From: Todd Kuzma <tullio@theramp.net>
on 7/1/04 12:54 AM, Jeremy Lieberman at jeremylieberman@nyc.rr.com wrote:
> If obviously not
> scientifically proven, none-the-less it would appear that Kirk is on to
> something. I just wonder if his design can yet be further developed, using
> some sophisticated cad programs, which could enable a builder to test
several
> 'bends' of steel seeking the most vertical travel and eventually arrive
upon
> some sort of optimal (or at least the most possible vertical movement with
> solidly connected steel) movement for a given riders weight and road use.
I
> wonder if from a Physics perspective, his long S bend seatstays could be
as
> well done using instead only one long sweeping C bend? Comments? Thanks,
and Todd <tullio@theramp.net> replied: "If you read Mr. Kirk's site, you will see that he is most interested in repeating common bicycle myths rather than science. These effects can be tested, yet nobody does. Why?
There is no advantage to the builder to test. If you come up with a plausible story, people will believe it and will even feel the difference when they ride the bike. Testing can be difficult and expensive. A positive test result just confirms the story. Believers will still believe. Skeptics will likely question the validity and credibility of the test. A negative test result blows the whole concept."
I gotta agree with Todd here, except for the part about testing being expensive and difficult. In this particular case, the goal would be to measure the spring constant of the rear end of the frame. It would be possible to just apply a load to the frame (i.e. put 100 pounds on the saddle), and measure the change in distance from the seatlug to the rear axle. Or, measure the change in vertical height of the seatlug and the rear axle; measure these in the loaded and unloaded state, and use the changes to calculate the compliance of the frame.
As the owner of a Hetchins Vibrant bike (i.e. it has curly stays), I haven't noticed any shock absorbtion going on. There probably is a bit more compliance than bikes with straight stays, but the effect is overwhelmed by the tires. If you really want a smooth ride, I recommend a Brooks Champion Flyer! Those springs deflect quite a bit, making it feel like you are riding with half-flat tires. Very comfy, and still quite classic!
Steve Kurt
Peoria, IL