bicycle front tire keeps blowing out?

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skadanks

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I have a mountain bike I use both for off-road rides and just running errands around the neighborhood. In the last 2 weeks, my front tire had blown out 4 times. Every single time, the tear in the rubber had occurred right at the base of the presta valve. I checked for sharp metal on the rim that could be causing it and I can find nothing. Today, it had disastrous consequences. Was riding, it blew out, I lost control and flew over the handlebars and scrapped myself up pretty bad. I can't find anything visibly wrong that keeps causing these tears in the innertube at the base of the valve. I've owned the bike since 2001and have never had problems with rapid decompression in my tires. I've used a Mt. Tuffy insert to protect against thorns for the last year, but I doubt that would be the problem or I'd have been getting it all along, on both tires.

Any ideas what the cause could be?
 
I've experienced the same situation over and over again but haven't yet found any one thing that might be the answer. I can tell you a few things I've done to try to alleviate it however.

First - when installing the tube be extra careful as you insert the stem into the wheel to be sure you don't pinch it between the bead of the tire and the rim. Second - when first inflating the tire after installation, screw on the retainer ring but not all the way to the bottom of the stem. Leave a few threads at the bottom, this allows you to place the air chuck onto the valve without placing undue stress on the connection between the stem and the tube. Third - don't buy the cheapest tubes... my experience has been that this seems to occur more often on the cheaper ones.

I believe the reason it happens is that the presta, unlike the Schrader valves, have a brass flange where the stem meets the tube and that any excessive pressure down or to the side of the stem can cause the metal portion to pinch the tube causing a weak spot that sooner or later gives out.
 
try a different brand of tubes
pumping up your tyres about 60% when you mount your tyre on again and see if it mounted properly, deflate and then pump to ideal pressure
check the tyre liners or rims for sharp debris, glass goat heads etc
also check the tyre for debris as well
I hope that helps
I have wheelsets that get constant flats and if i do these things they usually stop
 
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