From: jobst.brandt@stanfordalumni.org
Subject: Re: switching tire sizes...
Newsgroups: rec.bicycles.tech
Message-ID: <vww0a.64415$Ik.2628417@typhoon.sonic.net>
Date: Thu, 06 Feb 2003 17:00:11 GMT

A Muzi <am@yellowjersey.org> writes:

>>> My trainer seems to be eating my good road tire and the only spare
>>> I have at the moment is of the larger size. And yes I have light
>>> pressure on the tire while it is in the trainer. Maybe I should
>>> ditch the trainer for a better one??

>> I don't use the trainer but my wife does.  I've got a very beat
>> rear wheel with a $10 tire on it.  The reason that I change the
>> whole wheel is that I believe that holding the wheel by the ends of
>> the axel and rocking side to side puts strain on a wheel.

> What sort of strain?

> Could you compare/contrast with actual road impacts?

> I hear that comment a lot lately but so far never a good
> explanation.  It usually starts with, "I heard that trainers are
> bad for bikes".  As someone who regularly aligns forks that have run
> headlong in to immobile objects and who straightens/replaces rims
> that have been bashed, I have yet to see similar impacts from
> trainers!!

I think this is a case of missing cause and effect.  Trainers with
less than about 8" diameter rollers can damage tires and this is often
misattributed to various unrelated effects.  Flexing a tire at a
continuous high rate causes internal heating and tread delamination
ala Ford Explorer.  Considering the length and curvature of the
contact patch should make apparent how severe tire casing flex is.  I
recall tubular tires coming apart while riding small diameter rollers
along with all the conjecture about the cause.  This does not affect
wheels nearly as much, load distribution from the tire being broader.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA