Re: [CR]30's Bike Geometries


In-Reply-To: <700376.60114.qm@web82206.mail.mud.yahoo.com>
References: <700376.60114.qm@web82206.mail.mud.yahoo.com>
Date: Fri, 15 Jun 2007 15:30:45 -0700
To: Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net>, Mitchell Gass <mitchell@gassworks.com>, classicrendezvous@bikelist.org
From: Jan Heine <heine94@earthlink.net>
Subject: Re: [CR]30's Bike Geometries


At 2:35 PM -0700 6/15/07, Jerome & Elizabeth Moos wrote:
>Were Pre-War bikes really super-long trail?

Here are a few examples:

1920s: Alcyon Tour de France model (top of the line): 66 degree head angle, 80 mm fork offset, trail ca. 68 mm, flop factor 25.3 mm

1939: Oscar Egg (see Bicycle Quarterly Vol. 4, No. 3): 71 degree head angle, 45 mm fork offset, trail ca. 70 mm, flop factor: 21.5 mm

1949 Bartali of Gino Bartali (his actual bike): 71.5 degree head angle, 55 mm fork offset, trail ca. 57 mm, flop factor: 17.2 mm

1948 Bianchi of Fausto Coppi (his actual bike): 73 degree head angle, 70 mm fork offset, trail ca. 32 mm, flop factor: 8.9 mm

1950s Bianco racing bike (Bianco built the frames for many French racers): 73 degree head angle, 56 mm offset, trail ca. 47 mm, flop factor 13.1 mm

You can see the transition from shallow head angles and lots of trail to steeper head angles. You see some experimentation (Coppi's and Bartali's bikes are quite different!), but then builders standardize on a moderate trail geometry. When you look at various bikes featured in BQ and measured by Chuck Schmidt, you see that the Bianco is pretty much what remained standard racing geometry for a decade or more.

The bikes above are just a few examples of bikes I've measured. They are typical for bikes of their era.
> If I understand the concept correctly, shallow head angles does
>increase trail. But doesn't a long fork rake decrease trail?
>Pre-war bikes typically had long fork rake as well. So was the net
>result really that drastically different from modern bikes with
>steeper head angle, but also less fork rake?

The wheel flop is drastically different - see the flop factors above. Unfortunately, I haven't put in enough miles on 1920s and 1930s bikes to comment on their handling.

--
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com