Valve stems breaking from tube.

[Allydoug]

Hi, does any one know why so many stems are breaking off form their tubes?
I have had many more flat tyres due to this than 'normal' punctures recently . Maybe someone has a fix to stop this happening or to fix the broken ones. I think it was Mark Beaumont who said that if you attach the nut on the rim to hard then this often happens, so I have made sure this not too tight.
Any suggestions would be very welcome!

[mjr]

Sharp edge on the hole in the rim? Dud batch of tubes? Pump without a hose between it and the valve?

[Brucey]

there are occasional bad batches of tubes out there, (and underinflation can do it too) but this problem very often occurs because the rim is the wrong sort (presta valve in a Schrader/woods hole) or the rim manufacturer has drilled the inner wall of a 'presta' rim to the same size as a Schrader valve.

The result is that the rim tape alone is asked to support the valve and it can't do it.

A good-ish (and easy) fix is for this to use the locknut from a recent schwalbe presta tube and to fit it to the tube before you fit the tube to the tyre. This locknut has a shoulder on it which engages nicely with most rims.

A better fix is to fit a ferrule in the rim, under the rim tape. Mavic and 'Problem solvers' make suitable ferrules for this purpose.

In a well-designed installation there is a tiny shoulder on the metal part of the valve stem and this won't pass through the inner wall of the rim. As soon as the load is on the rubber around the stem rather than the stem itself you are more likely to pull the valve out of the tube. Using a locknut as per normal (I.e. on the outside) certainly won't help either.

hth

cheers

[Allydoug]

Thanks for your contributions I'll think about those ideas/sujestions!
Myself