I thought Dave actually presented two examples, one illustrating zero trail and one which calcs out to 40 to 45 mm trail, depending what radius you assume. I didn't think he generalized either of those data points to "all bikes." Besides, the 40 mm case is the one flagged as a problem, Jan, not the 0 mm case. I agree, if I believed he meant to say "all bikes of a certain period had zero mm trail," I would see that as a problem. Likewise, a 40 mm generalization.
Similarly, I assume you aren't saying "no bikes of that same certain period had 40 mm trail."
On Sun, Oct 11, 2009 at 11:40 AM, Jan Heine <heine94@earthlink.net> wrote:
> 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
>
--
Ken Freeman
Ann Arbor, MI USA