Left my bike in the garage after riding, and noticed this morning that the front had gone flat. On closer inspection it had done more than that. The inner had burst into a ragged mess, and forced the outer off the rim. The outer is a relatively new Trailraker, which is undamaged, and it was pumped at about 40psi. The tyre and tube haven’t been off the wheel for weeks.
How did that happen then ?

Bead not sitting in rim correctly or to slack. Any fresh damage to the rim that might cause the bead not to sit correctly?

Faulty innertube? front wheel leaning against the heater/radiator?

Voodoo

Your tyres bead was sitting on the innertube, over time it expanded out until it burst.
Pumping up a tyre quickly can do this i.e using gas or a compressor.

sounds like pixies to me

Currently voodoo in first place, closely followed by Oldgit’s suggestion as about the only logical explanation but not sure as hand pumped etc.
Just glad it didn’t do it whilst barrelling downhill 🙁

Yes, bead not correctly seated on the rim.

On pretty much every clincher tyre there’s a band a constant width around the inside of the tyre just by the bead (the wire or kevlar bit that doesn’t stretch and keeps your tyre the same circumference). That band should be visible all the way round the tyre when it’s mounted properly on the rim.

The best way to ensure this, when fitting a tyre, is to pump it up to about 10-15psi and examine the bit between the rim and the tyre – that band should be a constant width. If it’s all wobbly and going up and down as you rotate the wheel, the bead is not properly “clinched” by the hooky bit of the rim.

Sometimes it’s not a problem and people ride on wonky tyres for years. Sometimes as you inflate the tyre, the air pressure forces the bead away from the rim if it’s not seated properly. In spectacular cases, this pushes the bead out and a bubble of inner tube rapidly forces itself between bead and rim, which then explodes with an impressive BANG, shreds the inner tube and sometimes briefly deafens the hapless mechanic inflating the tyre.

I’ve seen it happen a lot of times. It’s most likely when you haven’t checked the tyre properly at low pressure, and it’s easiest to do if you’re inflating from an airline (compressor), especially to high pressures. It’s actually quite impressive to behold but I wouldn’t recommend being very close to it when it happens.

Some tyres are an absolute b*tch to seat properly. The old Specialized Armadillos, and current Schwalbe Marathon Plus (and actually quite a lot of Continentals) were tight and could be a real hassle to fit well. Patience and a bit of tyre-pulling brute force are key.

: P

Yep. When I’m on the road I use Co2, but I give it a puff with a poxy mini pump to seat it first

Be wary of fully inflating a tyre in one go with a CO2 cannister – I’ve heard of the gas solidifying in the valve and holding the valve open when you remove the cannister. You inflate the tyre to 100psi, remove the cannister and it’s back down to 0psi in about five seconds as the valve fails to close and all the gas leaks back out again!

: P

I once changed a puncture on my road bike in my GF’s kitchen. Pretty small, all hard surfaces. Got up to about 80psi before discovering the bead wasn’t seated correctly. Seriously loud bang and ringing ears for a couple of hours and I now check the bead is seated before upping the pressure!

Hehe. Yes, I’ve had a roadie tyre do this on me as I was inflating it – seriously loud bang. Since then I have taken a bit of care when fitting which is why I just don’t get it.
Off to fit a new tube now with ear defenders on 😆

You guys know CO2 is heavier yes?

You guys know CO2 is heavier yes?

Yeah I hear all the Pro’s use helium…

🙂