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Archive for September 15th, 2010

Bicycle Tube: Complete Failure

Glass shard in tire

Glass shard in tire

On my way back from a ride around the block the back tire went pfft thump thump thump. I’m 1.5 miles from home: fix or walk?

The first step: always examine the tire to find the puncture, before you move too far. Finding something sticking out of the tire means you’re well on your way to fixing the flat. Lose the entry point and you’re left to blow up the tire and listen for escaping wind. So I picked up the butt end of the bike, spun the wheel, and this little gem heaved into view…

That area of the road has seen several collisions in recent months that left the shoulder littered with broken automotive glass. The shard in my tire glistened like a diamond, because one side was flat and mirrored; perhaps it’s from a headlamp reflector or side mirror. The pointy end went into the tire, of course…

Glass fragment and puncture

Glass fragment and puncture

Well, a single-point failure like that is easy to fix, so:

  • remember that the hole is a few inches spinward of the label
  • shift to small chainring / small sprocket
  • get the tool bag out
  • lay the bike down (it’s a recumbent, this is no big deal)
  • release the rear brake
  • release the skewer and whack the hub out of the dropouts
  • apply tire irons to get the tire off
  • pop the tube out and examine the innards

No pix of any of that, but suffice it to say I was astonished to discover that the glass penetrated the Marathon tire’s Kevlar belt just barely far enough to poke the Slime tire liner, but not enough to leave more than a hint of a mark on the tube. Definitely not a puncture and certainly nothing that would account for a sudden flat.

That glass shard is not why the tire went flat! Tire liners FTW!

Examining the rest of the tube revealed this situation a few inches anti-spinward of the glass fragment.

Failed tube rubber

Failed tube rubber

There’s a row of holes across the tube, with no corresponding tire or liner damage at all. As nearly as I can tell, the tube rubber simply pulled apart across that line, all at once, and the air went pfft just like you’d expect.

That’s not survivable, but I don’t carry a spare tube (well, two spare tubes: 700x35C rear and 20×1.25 front) on rides around the block. Long bike tours? Yup, spare tires & tubes because I’m that type of guy.

Anyway, I’ve got the tube in hand, so what’s to lose? Scuff it up with the sandpaper and yipes

Tube after scuffing

Tube after scuffing

What’s not obvious in the picture is that all those little spots around the big holes are pinholes. The whole area of the tube must have gotten just barely enough rubber to cover the mold.

I know as well as you do this isn’t going to have a happy outcome, but I slobber on the cement, let it dry, squash on a big patch, install the tube & tire, fire a 16-gram CO2 cartridge into it, and … it doesn’t seal.

The tube is several-many years old, probably from whoever was supplying Nashbar at the time, and it served well, so it gets a pass. I’d rather tubes fail in the garage than on the road and sometimes they do, but that’s not the usual outcome.

My ladies were out gardening at the time and a long wheelbase ‘bent isn’t the sort of thing you can stuff into a friend’s car. Not to mention that my ladies had the magic phone.

So I walked home.

Sometimes a man’s gotta do what a man’s gotta do.

Memo to Self: Schwalbe tube at 8910. Reversed(*) the Marathon’s direction.

(*)They’re directional, but when they get about halfway worn I don’t see that it makes much difference. The rear tire on my bikes wears asymmetrically: probably too many tools in the left underseat bag.

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