What’s caused my tyre valve to blow out?!

Last week I had what I think was a fairly lucky escape. I was checking the tyre pressures on my 2001 Honda CBR1100XX, but when I put the tyre gauge on the valve stem the stem itself (thread included) blew through the rubber mounting in the wheel rim which stayed in place. It seemed my minor disturbance of the valve caused something to let go inside.

This has to have been an incredibly dangerous condition given the Blackbirds potential for huge speeds. The tyre was already fitted when I got the bike so I don’t know who fitted it, or if new valves were indeed fitted. My guess is maybe they were not. The bike has done low miles 17,000 for a 10-year-old bike. Can over pressurising the tyre cause this? In 32 years of riding this is a first for me.
Geoff Hillier, Ashford, Kent

 
You can’t discount faulty manufacture for the valve, however the all-important sealing of the valve stem is carried out by rubber, and just like the tyre itself, that rubber can perish, especially if it’s stored in less than ideal conditions. Any environment that has an excess of ozone, on the coast, or even in a garage with an electric motor running, for say a lathe, will create ozone which will attack the rubber.

A good rule of thumb for tyre life is five years from purchase, as for the stems, make sure they are replaced as a matter of course every time your tyres are changed and it should be at least another 32 years before it happens again.