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From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: tech: physics and materials
Date: Wed, 21 Aug 2024 13:25:44 -0500
Organization: Yellow Jersey, Ltd.
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On 8/21/2024 1:12 PM, Frank Krygowski wrote:
> On 8/21/2024 11:05 AM, AMuzi wrote:
>> On 8/21/2024 9:07 AM, John B. wrote:
>>> On Wed, 21 Aug 2024 07:55:51 -0500, AMuzi 
>>> <am@yellowjersey.org> 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?
>>>
>>> If I was in business and a similar question came up I 
>>> believe I would
>>> contact the manufacturer or U.S. Distributor.
>>
>> I did, naturally.
>> Carbon steerers warn about maximum stem height over top 
>> bearing (and reasonably so IMHO) but there aren't firm 
>> limits for metal columns.
> 
> That's a very tall setup, all right. I think the bike is 
> severely undersized for the rider, and a much bigger frame 
> would be the real solution. I'd be very wary of going any 
> higher - not that I have your experience viewing failures.
> 
> This phrasing confused me: "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."
> 
> But loads applied in bicycling are largely unknown and vary 
> tremendously with the individual, which makes any attempt at 
> calculations impossible. Will this guy really be pulling on 
> the bars while doing steep climbs?
> 
> Vaguely related: Our Bike Friday New World Tourists
> https://www.flickr.com/photos/16972296@N08/7410976626/in/dateposted-public/   have extremely tall gooseneck stems, made of steel. Mine flexes disconcertingly when I pull on the bars while climbing. I'm told it's also tough on the headset.
> 

Yes, many unknowns and that's why my decision was intuitive, 
not calculated.

He can't stand over a 61. This is a 59. It's not a frame 
size problem so much as a customer who wants to ride a race 
bike like an omafeits.
-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971