My 2 cents on the idea of larger diameter tubes for steel frames. When the ratio of wall thickness to diameter for any tube goes above about 50:1 the structure is liable to fail due to "beer canning", any small dent can make it fail quickly. If one were to use larger tubes for steel frame bikes, the wall thickness has to go down in order to keep the weight down. Or, the frame gets heavier. This is one reason why aluminum makes very light frames. The density of the material allows larger tubes with allowable wall thickness to be stiff and light, and because it does not flex much the fatigue life is acceptable. I used to be a proponent for 753 tubing, and built more of these than anyone in the USA I am sure. This only came in French sizes, with the 26mm dia. top tube, and slightly smaller 28mm down tube. I really don't think the small difference in diameter makes that much difference when it comes to head shake. The idea with this very high tensile tubing set was to make the frame a spring. Not very stiff, but nice ride. Ti frames are like this too, but the 753 steel is more alive. I don't think the method of attaching the head tube has much to do with head shake, the lug and butting moves the flexing out from the joint mostly. One other thing that affects head shake has to do with the center of pressure of the front wheel. Some conditions of down hill with side wind will set up a vibration that cannot be controlled. Then if you are cold and shaking, watch out!
Jim Merz Bainbridge Island WA
-----Original Message----- From: classicrendezvous-admin@bikelist.org [mailto:classicrendezvous-admin@bikelist.org] On Behalf Of ΓΈ
Sent: Tuesday, July 09, 2002 1:03 PM To: Classicrendezvous@bikelist.org Subject: [CR]"Mojo" or B. S. Confente/Baylis/Herse
A couple of ideas regarding frame building/construction came together for me in the past few weeks. I had the pleasure of going over the construction of some of the finest framesets ever made ( Masi , Colnago , Herse , Cinelli and Baylis) with Brian Baylis. I discovered a lot of things I should have been looking for all the years that I have been around bicycles. I'm a former racer , mechanic , and now a collector. It's amazing how much that I had been missing all these years . However the real eye opener came when we got to the elements that you can not see until you investigate the construction of the junctions inside the Bottom Bracket shell and head tubes. It is now clear to me that all frame sets are constructed a little differently or with different levels of care for the quality of the finished product. With this new knowledge I am better able to determine if a bikes reputation is based ( "Mojo" , Million Dollar Marketing Campaigns, B. S. , or Real Engineering/Constructor/ Genius )!
There is an interesting article in this months Velo News , which discusses the elements of front end shimmy. Shimmy , head shake , high-speed wobble is caused by top tube rigidity or lack of it. The reason I bring this up is because when we examined the A model Rene Herse frameset it became clear that Herse understood this point well. His frameset was constructed so that the top tube and down tube , in addition to the brazing at the lugs , were also brazed inside the head tube. The French so clearly understood the elements of front end shimmy , that their tube sets also included an oversized top tube. It is also known that Rene Herse built racing bikes with oversized down tubes for extra rigidity , and I believe I saw a Rene Herse Randonneur bike on Ebay last year that also had the oversize down tube treatment . I'm sure there would have been more of oversized tube sets , if builders/constructors did not have to make the lugs themselves to fit the oversized tubes. Bates settled on tubes that were oversized in the center sections only , because he could not get lugs to go with a complete oversize tube set.
I would like to hear from the frame builders/constructors on the list as to what they think of these ideas ( tubes brazed to the head tube; oversized tube sets). This best reason for not brazing the tubes inside the head tube is all the extra work , only Rene Herse and Alex Singer were willing to go the extra mile. Regarding oversized tubes I have a 1995 De Rosa Giro De Italia it has oversized tubes and is one of the best riding bikes in my collection. Would having builders like Baylis and Sachs build bikes with oversized tubes ruin the attempt to capture the past with this type of build? Any comments from others?
Thank you!
Sterling Peters
San Diego