gpvb1@comcast.net wrote:
>Date: Thu, 29 Sep 2005 00:15:07 -0400
>From: Marcus Coles <marcoles@ody.ca>
>To: classicrendezvous@bikelist.org
>Subject: Re: [CR]Frame Flex Testing
>
>At 6' and 200lbs with a non-typical cyclist physique I find significant lateral frame flex at the bottom bracket unacceptable, by significant I'm talking auto shifting and the big ring rattling both sides of the front derailleur cage.
>While this may not consume power and cause the bottom bracket shell to glow red it is quite an annoyance.
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>That is why you need tubing gauge to be rider-appropriate (since the diameters didn't vary in the "old days"). If you check the tubing manufacturers' specifications, there was frequently a recommended max. rider weight associated with each type of tubing (often widely ignored, unfortunately). For Columbus SL, it is 150 pounds. For SP, it is 200 pounds. For KL, it's 125! You are at the upper limit for SP....
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I am sadly aware of this situation and have a history of broken frames
from what I believe were mostly fatigue failures in and around the BB.
I select bikes with this in mind and avoid becoming the caretaker of
valuable frames made from unsuitable tubesets no matter how appealing.
>As for frame flex improving the ride, now IMHO that's snake oil. A bike frame is pretty much a truss vertically and deflection is minimal at best. Tires, inflation pressure, wheelbase, headtube angle, where you sit and where your hands are, make the difference for ride feel.
>I'd bet that the Raleigh 3 speed used as an example of stiffness earlier seems "dead" because of the sixty something degree frame angles, the four foot wheelbase and the 35+lb weight.
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>Uh, a frame's vertical compliance doesn't matter in your opinion? Ever ride of of them early Cannondale things? They will pound you into a pulp, IMO, over long distances. Way too stiff vertically.
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Only once I can't recall the model and I found it a novelty at the time,
the ride OK on smooth roads, it had steel a fork BTW and I only rode it
for about 20 miles hardly enough to form an opinion.
I agree with the observation that different bikes ride differently. I just can't get my head around it being the vertical compliance of the main or rear triangle that makes the difference. There are so many more components which exhibit observable deflection under verical load on a bicycle it becomes a "Princess and the Pea" thing as far as I am concerned and I am quite obviously not worthy of the title. ;-)
Marcus Coles
London, Ontario, Canada.