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From: "Charles T. Young" <youngc@netreach.net>To: <classicrendezvous@bikelist.org>

Subject: Re: [CR]Re: Reducing the "Polar Moment of Inertia"

Date: Sat, 21 Apr 2001 08:01:49 -0400

I recall once having seen a statement that removing a gram of weight from the wheel (not specified whether from the rim/hub/other) was the equivalent of removing 2.3 grams from the frame (or other non-rotational components). Anybody recall that tidbit? Seems a little to "precise" a value to have arisen from a guess.

Charlie Young Honeybrook, PA

-----Original Message----- From: RMAugust@aol.com <RMAugust@aol.com> To: classicrendezvous@bikelist.org <classicrendezvous@bikelist.org> Date: Friday, April 20, 2001 6:56 PM Subject: [CR]Re: Reducing the "Polar Moment of Inertia"

<< Why doesn't someone offer some proof that weight matters all that much to begin with and that rim and tire weight matters more. All I see are unsubstantiated claims. I say until some one can prove different rotating weight doesn't matter more, and that weight in general doesn't matter all that much. >> Given two wheels of equal weight, one with a greater proportion of its weight in its rim and tire will have a greater polar moment of inertia which therefore will accelerate at a slower rate of speed. A good example of this is an ice skater rotating with arms extended (high polar moment) and then moving the arms in very close to the body (lower polar moment). The result is that the speed of rotation increases dramatically.

Wind resistance plays a small role in this but mainly it's the reduction of the polar moment. In the case of wheels, reducing the polar moment makes a bike feel more fleet and in competition can give one an actual speed advantage off the line. That's the proof of why reducing rim and tire weight matters more than reducing weight in general.

As to reducing weight in general, I think it's generally known that, given no other variables, a lighter bike will be more efficient to move owing to fact that less calories are required to fuel it.

Randy

Corral De Tierra, Ca.