On 4/14/2010 1:54 PM SMS wrote:

On 14/04/10 9:30 AM, raging raven wrote:
So what causes the tube to rotate inside a clincher tire? Under-
inflation? I frequently service a friends bicycle and every time the
tubes have moved until the valve stem is skewed at a significant
angle. Schraeder valves/26x1.95 city bike tires if that makes any
difference. Thanks in advance.

There's a tendency to use cheap tubes that cover too wide a range of
tire sizes. These tubes are too small for the larger tire sizes of the
range specified on the box. When inflated, the rubber is stretched and
there is insufficient friction between the tube and the outside of the
tire, or the tube and the rim tape/strip.

I've seen 18-28mm tubes from one manufacturer while a competing
manufacturer will have an 18-23mm, a 23-28mm, and a 25-32mm. Always
choose the largest size possible. Never use a tube with more than a 7mm
range from smallest to largest, with a tire at the large end of the range.

If you're buying tubes at Wal-Mart or Target, they have limited sizes.

In Presta, Performance has 700c x 19-26, 700c x 28-32, 700c x 35-38,
700c x 48-52.

What? Are you trying to say that the tube cannot stretch enough to press
firmly enough against the inside of the casing and the rim to avoid
slithering about, while at the same time it manages to provide enough
internal pressure to keep the tire sufficiently inflated and the rims off
the pavement?

On the face of it, that seems a stretch (heh).

I'm not saying you're wrong, I'm saying I don't see it.

--
Mike "Rocket J Squirrel"
Bend, Oregon