Tubes severing valves

paul.skibum

Just been out on a short ride (was supposed to be long but the title problem cut it short).

5 miles in short road downhill pedalling in top gear, phssssssssss, tyre flat in a second, tyre off and no puncture just a totally severed valve. Replaced tube with spare but spare tube has bent stem on valve so seems like it might not hold pressure decide on 5 mile route home to be on safe side and not stranded miles from home with dodgy tube.

200 yards from home, phssssssss, tyre down in seconds again, walk home and pop tyre off, same issue valve severed from tube.

Had a problem with something similar once with a very old tyre shifting under braking and pulling the tube round with it severing the stem on the valve hole in the rim. This to me doesnt look similar as the tape hasn't moved, the tube doesnt seem to be pulled round and both times it happened I wasnt braking and had hardly had to brake at all on the ride.

Any thoughts? Tubes were probably a little old - 2 years or so, tyres similar age, wheels Mavic crosstrail.

levolon

my rims "mavic 321" have a small plastic insert at the valve hole for duel fitment ie schrader and presta valve..

if your wheel has this and its got lost fell off? the presta valve is getting cut on the steel rim ??

only other thing i can think of is soap on tyre bead etc so maybe a clean of the bead?

hth

allthegearnoidea

first thing i'd do is look closely at the valve hole area for any 'swarf' etc. it wont take much to do it,
also what pressure are you running in the tyres?? if the tyres rotating under braking then youve not enough pressure in it to seat it properly IMO.

paul.skibum

Thing is though I did 60km in wales on this tyre/tube/rim combo the other weekend so to lose to tubes in 5 miles of gentle hampshire lanes is a bit odd - gonna recheck the tube and tyre but its weird!

bluechair84

+1 for ATGNI, I've seen a valve hole on a new rim with a burr in the metal that was slicing the valve away from the tube. Fortunately, a passing walker had a leatherman. I used the curved tip of the nail file to grind down the burr.