2 blow outs in quick succession?

carrock

strange.

Running schwalbe ultremo zx 25c with specialized ultralight turbo tubes 18/23

Running at 105 front 115 rear as I am 17 stone-ish

And have had 2 punctures in the last week or 2 where the rear tube has popped and pushed the tyre partly off the rim.

No sign of a foreign object in the tyre

Has happened just after reinflating the tyres, so I'm assuming its a combination of my portliness, thin tubes and big tyres together with fairly high volume and pressures.

But I have been running exactly the same setup for 2 or 3 years, and haven't suddenly put a stone or 2 on....

I did wonder whether its the time of year ( hedgecutting season ) but both times my wife has been cycling with me and had no problems....

Any ideas?

marksteven

tyre's not seated properly , trouble with really thin tubes. blow a little air in with ya mouth & check you cant see any tube , few pumps check again , sorted

carrock

cheers will try that

slowbike

You're using 25 tyre with tubes designed for 18/23?
I'd replace the tubes with the next size up.

carrock

Slowbike wrote:

You're using 25 tyre with tubes designed for 18/23?
I'd replace the tubes with the next size up.

Yes I was thinking thin tubes inflated to maximum pressure, oversize, with a heavy weight- all contributing factors

sungod

the tubes being slightly undersized, or high weight/pressure (within design limits) won't cause blowouts

the cause is is almost certainly that the tubes were nipped between rim and tyre when fitting - it can also be due to rim/tyre wear/damage but that's much less common

once inflated, the air will force it's way into the pinched section, eventually lifting the tyre and allowing the unrestrained tube to expand and burst, this can happen during inflation or over a much longer period

it's much easier to nip lightweight tubes

inflate the tube just enough to round it out before fitting, that greatly lessens the chance it'll get caught

bobones

I now make sure the partially inflated tube is seated in the rim all the way round the wheel before seating the tyre. I find this helps dramatically in reducing the chances of pinching the tube.