RE: [CR] Group Physics here stinks! (on topic)

(Example: Component Manufacturers:Avocet)

Date: Mon, 3 Jun 2002 09:43:50 -0700 (PDT)
From: "Tom Dalton" <tom_s_dalton@yahoo.com>
Subject: RE: [CR] Group Physics here stinks! (on topic)
To: classicrendezvous@bikelist.org
In-Reply-To: <3.0.32.20020603091214.00713c84@pop.tiac.net>


Hey Michael- The hysteresis losses from the frame are truly small, as you've been saying all along, and as your friend confirmed. I would argue that it is the effects of flexure on the biomechanical interface between the rider and the bike that make flexible frames a liability, performance-wise. As you said, there is a right amount of flex, and less is not always better, but too much is too much also and at some point frame flex can slow you down, even if the tubes are only shedding a tiny amount of energy as heat. The whole entropy thing really comes into play when you look at the termal losses from the rider himself. Most of the work a rider does is put toward moving air (displacing about one-half ton per minute at 25mph) and a much smaller amount goes to frictional losses in the tires and drivetrain (and in the frame too!). The amazing part is how much of the energy that a rider expends goes not into doing work (moving air, heating up frame tubes, whatever) but is lost as heat. The rider's body sheds an enormous proprtion of its energy as heat, about 80% I think. It leaves in liquid and vapor coming off his skin, mostly. It is normal for heat engines to have losses like this, and the human body is actually much more thermally efficient than an internal combustion engine. far more than 80% of the energy from gasoline is exhasted or radiated away. There is a very interesting segment in a book called "The Ring of Truth" by Phillip Morrison that deals with entropy in heat engines, conservation of energy, and the equivilency of matter and energy. It uses Td'F racing cyclists as the engines and standard jelly donut units (JDs) as the measure of energy. Tom Dalton Bethlehem, PA

Michael Kone <bikevint@tiac.net> wrote: Hey CR folks - I'm getting a lot flack on the entropy argument for frame flex - people essentially arguing that frame flex leads to lost energy so flex is significant.

I just went riding with my engineering/physicist friend that works at NIST (National Institute of Standards - the research facility that had a Nobel Prize winner last year) and he was incredulous when I told him what folks have been e-mailing to me. He said of COURSE there is ENTROPY - but it is less than one percent and perhaps closer to one tenth of a percent. The key is that the entropy energy loss is INSIGNIFICANT to the benefits of having SOME flex in a frame. This is why, for years, every engineer I've met has been quick to point out that frames DON'T to a SIGNIFICANT extent abosorb energy.

Why does all this matter? Why is it on topic? Because one of the main - if not the main - drawing card of steel frames is the sweet ride they provide. If people are numb to the ride and the fun feel of a great frame, than at some point why not ride a stiff aluminum frame with a carbon fork and call it a day. If framebuilders ever loose sight of ability to tune the ride in steel for a wonderful pleassurable ride than I'm afraid the future of great steel bikes is rather dim.

Mike Kone in Boulder CO _______________________________________________

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