Yikes! Disaster struck the Fury RoadMaster! Those interested
in technical questions should skip to the end for a picture
and a question.
Wheeling it away from where it sleeps with one pedal up on a
wooden picnic bench, I heard an odd sound.
Rolling it back and forth revealed that the sound came from
the rear wheel at one particular point.
Brakes? No, the pads weren't touching the rim.
Tire rubbing against the frame? No, there was room for a big
rat to crawl through between the tire and the chain stays or
seat stays when the noise was heard.
Something caught in the plastic spoke protector? No, it spun
freely.
A mechanical disaster inside the freewheel or--
Oh. I see. The massively treaded rear tire is almost flat.
The noise comes when a section of the bead that's almost
loose rolls under the hub and gets squeezed back against the
rim.
The Fury is flipped onto its back with its thumb-shifters
and speedometer held off the back porch concrete by a wooden
2x4 frame (nothing is too good for a high-quality bicycle).
An adjustable wrench loosens the axle nuts, and out comes
the rear wheel.
Hmmm . . . a bit heavier than my touring bike's wheel.
A thumbnail depresses the Schrader valve enough to let the
rest of the air out and the monster tire comes off the rim
quite easily.
Odd, nothing stuck in the tire, rim strip in place, no
apparent hole in the tire. It's almost sunset, so to hell
with it for now.
One of three spare 2x26 tubes bought on sale goes in and the
tire goes back on the rim almost as easily as it came off.
After a brief introduction to Mr. Air Compressor, the tire
seats nicely and--
D'oh! When inflated, gargantuan treaded tires do not slip
past the brake pads. Thumbnail adjustment of the air
pressure eventually reduces the stiff and swollen tire
enough for its return to its rightful place, followed by
another CPR session with the air compressor.
After an uneventful ride, the suspect tube is placed in the
dunking stool of the kitchen sink and quickly found guilty.
A tiny stream of bubbles leaks out from underneath an odd
gash--a flap, really--on the edge of the circle where the
valve stem attaches to the tube.
The tire went flat overnight after over 160 four-mile rides,
so whatever created the tiny flap happened yesterday, but
the rim strip was in place.
Closer examination shows that the rubber seems to have
split, bursting from the inside and peeling up a tiny flap
roughly over one spoke hole next to the valve.
Viewed in profile, little bulges appear on either side of
the inner tube's valve stem. Further away, around the inside
of the tube, are a few more odd bulges.
They seem to be centered over the spoke heads, with a dent
in the tube where it sat on the spoke head and a bulge on
either side. Here's a picture of the clearest example:
http://home.comcast.net/~carlfogel/download/tubebump.jpg
The spoke head was under the "in" of "Shin" and the shiny
bumps on either side are protruding. Most of these marks
amount to little more than scuff marks.
Why are there raised bumps on either side of the inner tube
where it sits on the spoke head? Why does the rubber distort
like this?
Carl Fogel