Tyre pressure.

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Phil66
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Joined: 10 Jul 2009, 9:46am

Tyre pressure.

Post by Phil66 »

Just popped an inner tube. I may have over inflated it to about 70 PSI, the max on the tyre wall says 60 PSI, would that have been the reason. I'd cycled about 2 miles before it went bang!
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Vantage
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Re: Tyre pressure.

Post by Vantage »

Doubtful. Unless maybe the tube was way too small for the tyre.
What condition is the tube and tyre in? Is the valve still attached? Are there any tears in the tube or tyre, unsightly bulges?
I wouldn't have thought an extra 10psi would have in itself caused the blowout given that even at the tyres max, it also has to endure the riders weight and shocks from the surface it tracks, rim temperature due to braking and all sorts of other stuff I can't even think of atm.

Might be worth posting this same question in the Bikes and Bits - Technical Section for more/better answers.
Bill


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531colin
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Re: Tyre pressure.

Post by 531colin »

Phil66 wrote:Just popped an inner tube. I may have over inflated it to about 70 PSI, the max on the tyre wall says 60 PSI, would that have been the reason. I'd cycled about 2 miles before it went bang!


What usually happens is a short length of the tyre lifts out of the rim, so the tube bulges out, and of course the tube can't stand the pressure without the tyre to support it, so it bursts.
Cause can be tyre poorly seated (ie lopsided, so one part is too low, too high elsewhere) or some mis-match between tyre and rim...over-size tyre, under-size rim.
Rim type is important, a tyre rated at 60 for a hook bead rim will stand less pressure on a straight rim.....

Image

60 is a pretty low rating, what tyre is it?
Phil66
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Re: Tyre pressure.

Post by Phil66 »

Sorry for not coming back sooner.

Tyre is one I got in France called a GRL CRUZ on an Alex Rim. The Tyre is meant to be the next best thing to a Schwalbe Marathon Plus, if you believe what you're told by the bloke selling it to you.
cotswolds
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Re: Tyre pressure.

Post by cotswolds »

Have you checked to see if it's a rim tape problem?

I've had a couple of punctures like this, once with an incorrectly seated rim tape, and I think the other time was after I got my first track pump and started using higher pressures. In both cases I covered quite a few miles before the tubes went.

Easily diagnosed by looking at the location of the puncture.
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al_yrpal
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Re: Tyre pressure.

Post by al_yrpal »

I had this happen too recently. I had inadvertantly put a tube in that was too small for my 37mm tyres. Went like a pistol shot and split for about 4 inches near the valve. Check that the inner tube is the correct size.

Al
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andrew_s
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Re: Tyre pressure.

Post by andrew_s »

If it goes BANG!, it's because the tube has escaped from inside the tyre, either through a cut, or underneath the bead.
It's usually because a section of the tube was trapped between the tyre bead and the rim when the tyre was fitted. BANG! can happen either during pumping, or a short time afterwards. Sometimes you can see the bubble of tube start to form and get to the valve in time to prevent BANG!, but it's unusual.
You get delayed BANG! because the pressure of the tyre bead against the rim is enough to mostly seal off the bit of tube that's on the outside, but flex whilst riding allows small puffs of air through until there's enough pressure outside to start to lift the bead away from the rim, giving a rapid run-away to BANG!

You ought to stop pumping at about 5spi, and go round the tyre on both sides pushing the bead back from the rim to check that the tube isn't trapped, but even if you know you should, this step is often skipped.

Incorrectly sized tubes don't give a problem in themselves, but it is easier to trap the tube if it's not the right size.
The trapped bit of tube is usually close to where you finished fitting the tyre
Phil66
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Re: Tyre pressure.

Post by Phil66 »

Thanks all for your replies. I had rode 300miles since fitting the tyre and tube, but only a couple of miles since putting a bit more air in it. On closer inspection I can see that there’s wear on a small section of the rim of the tyre. I’m guessing that part of the tyre rim popped out and that led to my problems. Like the previous post says, I’ll need to check for that each time I inflate my tyres, but probably won’t.

Cheers all.
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