Well as I was speculating yesterday, perhaps avoiding overlap was yet another advantage of 650B wheels on the old French touring bikes. In the case of touring bikes, the overlap arises due to the use of fat tires and mudguards, rather than a short wheelbase. Many of the French touring bikes had 40mm or wider tires, so when you add mudguards to that, you don't need a terribly short toptube to get overlap with 700C wheels. But 650B of course gives a lot more clearance. I doubt this played a part in the original development of 650B tires, since early in the 20th century bikes had very long fork rack to absorb shock on rough roads, which pretty well prevented any overlap. But as roads got better and fork rack got shorter, this may have become an issue in design of touring bikes, some of which were using 700C wheels by WWII. It would be interesting to know if there was any discussion in the French cycletouring press in say the late 30's through the 50's of the issue of toeclip overlap and how it affected the choice of 650B versus 700C wheels.
Regards,
Jerry Moos
Big Spring, Texas, USA
> From: Marcus Coles <marcoles@ody.ca>
\r?\n> Subject: Re: [CR] Track bike set up
\r?\n> To: "CLASSIC RENDEZVOUS" <classicrendezvous@bikelist.org>
\r?\n> Date: Monday, March 9, 2009, 11:07 PM
\r?\n> I just checked my only track bike a 57cm 1981 Bianchi Pista,
\r?\n> with a medium ALE toe clip on the Gippemme pedal and 21mm
\r?\n> tire it misses overlapping by a coarse hair. I think the
\r?\n> wheelbase is in the 98cm range and the head angle ~75
\r?\n> degrees with about 30mm of fork offset.
\r?\n> I'm no frame designer, but smaller frames definitely
\r?\n> run into the overlap problem more easily and the ways around
\r?\n> it are compromises. More fork offset ("rake"),
\r?\n> slacker head tube angles, longer front center with the
\r?\n> necessary steep seat tube to keep reach within reason.
\r?\n> I'm sure there are some more that I've missed.
\r?\n>
\r?\n> To me the most obvious solution and it seems the most often
\r?\n> avoided is to use smaller wheels such as 650c or perhaps
\r?\n> even 24" for smaller racing frames.
\r?\n>
\r?\n> Marcus Coles
\r?\n> London, Ontario, Canada