Puncture Mystery

Elisa Francesca Roselli said:

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well in
the rim. Can I use that wider tube or will it do lasting damage to the
wheel?

You can and it shouldn't. Using inners that are nominally bigger than
the tyre is quite common and doesn't particularly lead to problems
unless there's a /huge/ mismatch. You don't need to worry about how it
fits in the rim as it's the tyre that does the real containment job.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Where you say there are 'blisters' - do you have rim tape covering the
spoke holes on the rim, and is the rim tape wide enough (no gaps that
the inner tube could expand into)?

I had raised 'blisters' which were from the tube escaping into the holes
for the spokes in the rim - down the side of the rim tape. Some were
just raised bobbles, but others led to punctures from chafing against
the hole/tape etc.

--

Velvet

Elisa Francesca Roselli said:

Today I rode the bike in to the office, no problems. At about 11 am, as
I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me to
dismount it again and we discovered exactly the same kind of puncture,
on the brand new inner tube. It is a large, cross-shaped hole, near the
edge where the tube folds.

Would that be on the part of the tube on the "inside" when on the tire?
The rim strip, which keeps the tube from bulging into the holes inside the
rim for the spokes, might be letting the tube bulge into the spoke holes.
If any small bit of a spoke hole is not securely covered by the rim strip,
this sort of flat will keep happening. Some plastic rims strips will
eventually crack at the holes, so look for that as well, and replace the
rim strip if any problems are found. Make sure that the new stip is wide
enough to cover the holes, but not too wide or the tire will be harder to
get on.

Quoted message said:

Today inspecting the new tube, we found two great blisters in the
rubber, on a different place from the puncture. So perhaps this is a
quality thing - poorly made rubber with inbuilt weaknesses. But odd to
have two punctures on two tubes on successive days!

Lots of tubes have odd bulges when pumped up outside of the tire. Not a
big deal.

Quoted message said:

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well in
the rim. Can I use that wider tube or will it do lasting damage to the
wheel?

You can use it. It's not that much too big.

--

David L. Johnson

__o | If all economists were laid end to end, they would not reach a
_`\(,_ | conclusion. -- George Bernard Shaw
(_)/ (_) |

Elisa Francesca Roselli wrote:
.........

Quoted message said:

I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me
to dismount it again and we discovered exactly the same kind of
puncture,
on the brand new inner tube. It is a large, cross-shaped hole, near
the edge where the tube folds.

Folds?

Quoted message said:

When we removed the outer tyre we checked it very thoroughly to make
sure that there was nothing caught inside. We checked the rims to make
sure there was no spoke poking through. Everything was smooth and
nickel-clean.

What could cause that? The only thing I can think was different is
that
I bought a new bike pump in the UK which makes pumping much easier.
Alhtough I took care to pump up to 5 bar (the specs on the wheel say
between 4.5 and 6.5) perhaps the indicator is not accurate and I
overpumped?

Even if no spokes are poking through, rim tape could be to blame if the
spoke holes are recessed. The higher pressure could have forced the tube
too far down a hole. Good rim tape such as Velox can take very high
pressure. Basic rubber tape can't, always.

Quoted message said:

Today inspecting the new tube, we found two great blisters in the
rubber, on a different place from the puncture. So perhaps this is a
quality thing - poorly made rubber with inbuilt weaknesses. But odd to
have two punctures on two tubes on successive days!

The main part of the rubber (or butyl) itself won't be weak. However,
poorly made/designed tubes can have weaknesses or inadequate reinforcement
around the valve.

Quoted message said:

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well
in
the rim. Can I use that wider tube or will it do lasting damage to the
wheel? Otherwise I have to wait for the spares to come from the UK
every time and my current supplier is the one whose tubes keep
popping. As an internet buyer I have no way to check the quality in
the shop before I
buy, so I am easy to diddle.

The wider tube will cause no problems as long as you can stuff it in there
without damaging or trapping it. In fact, it'll be more durable and hold
air longer. Narrow tubes are certainly easier to fit, though, and weigh
less, of course.

~PB

Elisa Francesca Roselli said:

Yesterday as I was all dressed up and ready to set out on my Dahon
Impulse P21, I discovered that the front wheel was completely flat. This
was odd, because I had pumped it the day before and test-ridden it
around my underground parking a few times. It had been fine.

In the evening, a colleague helped me change the inner tube. We put in a
brand new one. We discovered an enormous puncture in the old one.

Today I rode the bike in to the office, no problems. At about 11 am, as
I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me to
dismount it again and we discovered exactly the same kind of puncture,
on the brand new inner tube. It is a large, cross-shaped hole, near the
edge where the tube folds.

What is "where the tube folds"? Are you using a tube that is far too
big, so it has to fold up to fit in the wheel?

Other than that, it sounds like a rim tape problem. Are there big divots
over the spoke holes where the tape has stretched (I assume you have
some tape there in the first place)?

James

Elisa Francesca Roselli said:

Yesterday as I was all dressed up and ready to set out on my Dahon
Impulse P21, I discovered that the front wheel was completely flat. This
was odd, because I had pumped it the day before and test-ridden it
around my underground parking a few times. It had been fine.

In the evening, a colleague helped me change the inner tube. We put in a
brand new one. We discovered an enormous puncture in the old one.

Today I rode the bike in to the office, no problems. At about 11 am, as
I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me to
dismount it again and we discovered exactly the same kind of puncture,
on the brand new inner tube. It is a large, cross-shaped hole, near the
edge where the tube folds.

When we removed the outer tyre we checked it very thoroughly to make
sure that there was nothing caught inside. We checked the rims to make
sure there was no spoke poking through. Everything was smooth and
nickel-clean.

What could cause that? The only thing I can think was different is that
I bought a new bike pump in the UK which makes pumping much easier.
Alhtough I took care to pump up to 5 bar (the specs on the wheel say
between 4.5 and 6.5) perhaps the indicator is not accurate and I overpumped?

Today inspecting the new tube, we found two great blisters in the
rubber, on a different place from the puncture. So perhaps this is a
quality thing - poorly made rubber with inbuilt weaknesses. But odd to
have two punctures on two tubes on successive days!

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well in
the rim. Can I use that wider tube or will it do lasting damage to the
wheel? Otherwise I have to wait for the spares to come from the UK every
time and my current supplier is the one whose tubes keep popping. As an
internet buyer I have no way to check the quality in the shop before I
buy, so I am easy to diddle.

Many thanks

EFR
Ile de France

"cross-shaped hole" That sounds to this non-expert like a true blow-out (which
you indicated it was), not a simple puncture. But tube was (supposedly)
contained by the tire. So how does a tube inside a tire blow out? Everything
I've read said this is impossible (or "unpossible", as a Bavarian ski instructor
once said to me). What does the bead of that tire look like? Is it 100% even
and smooth?

Elisa Francesca Roselli said:

Today I rode the bike in to the office, no problems. At about
11 am, as I was sitting calmly at my desk beside it, I heard a
little explosion. Lo and behold, the front wheel was flat again.
My colleague helped me to dismount it again and we discovered
exactly the same kind of puncture, on the brand new inner tube.
It is a large, cross-shaped hole, near the edge where the tube
folds.

When we removed the outer tyre we checked it very thoroughly to
make sure that there was nothing caught inside. We checked the
rims to make sure there was no spoke poking through. Everything
was smooth and nickel-clean.

<snip>

Quoted message said:

Today inspecting the new tube, we found two great blisters in
the rubber, on a different place from the puncture. So perhaps
this is a quality thing - poorly made rubber with inbuilt
weaknesses. But odd to have two punctures on two tubes on
successive days!

It's not a problem with the tubes as such. If you heard a bang then
it's a sure thing that part of the tube was at that moment outside the
chamber made by the tyre and the rim. The blisters in the tube indicate
that bubbles are forming somehow. The tube is not strong enough to
resist the formation of the bubbles, and it's not meant to be.

It sounds like the tube is either escaping from under the tyre bead, or
being forced down into into the spoke holes. Check the tyre bead (the
bit that you have to lever over the rim to get the tyre on and off) for
damage, look closely at the tape that lines the rim and covers the
spoke holes, and check the rim itself for damage. If there are no
problems there just be very careful that the tube is completely inside
the tyre before inflating it. Push the tyre wall away from the rim all
round its circumference. You should not be able to see the tube at all.

A slightly oversized tube should not be a problem as long as you can
get the tyre on without pinching it anywhere.

--
Dave...

--
Dave...

Elisa Francesca Roselli said:

Today I rode the bike in to the office, no problems. At about 11 am, as
I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me to
dismount it again and we discovered exactly the same kind of puncture,
on the brand new inner tube. It is a large, cross-shaped hole, near the
edge where the tube folds.

Do you inflate the inner tube slightly before replacing it in the
tyre, and make sure it's not trapped by the tyre as you put the tyre
back into the rim?

Trapped inner tube is the reason my otherhalf experiences explosions
after mending his punctures (our poor cats' nerves are shattered).

James Annan <[email hidden]>typed

Quoted message said:

Other than that, it sounds like a rim tape problem. Are there big divots
over the spoke holes where the tape has stretched (I assume you have
some tape there in the first place)?

Sounds BANG like a rim tape problem to me too. Get Velox...

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

Pete Biggs a écrit :

Quoted message said:

Elisa Francesca Roselli wrote:

It is a large, cross-shaped hole, near

Quoted message said:

Quoted message said:

the edge where the tube folds.

Folds?

All I mean is that when you first buy a tube, it is folded into a flat
strip to compress it into a little box. I mean that the tear is near
that. No the tube was not folded inside the rim.

EFR
Ile de France

Peter Clinch a écrit :

Quoted message said:

Elisa Francesca Roselli wrote:

Can I use that wider tube or will it do lasting damage to

Quoted message said:

Quoted message said:

the wheel?

You can and it shouldn't. Using inners that are nominally bigger than
the tyre is quite common and doesn't particularly lead to problems
unless there's a /huge/ mismatch.

Unfortunately, I just tried it and it won't go on at all. It seems not
only too wide but also much too long for some reason. It says 20" on it,
but in fact there is an enormous excess of about 6" that I cannot pinch
in without gathering it like a skirt.

EFR
Ile de France

Elisa Francesca Roselli said:

Unfortunately, I just tried it and it won't go on at all. It seems not
only too wide but also much too long for some reason. It says 20" on it,
but in fact there is an enormous excess of about 6"

That'll be the wrong tube in the right box then. take the wheel into
the shop when you get the replacement and check it there and then.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Elisa Francesca Roselli said:

Unfortunately, I just tried it and it won't go on at all. It seems not
only too wide but also much too long for some reason. It says 20" on
it, but in fact there is an enormous excess of about 6" that I cannot
pinch in without gathering it like a skirt.

Stupidly, there are three completely different sizes called "20 inch".

See http://www.sheldonbrown.com/tire-sizing.html

~PB

"Elisa Francesca Roselli" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Yesterday as I was all dressed up and ready to set out on my Dahon Impulse
P21, I discovered that the front wheel was completely flat. This was odd,
because I had pumped it the day before and test-ridden it around my
underground parking a few times. It had been fine.

In the evening, a colleague helped me change the inner tube. We put in a
brand new one. We discovered an enormous puncture in the old one.

Today I rode the bike in to the office, no problems. At about 11 am, as I
was sitting calmly at my desk beside it, I heard a little explosion. Lo
and behold, the front wheel was flat again. My colleague helped me to
dismount it again and we discovered exactly the same kind of puncture, on
the brand new inner tube. It is a large, cross-shaped hole, near the edge
where the tube folds.

When we removed the outer tyre we checked it very thoroughly to make sure
that there was nothing caught inside. We checked the rims to make sure
there was no spoke poking through. Everything was smooth and nickel-clean.

What could cause that? The only thing I can think was different is that I
bought a new bike pump in the UK which makes pumping much easier. Alhtough
I took care to pump up to 5 bar (the specs on the wheel say between 4.5
and 6.5) perhaps the indicator is not accurate and I overpumped?

Today inspecting the new tube, we found two great blisters in the rubber,
on a different place from the puncture. So perhaps this is a quality
thing - poorly made rubber with inbuilt weaknesses. But odd to have two
punctures on two tubes on successive days!

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well in
the rim. Can I use that wider tube or will it do lasting damage to the
wheel? Otherwise I have to wait for the spares to come from the UK every
time and my current supplier is the one whose tubes keep popping. As an
internet buyer I have no way to check the quality in the shop before I
buy, so I am easy to diddle.

Many thanks

EFR
Ile de France

As an aside...
My friend and I had a situation where a reasonably high pressure tyre was
put into a very hot car (had been parked in the sun all day) and then blew
out - explosion stylee - whilst we were sat in traffic.
The only explanation for this mystery is the rapid expansion of air in the
hot vehicle - nothing else had changed.
We've had it happen twice now (once when the tyre was left in the vehicle
all day), and so now partially deflate tyres if they're to be in a hot
environment like the inside of a car.
Makes you wonder what people are thinking when they leave a dog in a car
(thankfully they don't explode though, I suppose).

AndyC

AndyC said:

Makes you wonder what people are thinking when they leave a dog in a car

That's the trouble. They're not thinking.

In article said:

Elisa Francesca Roselli said:

Unfortunately, I just tried it and it won't go on at all. It seems not
only too wide but also much too long for some reason. It says 20" on
it, but in fact there is an enormous excess of about 6" that I cannot
pinch in without gathering it like a skirt.

Stupidly, there are three completely different sizes called "20 inch".
See http://www.sheldonbrown.com/tire-sizing.html

And a size (500A) that isn't called 20 inch in between the ones that are.

But 440 and 451 can use the same inner tubes, and I'd expect 406 and
419 to, and a 451 tube in a 406 tyre still isn't going to give 6" spare.

AndyC said:

As an aside...
My friend and I had a situation where a reasonably high pressure tyre was
put into a very hot car (had been parked in the sun all day) and then blew
out - explosion stylee - whilst we were sat in traffic.
The only explanation for this mystery is the rapid expansion of air in the
hot vehicle - nothing else had changed.
We've had it happen twice now (once when the tyre was left in the vehicle
all day), and so now partially deflate tyres if they're to be in a hot
environment like the inside of a car.

As well as the increase in pressure in the tyre, the tube might be
significantly weakened by the higher temperature.

--
Joe * If I cannot be free I'll be cheap

Elisa Francesca Roselli said:

Yesterday as I was all dressed up and ready to set out on my Dahon
Impulse P21, I discovered that the front wheel was completely flat.
This was odd, because I had pumped it the day before and test-ridden
it around my underground parking a few times. It had been fine.

In the evening, a colleague helped me change the inner tube. We put
in a brand new one. We discovered an enormous puncture in the old one.

Today I rode the bike in to the office, no problems. At about 11 am,
as I was sitting calmly at my desk beside it, I heard a little explosion.
Lo and behold, the front wheel was flat again. My colleague helped me
to dismount it again and we discovered exactly the same kind of
puncture, on the brand new inner tube. It is a large, cross-shaped hole,
near
the edge where the tube folds.

When we removed the outer tyre we checked it very thoroughly to make
sure that there was nothing caught inside. We checked the rims to make
sure there was no spoke poking through. Everything was smooth and
nickel-clean.

What could cause that? The only thing I can think was different is
that I bought a new bike pump in the UK which makes pumping much easier.
Alhtough I took care to pump up to 5 bar (the specs on the wheel say
between 4.5 and 6.5) perhaps the indicator is not accurate and I
overpumped?
Today inspecting the new tube, we found two great blisters in the
rubber, on a different place from the puncture. So perhaps this is a
quality thing - poorly made rubber with inbuilt weaknesses. But odd to
have two punctures on two tubes on successive days!

Another question: the size spec for this inner tube is 35-406, or 20 X
1.35 in Imperial. I'm very worried that I will not be able to find
replacements in France. A visit to Go Sport at lunch produced only a
37-406, 20 X 1.5 tube which seems far too wide and does not fit well
in the rim. Can I use that wider tube or will it do lasting damage to the
wheel? Otherwise I have to wait for the spares to come from the UK
every time and my current supplier is the one whose tubes keep
popping. As an internet buyer I have no way to check the quality in
the shop before I buy, so I am easy to diddle.

You ruled out projecting spokes, although from what you say - especially the
shape of the puncture, and the fact that you got two similar ones - it would
appear likely to be caused by metal of some kind.

One other possibility is a damaged tyre, and the inside is chafing away at
the tube. I once had to discard a tube which had worn away in several
places, and was as a result leaking like a sieve. Also I've had problems
with Kevlar reinforced tyres which play havoc with the tube unless it's is
pumped up to the "recommended" pressure - impossible with a handpump. Ironic
given that the idea is to _prevent_ punctures!

I had a tube explode on me once. My fault entirely. The tyre was worn - in
fact so badly that a hole developed which the tube managed to penetrate.
Rather like bubble gum, it ballooned out then exploded with a sound like a
gun going off. The car driver overtaking me at the time wondered what on
earth had happened!

One nasty experience was when I bought a replacement tube from Halfords.
Miles from the nearest LBS I needed it, only to find that it had a hole
about 5mm diameter in it!

Brian

Thanks to all for the suggestions. I've also been looking at what Jobst
Brandt has to say on the subject.

I think that when I put in the second tube I did not do it correctly. It
is more than likely that it was not properly encased in the rim.

Yesterday I put in a third tube. This time I took the tyre right off,
pushed the tube well up into it and then popped it back onto the rim,
pushing the valve through the hole. Don't know if that was correct and
if it won't explode again.

In fact, when I put the wheel back on I noticed other problems. There is
a distinct hesitation on the bike. It does not roll properly and freely,
forward and back. It is as if the brake were stuck. I think I did not
centre it properly when I put it back in the fork, and that it is too
close to the brake pad on one side. In general, it doesn't feel right.

So I've decided to take it to a Remote Bike Shop on the weekend for a
general tuning and checkup (LBS [censored] refuses to service any bike that
he hasn't sold himself). It's a palaver, but I've had the bike for about
6 months now, don't know a rat's ass about proper maintenance, and am a
little too heavy to ride it, so a general tune-up is probably in order.

I've also ordered some new inner tubes and rim tape from the UK (Dahon
bikes are not supported in France).

EFR
Ile de France