RE: [CR]30's Bike Geometries

(Example: Framebuilders:Richard Moon)

Date: Fri, 15 Jun 2007 00:43:02 -0700 (PDT)
From: Donald Gillies <gillies@cs.ubc.ca>
To: classicrendezvous@bikelist.org
Subject: RE: [CR]30's Bike Geometries

For posterity's sake, the golden Legnano has a chromed seat-lug, chromed c-clamp head-lugs and chromed head-tube - with enough space behind the seat tube for a pullman case (about 3"), plus enough space under the downtube for 3 waterbottles. To have some toe overlap one would have to wear a size-27 shoe, at least.

Seriously, though, the bike has what looks like to me maybe a 71 or 70 degree head angle (swag), which means LOTS of trail (see richard jow's 1970's bicycling magazine article on trail).

To summarize that article:

Bikes with more trail tend to go into a straight line, (think shopping cart, where the wheel trails its swivel point) but when you finally wrestle the handlebars into a turn there is more "wheel flop" (think of a chopper motorcycle) as turning the bars doesn't so much rotate the wheel around a perpendicular line coming straight up out of the ground, rather, it rotates the wheel around a line through the hub that is nearly parallel to the ground.

Thus, avocet tires with the raised center ridge can be highly unpredictable (hard to steer back straight again, once turned) on a 1930's bike like this, with lots of wheel flop, since steering straight requires lifting the front end of the bike from the low sidewall back up to the raised center ridge.

- Don Gillies
San Diego, CA