should be smooth and sturdy. You may also want to check that it's secure all the way around. If it is moving around during tire changes it could be exposing a spoke nipple.

The third theory would be that if the tire it tight or tough to get on then perhaps you are pinch flatting during the tire change. Advise here is to go carefully...

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Additionally, something else to avoid pinch flats, is inflating to about 20psi, releasing the air, pulling the tire away from the wheel all the way around and reinflating –  JeffS Oct 1 '13 at 16:13

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