What’s causing my mystery puncture?

Published: 29 September 2010

Q. I was riding on the M54 tonight and the front tyre on my 2008 Kawasaki ZX-10R went flat really quickly, I struggled over to the hard shoulder and got recovered back home.

I expected to find something sharp hanging out of the tyre but nothing. So I got the foot pump out and re-inflated the tyre and it doesn’t seem to have a puncture.

I’ve pumped it up to 50psi with still no leaks from the tyre or valve, I haven’t got a clue what’s caused this very worrying problem and any advice would be greatly appreciated
Bicster, MCN technical forum

A. Although the valve seems to be holding now, it can be a different matter when your wheels are spinning round hundreds of times a minute at high speeds and it’s having to cope with the centripetal force.

Tyre valve springs can weaken with age, old valve rubber can perish and, like tyres, they can also be affected by solvents/polishes.

Valves are almost universally replaced when you have new car tyres fitted, but it still doesn't appear to be the case with motorcycle tyre replacement.

You should also use valve caps. When Bridgestone carried out a test at Cadwell Park, going for it on a bike without valve caps, the tyres had started to deflate in two laps.

The best are steel caps with rubber O-rings (aluminium caps can corrode to the steel valve stem and are then a real pain to get off). At a push you can use plastic caps with O-rings.

But under no circumstances should valve caps without O-rings be fitted, they're your last line of defence against leaking air. Stick to plain steel ones and not ‘customised’ ones, those flashing lights and dice are irresistible to thieving kids.

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