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From: John B. <slocombjb@gmail.com>
Newsgroups: rec.bicycles.tech
Subject: Re: tech: physics and materials
Date: Fri, 30 Aug 2024 12:27:54 +0700
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On Sun, 25 Aug 2024 20:01:15 +0700, John B. <slocombjb@gmail.com>
wrote:

>On Wed, 21 Aug 2024 13:25:44 -0500, AMuzi <am@yellowjersey.org> wrote:
>
>>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.
>
>Qomafeits? Theru ;look much like tjhe bocycles of my youth. Double
>tpo[ bar stromg enogh top,catryour  buddy sittimhg side saddler.
>Rtneel z'i;e/

Good Lord, where did that come from?
-- 
Cheers,

John B.