At 9:27 PM -0700 10/22/08, EPL wrote:
>In looking at 531 frames with "old" Continental Oval fork
>blades (i.e. before Reynolds offered blades profiled more like
>Columbis blades), I note that the rake bend is mostly low on the
>blade, with much of the upper blade straight.
The "Imperial Oval" was the older one. The "Continental Oval" is the
Columbus shape.
>
>With the later New Continental profile (like Columbus), rake bends
>may start much higher, even more than halfway up. Best proponent of
>this gentle gradual bend is Ron Cooper, IMHO.
>
>Is this change in style a simple function of taste, or was the old
>oval blade profile hard to bend higher up vs. the more slender
>Columbus-type oval profile?
It's mostly a matter of taste, but of course, it's a lot harder to put a small-radius bend into the bottom of the blade than a gradual bend into the entire blade. For the small-radius bend, you also need a blade that is relatively small in diameter and has a decent wall thickness, otherwise, the blade may ripple.
Bicycle Quarterly's tests have confirmed what most builders knew all along: The shape of the bend matters for shock absorption. The older, small-radius bend absorbs shocks better, because the angle between the blade near the dropout and the road shock is greater. In extreme cases, the blades are almost horizontal at the bottom, and thus easy to flex up and down. The worst scenario are straight blades, which compress under road shocks, rather than deflect. And you can't compress a fork blade much!
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com