before this gets too far along, why not keep the discussion easy and define twin-plate; is it the type made by using 2 seperate pieces? the type that simply "suggests" twin-plate by virtue of its visual appearance? other? e-RICHIE chester, ct where twins are not over-rated...
Jan Heine commented and speculated about these crowns. Please indulge me to convert this to a bit of virtual dialogue:
JH: Indeed, most bikes in the French technical trials had twin-plate crowns, even if the makers usually did not use them on customer's bikes.
JH: One question I have is how well these crowns can deal with twisting of the fork blades from brazed-on brake pivots - canti or even more pronounced with centerpulls, where the pivot is brazed close to the crown, with little blade to "absorb" the flexing motion each time the brake is applied. Obviously, this twisting action would stress the lower plate more than the upper one and might lead to failure. Thoughts? HS: Jan, I think you protest too much about the matter. Empirically, they seem to do just fine, so the stresses must be manageable. Indeed, has anyone heard hints to toe-in brake pads differently for these crowns?
JH: I wonder whether this is the reason most French constructeurs did not use twin-plate crowns on their production bikes after World War II. In the 1930s, they were found on many bikes, including tandems. The fact that they switched from a lighter to a heavier crown on their production bikes can't have been cost, so there must have been a functional issue. HS: I don't quite follow your logic. Most (but not all) the less expensive post-war French production tandems (particularly Gitane and Follis)I've seen had twin-plate crowns. My guess is that they were less expensive in low volumes for the oversized tubing used on the tandem forks. At least in pre-CNC days, I've had the strong sense that stamping was much less expensive than machining - but only if many, many pieces were to be made from the same dies. My own guess, totally unsubstantiated, is that this change reflects style and fads, much like center-pull preference giving way to side-pull preference in the 70s, and then to dual pivot. All of 'em stop the bike, even if each has a somewhat different feel. But, at some point, twin plate crowns were just unbearably old-fashioned (witness Masi?) thanks
Harvey "to speculate is to live" sachs mcLean va.
-- Jan Heine, Seattle Editor/Publisher Vintage Bicycle Quarterly c/o Il
Vecchio Bicycles 140 Lakeside Ave, Ste. C Seattle WA 98122
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