canklecat

This one has me baffled. Any ideas?

This Bontrager standard tube split on the inside, facing the rim. There was no puncture, no pinch flat. The tube was dimpled and wavy along the entire inner side, but the dimples occurred about every inch apart and didn't correspond with the spoke holes. The rim liner was intact. It appears to be a tube flaw. The failure occurred spontaneously, while the bike was in my living room, several days after the last ride. Just a sudden hissing loss of pressure.

There was a cut in the tire opposite this failure, but this was coincidental and had no effect on the tube failure. The cut did not penetrate the tire's puncture shield. There was no damage to the side of the tube facing the cut. Both tires have some similar cuts through the thread that did not penetrate the puncture shield -- no problems with the tube.

(Bontrager standard tube, 700x35-44, 520102150305)






Note dimples spaced about an inch apart on inside of tube. Split occurred in one of the dimples. The dimples don't correspond with the spoke holes in the rim. The rim strip was intact.

*****


Razor thin glass shards cut the thick tread of the Michelin Protek Cross Max down to the 5mm thick puncture shield, but didn't penetrate the shield (which appears to be some sort of fiber or fabric material, possibly similar to Kevlar). I've had several similar cuts and penetrations into the tread but not through the puncture shield. Excellent heavy duty tires for rough roads with lots of debris. (Michelin Protek Cross Max 700x40c).

sreynolds1977

The only time I have had a tube fail on the rim side was a couple of days after a spoke broke in the same area. I assumed that when the spoke failed the release of its tension caused it to poke the tube and even with the rim tape intact, weakened the tube.

cny-bikeman

Only possibility I can think of is stress from low tire inflation and hard acceleration/braking, allowing the tube to shift inside the tire.

canklecat

Bingo. That may be it. Thanks.

I do run these tires below recommended pressure, mostly for comfort. Michelin recommends 75 psi for my weight but that feels harsh so I usually run 50-60 psi.

And I switched to Kool Stop pads a couple of months ago. Braking has gone from a three finger death grip to one finger squeeze. I did lock up the rear wheel a few times getting used to the new brakes, especially on some fast downhill runs, to avoid cars, etc.

I'm not sure I want to increase the tire pressure. I'm pretty satisfied with the ride feel as is. I've eased up on the braking since getting accustomed to the stronger grip of the Kool Stops.

Beyond that I'm not sure what else to try other than heavier tubes or just be prepared to replace them more often.

andr0id

Look at pic 2. There are two very prominent dimples there. When the tube is inflated, it is pushing into something.
Even though your rim strip looks OK, something is going on there. Peel it off and figure out what.

canklecat

Based cny's suggestion, my theory is the tube and rim strip are heating up from hard braking and running at lower pressure, softening, the tube is rippling, and the combination is causing those multiple dimples even where there should be no contact with the spoke holes.

I may try replacing the rubber rim strip with cloth.

Andrew R Stewart 

How much narrower is the tube compared to the tire? If the tube has to expand a bunch to fill the tire the tube stretches some. If the tube had a thin spot (or two) this stretch might exceed the tube's ability to rebound when deflated, and stay stretched. Said stretch point then being so thin might also tear. Andy.

canklecat

These are standard Bontrager 700x35-44 tubes. But the Michelin Protek Cross Max tires are larger than the nominal 700x40 spec -- noticeably wider and taller than my other comparable tires that are 700x38 and 700x42.

Michelin sells Protek tubes that are somewhat square shaped. Those may be a better match for these tires.

However this is my first flat due to failure in a year. That tube was installed by the LBS in April when they installed a new wheel after I warped the original rim. Not bad for a year of riding on rough roads with lots of broken glass, roofing nails and staples, etc.

MNBikeCommuter

It's a new wheel (relatively speaking)? I had a couple of similar mystery flats over a 2-3 month period with a new bike. With the second, I found the culprit: an aluminum shard maybe left over from drilling the valve stem hole.

SkyDog75

If you're using a rubber rim strip on a double-wall rim, that could be your problem.

Rubber rim strips are intended for single-wall rims. They work fine to insulate the tube from sharp edges of spokes & nipples. On double-wall rims, rim strips serve a slightly different purpose. They prevent the tube from expanding into spoke holes and stretching far enough to rupture. To do so, the strip needs to resist stretching and rubber rim strips aren't very good at that.

If you're using rubber strips, replace 'em with cloth tape like Velox or plastic strips like Continental Easy Tape.

canklecat

Yup, it's a double wall rim. Weinmann Zac 19. Got it to replace the warped single wall Alex rim back in the spring.

I'll order some cloth rim tape.

Thanks, all!

cny-bikeman

Cloth will stretch as well

canklecat

I did find a roll of cloth tape in my junk bin but it's too wide. I tried to cut a strip narrower last year but it was a hassle. I'll order some of the Continental Easy Tape HP since it's supposedly stiffer to resist this problem. I would like to continue running those tires around 50-60 psi without worrying about flats.

TGT1

Nipple pimples.

I had one rim / tire combination that developed that problem after a couple of thousand miles. Also wide, (42mm) tires. Narrower tires on the same rim never caused any problems. Does the rim tape show signs of extruding into the nipple holes?

The solution was to install a high pressure Mylar rim tape with the French cloth tape over it. Ether by itself didn't fix it.

Have since upgraded the rim and had no problems.

canklecat

Man, I hate that when that happens. Worst part about adolescence. Next to all the other crappy stuff about being a teenager.

A bit, yup. Very sharply defined impressions from the holes. Good point, I hadn't checked that.

I'm going to try the Continental Easy HP rim strips, which they described as nylon and plastic. Sounds pretty rigid.

SkyDog75

Well yeah, cloth rim tapes like Velox or Newbaum's stretch some -- as do plastic rim strips -- but not enough to let the tube expand into spoke holes and rupture.

canklecat

How rigid is the Continental Easy Tape, or comparable stiffer and thicker rim tape? I'm wondering whether it'll conform to the recess in my rims. The standard rubbery rim strips are 12mm wide. I have some wider cloth tape that will readily conform to the narrower recess so I'll use that for now.