Re: tech: physics and materials

On 8/21/2024 4:48 PM, Zen Cycle wrote:

On 8/21/2024 8:55 AM, AMuzi wrote:

Our customer wants higher handlebars.  We sold him a new bike and as usual I asked for dimensions from post to handlebar on centers and handlebar to ground from his old bike. That's a tall riding position:
>
http://www.yellowjersey.org/daily.html
>
Since the new model has a carbon steerer, I swapped in an aluminum column carbon blade fork of same dimensions.
>
I reasoned that modern aluminum bars are farther from the stem clamp (stress riser) to the bottom, where climbers pull forcefully, than from the top bearing to the stem. Handlebars are thinner than columns with cold formed curves of various radii while columns are a simple cylinder. Failures in handlebars are rare now (usually precipitated by crash damage, corrosion or both) as are threadless column failures (I have never seen one) so I can't reasonably assess frequency. This was intuitive not calculated.
>
The new wrinkle is that after 50 miles he says another 50mm would be better. Yikes! That's a lot, and the local shop refused to add an extender:
>
https://www.yellowjersey.org/UPSTEM.JPG
>
They also refused to run longer gear cables and brake line if he installed the extender himself.
>
I was OK with the bike as delivered but I'm not so sure about more height. Comments?
>

   Couldn't talk him into a larger frame?

Can't stand over a 61 comfortably and that only adds 2cm anyway.  It's rider style/taste not sizing per se.
--
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971