Tyre pressure query

John Blake said:

Is it the tyre or the inner tube that is the limiting factor when inflating to an adequate
pressure?

Its the tyre. The inner tube will only burst if the tyre allows it to, by splitting or if it has a
hole in it. The tyre can also pop off the rim in extreme cases resulting in a loud bang.

The air is going into the tube so the limiting factor there is how leaky the tube or the valve is.

--

-Alex

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John Blake said:

Is it the tyre or the inner tube that is the limiting factor when inflating to an adequate
pressure?

Tyre.

Quoted message said:

The tyre walls are usually embossed with a tyre pressure range, but when you are pumping the air
in, it is going into the inner tube which is inside. If something is going to burst due to excess
pressure, I would have thought it would be the inner tube rather than the exterior tyre. If not,
what am I failing to understand?

The tube, when encased in a tyre, can take far more pressure than is reasonable to use with the
tyre. An overinflated tyre won't provide enough traction and comfort and may be in danger of blowing
off the rim.

The tube can't expand more than the tyre so it won't burst unless it's faulty or escapes the tyre
(eg. as a tyre bead squirms off the rim - when it will explode with a deafening bang). The rim is
also another limiting factor: rim sidewalls can only take so much before deforming or breaking.

Think about what happens when you blow up a balloon too much. It eventually explodes when it is so
large that the material has stretched so much that it's too thin to contain the pressure. Trap the
balloon inside a rigid box and you won't burst it. A bike tyre is rigid enough not to go on
expanding significantly beyond its normal inflated size as pressure increases.

See the following article, and by the way, note the points about manufacturers recommendations and
front tyres being softer than rears: www.sheldonbrown.com/tyres.html#pressure

~PB

John Blake tried to scribble ...

Quoted message said:

Is it the tyre or the inner tube that is the limiting factor when inflating to an adequate
pressure?

The tyre.

Quoted message said:

The tyre walls are usually embossed with a tyre pressure range, but when you are pumping the air
in, it is going into the inner tube which is inside. If something is going to burst due to excess
pressure, I would have thought it would be the inner tube rather than the exterior tyre. If not,
what am I failing to understand?

The tyre 'holds' the tube together and provides it with the means to act as intended.

Quick 'field experiment'. Take an inner tube on it's own and blow it up. See what happens at even
very low pressures. Pretty quickly the tube expands to way beyond any useful size and would burst if
air was continually pumped
in. Put the same inner tube into a tyre, assuming you didn't burst it, and blow it up again, see
what happens. Yes, it _can_ be blown up to destruction, but it will take far higher pressures
and won't blow up to a non-useful shape and size. An inner tube is merely an airtight balloon
(_Very_ simplistic description) which needs an external structure (the tyre) to keep it from
expanding at higher pressures, and to make it useful.

--
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John Blake said:

Is it the tyre or the inner tube that is the limiting factor when inflating to an adequate
pressure?

The tyre walls are usually embossed with a tyre pressure range, but when you are pumping the air
in, it is going into the inner tube which is inside. If something is going to burst due to excess
pressure, I would have thought it would be the inner tube rather than the exterior tyre. If not,
what am I failing to understand?

The usual problem is that the tyre beads pop off the rim above a certain pressure. When this happens
the tube can expand to a massive size and burst (this happens instantaneously). Used to be a big
problem with steel rims if you hit a pothole and "splayed" the rim slightly - tyres would then pop
off regularly. It happened to me in the centre of Birmingham years ago and I had to stand in the
middle of a roundabout for a full 10 minutes (it was the rush hour) before I could escape to the
pavement and walk home!

"Pete Biggs" <pmelon{remove [email hidden]>typed

Quoted message said:

The tube, when encased in a tyre, can take far more pressure than is reasonable to use with the
tyre. An overinflated tyre won't provide enough traction and comfort and may be in danger of
blowing off the rim.

Quoted message said:

The tube can't expand more than the tyre so it won't burst unless it's faulty or escapes the tyre
(eg. as a tyre bead squirms off the rim - when it will explode with a deafening bang). The rim is
also another limiting factor: rim sidewalls can only take so much before deforming or breaking.

Don't forget that inner tubes can get forced down spoke wells and burst there if your rim tape is
inadequate. Get Velox cloth tape...

--
Helen D. Vecht: [email hidden] Edgware.

Helen Deborah Vecht said:

Don't forget that inner tubes can get forced down spoke wells and burst there if your rim tape is
inadequate. Get Velox cloth tape...

And use an HPx pump.

(Two FAQs for the price of one)

Tim
--
In space no one can eat ice cream

In message <[email hidden]>, Tim Hall
<[email hidden]> writes

Quoted message said:

Helen Deborah Vecht said:

Don't forget that inner tubes can get forced down spoke wells and burst there if your rim tape is
inadequate. Get Velox cloth tape...

And use an HPx pump.

Only when your track pump isn't handy.

On the topic of track pumps, I've just fitted a Topeal Smarthead to my old SKS pump. It works great,
so much easier than fiddling around with adapters. I recommend it to anyone with an old pump.

Not cheap, but then the original pump wasn't either.
--
Chris French, Leeds

"chris French" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

In message <[email hidden]>, Tim Hall
<[email hidden]> writes

Quoted message said:

Helen Deborah Vecht said:

Don't forget that inner tubes can get forced down spoke wells and burst there if your rim tape
is inadequate. Get Velox cloth tape...

And use an HPx pump.

Only when your track pump isn't handy.

On the topic of track pumps, I've just fitted a Topeal Smarthead to my old SKS pump. It works
great, so much easier than fiddling around with adapters. I recommend it to anyone with an
old pump.

Not cheap, but then the original pump wasn't either.
--
Chris French, Leeds

I think the Topeak Smarthead and accompanying hose is the best accessory I've ever bought. I've used
it for several years now on a couple of steel track pumps that were free (were originally part of
the tool kit that came with Lada cars).

However, I was given a portable, rechargeable Bosch car tyre inflator this summer. Expensive and not
environmentally sound but with the Topeak Smarthead it's absolutely brill for pumping up bike tyres
rock hard in seconds. Paul
--
(PS Remove junk to reply)