On Sat, Feb 1, 2014 at 10:46 AM, Ashok Kumar S <
s.a...@gmail.com> wrote:
> Yes, you got a point there, I think. But the shop has to convey it that way.
> "It's risky and it might not be safe to fix it and ride. "
A bike shop cannot take that risk. Too many people ignore well-meaning
expert advice even when they do not know better. "Informed choice" is
a misnomer. Comments about medicine and medical doctors in this forum
highlight this. Given the ready availability of forums on Web 2.0
where people can vent without logic or reason or the full facts, it's
a PR nightmare waiting to happen.
I mean, even on this thread, a purely factual question about the
availability of repair shops has degenerated into a discussion of the
motivations and "greed" of software engineers who have taken up
bicycling as a business, their clothing choices, their English accent,
followed by utter economic nonsense on the pricing of services (if
prices are too high in an ostensibly free market, then it is an
entrepreneurial opportunity to seize!).
Now imagine something bad happening despite warnings -- a store may
have to endure posts to groups, facebook, etc. It isn't worth the
cost, in my opinion, especially given that the Internet never forgets.
This is not hypothetical -- I have seen posts condemning manufacturers
where the fault was clearly the riders.
>
> But what if the reason given is that it may break while attempting to true?
It may. It may not.
When my friends and I have tried to retrue aluminium wheels that were
bent, we've sometimes caused the spokes to break through the spoke
hole and ruin the rim (these were cheap rims). We've ruined a number
of rims this way. No rim has shattered or "broken" in our limited
experience.
What might our typical Indian customer do? "You broke the rim when
repairing -- you replace it!" In a fully tensioned standard wheel
with steel spokes, according to Brandt, the spokes are hardly at 1/3rd
yield strength, so it is physically possible to do this. Will our
hypothetical customer understand?
> Also, I know that you know a lot about bike related stuff. I would like to
> learn and know why these experts if they say so, say that aluminium wheels
> must be trashed instead of truing. Do you have any inputs to enlighten me a
> bit?
It isn't true that most aluminium wheels have to be trashed. However,
for most shops, the expertise to evaluate this versus the cost of
being wrong means that they will make the rational economic choice to
trash the rim.
Brandt's the Bicycle Wheel is the definitive guide to understanding
why and how wheels fail and how to repair them. I strongly recommend
reading it. It contains a whole section devoted to repairing wheels as
well as good discussion of how different metals behave.
He mentions, for example, that straightened rims will often have
unequal tension in the spokes and hence may lose trueness over time.
The first part is easily tested using a good tensiometer.
Is a customer willing to live with a wheel that may lose trueness over
time? This is one of the real tradeoffs, not price.
>
> And again, what if the usage is just for regular commute at 20-25kmph
> instead of pace making or racing?
The dynamic stresses on a bicycle are complicated enough that just the
speed of the cycle isn't very meaningful.
Consider a slow-moving cycle that suddenly dips into the standard
Indian pothole (or flies over a speed breaker). What is the magnitude
of the force it is going to experience?
> Thanks and regards,
> Ashok.
>
> Sent from my iPhone
>
> On 01-Feb-2014, at 21:10, Sreepathi Pai <
sre...@gmail.com> wrote:
>
> On Sat, Feb 1, 2014 at 1:26 AM, Ashok Kumar S <
s.a...@gmail.com> wrote:
>
> And I still see it as two wheels
>
> and a very simple gear mechanism. It's the simplest of all the vehicles on
>
> our road.
>
>
> Let's take that example of wheels out of true, lets say due to a crash.
>
> One favorite method of mechanics of old, who dealt with steel wheels,
> is to step on the rim (with spokes removed), and flatten it.
> Sometimes, their favorite all purpose tool, the hammer is also used.
>
> Lets repeat that experiment on an aluminium rim. It is now round, and
> rides "smoothly" and "quietly", as "new".
>
> Would you trust coming down on a hill at 70kmph on it?
>
> I mean, there must be a reason for most respectable bike shops around
> the world to trash aluminium wheels and not "repair" them. Maybe they
> have some PhD metallurgists on staff.
>
> --
> Sreepathi Pai
--
Sreepathi Pai