[CR]The Modern Hetchins?

Example: Framebuilders:Rene Herse

From: "Jeremy Lieberman" <jeremylieberman@nyc.rr.com>
To: <classicrendezvous@bikelist.org>
Date: Thu, 1 Jul 2004 01:54:49 -0400
Subject: [CR]The Modern Hetchins?

Looks like there's a new generation Hetchins being built. I recently discovered the work of Montana framebuilder David Kirk- ex Serotta builder/designer of Serotta's DKS-aka D. Kirk, elastomer/piviting suspension- and was quickly reminded of Hetchins. From most accounts that I have read, the DKS system apparently works quite well- obviously not like a spring/damper, but providing enough travel for most on-road uses.

Anyhow, to cut to the chase, Kirk left Serotta, Serotta kept the patent for themselves, and Kirk set up shop on his own. Kirk has now come up with a way around the patent by re-interpreting the Hetchins style curve (like a large steel leaf spring), only it seems he has done it rather differently than anyone before him, including Hetchins. See an example here...


It seems as if Kirk has done the reverse of Hetchins, seeking to gain added suspension effect not from the chainstays- as was Hetchins specialty (though I understand that Hetchins did put some slight bend in his seatstays), but instead from the seatstays. It could be that Kirk has created a more effective design than Hetchins, in that (as some have remarked) the seat stays play a larger role in suspending a bike in the vertical plane than chainstays do- and therefore will contribute a larger movement up and down than chainstays will.

I'll note that I have read several ride reports on the Serotta forum that describe the ride as more comfortable than any number of X bikes etc. Of special note was a forum member who directly compared his Kirk bike with both a traditional rear triangle and with a newly retrofitted "Terraplane" triangle, and who believes it makes a marked difference. 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,
Jeremy Lieberman
New York City