At 6:12 AM -0400 10/11/09, Ken Freeman wrote:
> Interesting, only problem is that the picture he uses shows a bike with
> around 40mm of trail (T=14% x Rwheel according to autocad)
>Why is that a problem? It's not common today, but so what?
The problem is that Dave Moulton wrote that the bikes back then had zero trail, when in fact they didn't.
I have measured enough bikes from all eras for our book "The Competition Bicycle - A Photographic History" to say with confidence that every bike I have seen had a positive trail number. In fact, in the 1930s, many bikes seems to have rather long trail figures of 60+ mm, while other had shorter trail, because some builders steepened the head angles earlier than others. Only by the 1950s did racing bikes in Europe almost universally adopt shorter trail figures of about 30-50 mm.
Dave Moulton also writes that bikes in the 1930s had a wheelbase that was 10 to 13 cm longer than today. That may have been the case in the 1920s, but by the 1930s - the period Dave talks about - wheelbases were shorter, on the order of 1050 mm, or about 6-8 cm longer than today.
Dave Moulton's assertion that bikes of the 1930s - 1950s didn't handle well doesn't match my experience. Of course, he specifically talks about small frames... which I don't ride.
As I have pointed out in Bicycle Quarterly, the old professional-level bikes (and Dave appears to talk mostly of mid-range British production bikes, which may have been very different) were highly adapted to the type of racing of the time. Wider tires and longer stage required different geometries. As tires got narrower and stages shorter, the geometries adapted to suit.
73 degree head angles on racing bikes have been documented as early as 1949 on Fausto Coppi's Bianchi (many cyclotouring bikes had these head angles in the 1930s), combined with a very long fork rake of 70 mm. The bike must have worked OK, as Coppi won the Tour de France on it. By the mid-1950s, you see what I'd consider the optimal geometry for 28 mm wide tires - 73 head angle with about 50-55 mm fork offset - quite commonly. From there, the fork offset decreased simply because narrower tires require more trail to be stable, as they have less pneumatic trail.
Jan Heine
Editor
Bicycle Quarterly
2116 Western Ave.
Seattle WA 98121
http://www.vintagebicyclepress.com