Cause of puncture

Quoted message said:

Two days ago I fitted a new Michelin Speedium , 700x 23 on my front
wheel and cycled about 20 miles. The tyre was at the recommended
pressure according to my gauge and I'd check all round that the tube
hadn't been nipped by the tyre bead.

Tonight on the way to the start of our ride the tube punctured, just
after I'd leant fairly sharply round a corner. It must have taken 30
seconds for the tyre to go flat.
I couldn't find any cause when replacing the tube. I've just found an
uneven cut 2-3mm long about 2-3mm from the centre line of the tube
where it sits on the rim.

Check for other smaller punctures as well. A slower puncture shortly before
the big one could have lowered pressure without you realising - enough to
make the tyre vulnerable to pinch-flatting.

Quoted message said:

I haven't checked the rim a second time in detail but am wondering
what might have caused the puncture. The spokes are recessed, with a
thick plastic type rim tape fitted. The puncture will I think have
happened against the rim tape.

Any thoughts on the cause and what I should look for when re-
inspecting the rim.

Look and feel for anything sharp or rough at all. Also think about whether
that rim tape really is taking the pressure. Being thick doesn't
necessarily mean it's working. Recommended tape: Velox.

Quoted message said:

The original tube valve wasn't threaded but the replacement is
threaded and has a knurled ring. Should I fit the ring on the valve?

Fit it if it makes your pump easier to use, otherwise don't bother. They
can cause problems if over-tightened.

~PB

Quoted message said:

I couldn't find any cause when replacing the tube. I've just found an
uneven cut 2-3mm long about 2-3mm from the centre line of the tube
where it sits on the rim.

Quoted message said:

thick plastic type rim tape fitted

Remove plastic rim tape and swap for cloth rim tape from your LBS. It's
available in several widths, so it'll help them get your the right one if
you know the inside width of your rims.

email hidden said:

Two days ago I fitted a new Michelin Speedium , 700x 23 on my front
wheel and cycled about 20 miles. The tyre was at the recommended
pressure according to my gauge and I'd check all round that the tube
hadn't been nipped by the tyre bead.

Tonight on the way to the start of our ride the tube punctured, just
after I'd leant fairly sharply round a corner. It must have taken 30
seconds for the tyre to go flat.
I couldn't find any cause when replacing the tube. I've just found an
uneven cut 2-3mm long about 2-3mm from the centre line of the tube
where it sits on the rim.

I haven't checked the rim a second time in detail but am wondering
what might have caused the puncture. The spokes are recessed, with a
thick plastic type rim tape fitted. The puncture will I think have
happened against the rim tape.

I had a spate of similar punctures several years ago. They started
after I had a spoke replaced at my LBS. The tube was being 'cut' by
the sharp edge of the plastic rim tape.

[email hidden] said the following on 10/05/2007 00:31:

Quoted message said:

I couldn't find any cause when replacing the tube. I've just found an
uneven cut 2-3mm long about 2-3mm from the centre line of the tube
where it sits on the rim.

Spoke ends?

Quoted message said:

I haven't checked the rim a second time in detail but am wondering
what might have caused the puncture. The spokes are recessed, with a
thick plastic type rim tape fitted.

OK, not spoke ends, but I don't like the sound of "thick plastic" when
describing rim tape. It should be a thin rubber band, or even better a
cloth type such as Velox. eBay item number 250098486611 is just one source.

--
Paul Boyd
http://www.paul-boyd.co.uk/

Thanks for all the advice. I've just checked the rim again and cannot
see anything rough at all. The rim tape came with the Rigida Flyer
wheel on my 14 month old Giant OCR2, which has done 2000-3000 miles.
This is my first front puncture.

The rim tape is Herrman HPS 16x622-635/28" vh 7. It is a sort of
yellow almost waxy looking plastic seems to be well fitted and has
rounded its self into each recessed nipple eyelet, presumably as the
tape is taking the pressure. As it came with the bike I would be
hopeful Giant used reasonable rim tape, but maybe not.

I'm keen to identify the cause as I was on my last ride before the
Beallach Beag challange around Applecross on Saturday and I want to be
confident I don't have another puncture looming.

Pete's suggestion of a slow puncture reducing pressure to cause a
pinch flat seems most plausible to me. But with water and soap I cant
find any sign of a second puncture.

Thanks everyone.

Ian

Paul Boyd usenet.dont.work@plusnet said:

OK, not spoke ends, but I don't like the sound of "thick plastic" when
describing rim tape. It should be a thin rubber band, or even better a
cloth type such as Velox. eBay item number 250098486611 is just one source.

That looked like an amazing bargain for a minute there, but what
appears to be an auction for a box of rim tapes is actually for a
single roll. :-(

--
Dave...

dkahn400 said the following on 10/05/2007 10:39:

Quoted message said:

That looked like an amazing bargain for a minute there, but what
appears to be an auction for a box of rim tapes is actually for a
single roll. :-(

Yup - a favourite eBay trick, although this one does make it clear what
you're buying in the description. Still £5.30, delivered, for two
wheel's worth isn't really that much considering what we pay for visible
shiny goodies for our bikes :-)

--
Paul Boyd
http://www.paul-boyd.co.uk/

Paul Boyd said:

OK, not spoke ends, but I don't like the sound of "thick plastic" when
describing rim tape. It should be a thin rubber band, or even better
a cloth type such as Velox. eBay item number 250098486611 is just
one source.

Unless putting it on top of some other stiffer tape, a rubber rim band, or
any flexible tape, is no good for recessed holes as pressure from the tube
forces it down the holes. This could make the tube fail even if it doesn't
touch a spoke end.

~PB

On 10/05/2007 11:11, Pete Biggs said,

Quoted message said:

Unless putting it on top of some other stiffer tape, a rubber rim band, or
any flexible tape, is no good for recessed holes as pressure from the tube
forces it down the holes. This could make the tube fail even if it doesn't
touch a spoke end.

You're right of course. I have Velox tape in both of my bikes, and had
forgotten that problem.

Actually, I upgraded my Hardrock so much that I've been able to rebuild
it completely with all the bits left over, and I now seem to have three
bikes :-)

--
Paul Boyd
http://www.paul-boyd.co.uk/

In article <[email hidden]>,
[email hidden]
[email hidden] says...

Quoted message said:

Two days ago I fitted a new Michelin Speedium , 700x 23 on my front
wheel and cycled about 20 miles. The tyre was at the recommended
pressure according to my gauge and I'd check all round that the tube
hadn't been nipped by the tyre bead.

Tonight on the way to the start of our ride the tube punctured, just
after I'd leant fairly sharply round a corner. It must have taken 30
seconds for the tyre to go flat.
I couldn't find any cause when replacing the tube. I've just found an
uneven cut 2-3mm long about 2-3mm from the centre line of the tube
where it sits on the rim.

I haven't checked the rim a second time in detail but am wondering
what might have caused the puncture. The spokes are recessed, with a
thick plastic type rim tape fitted. The puncture will I think have
happened against the rim tape.

Any thoughts on the cause and what I should look for when re-
inspecting the rim.

I wonder if you nipped the tube with a tyre lever, and it took a while
for the weakenend area to fail. Otherwise I'd suspect a gap, split or
sharp edge on the rim tape.

Quoted message said:

The original tube valve wasn't threaded but the replacement is
threaded and has a knurled ring. Should I fit the ring on the valve?

I never use lockrings - the only purpose they serve is to hold the valve
in place until the tube is inflated. They can damage the rim, hide a
twisted tube or pinch the tyre bead against the rim, they tend to work
loose anyway and you have to remove them when fixing punctures.

Paul Boyd said:

On 10/05/2007 11:11, Pete Biggs said,

Quoted message said:

Unless putting it on top of some other stiffer tape, a rubber rim band, or
any flexible tape, is no good for recessed holes as pressure from the tube
forces it down the holes. This could make the tube fail even if it doesn't
touch a spoke end.

You're right of course. I have Velox tape in both of my bikes, and had
forgotten that problem.

Actually, I upgraded my Hardrock so much that I've been able to rebuild
it completely with all the bits left over, and I now seem to have three
bikes :-)

i seem to have ended up with 3 bikes, had one old mountain bike in a
state, one new with nice brakes and springs etc.

and then a cheap town lump for bibling about town.

which really counted as two as the old bike was so knackered.

then moving to london, there is a very local bike shop so i get the old
mountain bike, sorted out and some road tires fitted.

so i have 3 bikes though in truth i very rarely use the new flasher one
as london is rather bereft of stuff to challange it, parks and such can
be taken on the older road fitted one with out a problem, and it feels a
touch silly to ride a off road bike though the parks etc, or at least
compared to what i used it for.

the sensible thing would be to sell it and get a proper racer i guess,
i'll probably just get another bike at some point though....

roger