Puncture mystery

Jim Newmark

This is a last resort. I thought I knew about bikes but this has me stumped. Back (driving) wheel of a Trice (20" x 1.95") Maxxis Ringworm tyre, designed for up to 110psi. No problems until an unexplained puncture, 1" from the valve and also on the inner aspect. No sign of damage to the rim tape and no protruding spoke. OK, just replace the tube - whoops, immediate puncture at 90psi, another look, identical puncture, oatched this time, and exactly the same thing with a hole through the patch, and no damage to the underlying tape. And once again. So into Halfords - you have supplied me a faulty patch of tubes - oh no we haven't sir, just leave the wheel with us and we will sort it. Back to Halfords that evening, I see what you mean sir, we have just gone through three of our tubes at 80-90 psi and we can't see anything wrong with the wheel, we must have a faulty set of tubes, here is your money back.
So I buy some more tubes by mail order, play cautious (rather fed up by this time, having gone through lots of tubes) keep it at 75psi, no problems for weeks. Yesterday noticed it was a bit soft, "normal" loss to 45psi, "it MUST have been a faulty batch, I will just blow it to 90psi and see what happens". And b ....me, it blows again, identical hole and still no damage to the rim tape. So now it is back at 75psi and I have no confidence whatsoever that I won't be stranded in the middle of nowhere sometime soon with a flat back tyre and one spare that will blow as soon as I pump it up. Anybody have any ideas at all?

redvee

The rimtape might not look damaged but under 90psi it will give and that is what could be giving you the punctures. Invest in some better quality rimtape or just use insulation tape but go round the rim several times. Finding a quality 20" rimtape might be difficult.

konadawg

Yep, must be that when pressurised the rim tape is being pushed into the spoke holes and "stretching", now since where the valve is it is holed and thus weak, the give is all coming from there so the spoke hole is being exposed via the super stretched valve hole, the tube blows through into the spoke hole and is punctured by the spoke.

Use Velox cloth tape, you cut this to size and it is also self adhesive, does not give noticeably, and you should be OK.

Jim Newmark

Yes, I guess you must be right, but I have had a look at the rim tape again and still can't see anything wrong with it. The valve hole is close, but I cannot stretch it to anywhere near the adjacent spoke insertions, and you would have thought that having a spoke going through into the inner tube so many times would have caused at least an indentation in the tape. That said, an additional layer of insulation tape prior to my getting some Velox tape has made me feel a bit more confident - enough to pump it to 90psi anway, and no now familiar hiss so far. Thanks, I should have thought of that before.

Crapaud

To rule out the rimtape cut out a strip of old tyre or sturdy plastic from eg. a washing-up liquid bottle (sand down the edges to make sure there are no sharp edges) and place it between the inner tube and rim. if you still get a puncture it's not the rimtape.

How many manufaturers of 20" innertubes are there? Is it possible that there is only one meaning that, no matter which brand you buy, a bad batch would cover the range?

giantsasquatch

It obvious the rim is causing the puncture on the inside. Get VELOX tape, it good cushion and it won't move about.

or cut up a old inner tube to half width and fix it down with tape. I ran them at 120PSI for ages before i got velox tape.

redvee wrote:

just use insulation tape but go round the rim several times.

NEVER use electrical insulation tape , even several times. It too thin and flexes. Several layers still end up flat with no cushion with high pressure tubes. Over time it will force it's way through the holes or wear away at the spoke holes and you still end up with punctures.

andrew_s

Some types of plastic rim tape develop splits along their length that only open up under pressure. You'd have to take the tape off to see them, unless pushing the end of a key down into the spoke well will show them.

you pump the tyre up, and the tube expands down into the spoke well, forcing the sides of the split apart. It could be puncturing on the end of the spoke, or it could be the sharp sides of the split rim tape.

mmacavity

http://two-wheels.michelin.com/2w/front ... 44&lang=EN

Jim Newmark

Cracked it - at least I think so. The Velox rim tape did not help - it punctured again since the last posting, in exactly the same place. So I took the wheel and the tube to Bob Jackson cycles, Leeds (thanks guys). They saw immediately that it was a wear / rubbing puncture, and the area on other side of the valve hole was wearing in exactly the same way. It is a 20 inch wheel and the two spoke protrusions that are near the valve (no different in appearance to those all around the wheel, even through the thick Velox tape) happen to fall EXACTLY where the rubber edge to the valve support on the inside of the tube can be felt. It is simply a combination of those factors that repeatedly cause wear and eventual puncture. I will try double Velox tape, or, if that fails, get another rim. I am sure that they are right - it explains everything. Presumably it is unique to 20 inch wheels as otherwise the spokes are further apart. Has anybody heard of this before?

Jim Newmark

No, I didn't fix it. Another identical puncture about 100 miles later. But now I think I HAVE cracked it, thanks to a bike shop in Derby. TheTYRE IS TOO BIG and so revolves on the wheel under traction. This then pulls and stretches the inner tube underneath, which is fixed by the valve, so it splits at the least reinforced point close to the valve, loses air, I open it up but of course, by so doing, it retracts back so the evidence is gone. Sort of the ideal "how to murder an inner tube" mystery - nothing found at post-mortem. The tyre WAS very loose and I could revolve it round when deflated so now I have a new tyre and we will see. Nothing to do with the tape. Has anybody heard of this before?

Ben6899

What make of tyre was it?

Jim Newmark

Ben6899 wrote:

What make of tyre was it?

(20" x 1.95") Maxxis Ringworm tyre, designed for up to 110psi. ICE say that this a familiar problem, 20" is not always the same 20" from country to coutntry as they fairly arbitrarily choose the upper or lower tolderance level

Ben6899

Jim Newmark wrote:

Ben6899 wrote:

What make of tyre was it?

(20" x 1.95") Maxxis Ringworm tyre, designed for up to 110psi. ICE say that this a familiar problem, 20" is not always the same 20" from country to coutntry as they fairly arbitrarily choose the upper or lower tolderance level

Gotta love Conti and their fastidious attention to ETRTO specs...

keef66

Mark the tyre wall next to the valve; you'll soon see if it's revolving.

Jim Newmark

keef66 wrote:

Mark the tyre wall next to the valve; you'll soon see if it's revolving.

Yes, I could have done, but I changed the tyre this afternoon. Actually, I don't want to be proved wrong 'cos then I would be back to square one. I would rather just assume that this is the answer and hope for the best