Having commuted to work a good bit now on my Schwinn World Voyageur 650B conversion, I like it a lot and would like to do another such conversion, but I need to find a suitable frame to convert. The biggest consideration is BB height. The World Voyageur was really just dumb luck. I bought the bike because it was a really clean example of a model I really liked desipte the fact it might be a bit taller than ideal, hoping the standover height would be manageable, but it was just too tall. By converting from 27 1/4 to 650B I lowered the standover 0.8 to 0.9 inches, which makes it quite comfortable. The problem that can result is the BB height and pedal clearance can become dangerously low, but by luck, the World Voyageur happened to have quite a high BB, so it worked out fine.
Next time I want to be more logical and not need to be lucky. I'll probably use either Rivendell designed Nifty Swifty (33mm) or Grand Bois (32mm) 650B tires, so tire radius will be 324 or 325 mm. A 700C x 23 tire will nominally have a 334 mm radius, so the 650B's will lower the BB about 9 or 10 mm. Ideally, with 170 mm cranks, one would like to keep the BB height not much lower than the 10 1/2 inches, or 267 mm typical of classic road racing frames. A frame with a 10 3/4 inch or 273 mm BB height with 700 x 23 tires would wind up at 263 mm with 32 mm wide 650B's which would be quite acceptable, but one probably doesn't want the BB a lot lower than that.
So anyone know what common classic frames had a BB height of 10 3/4 inchs or more with 700 x 23 tires? I have a 1988 Mercian KOM which I bought as a 54 cm, but forgot that Mercians are measure ctt or maybe even to the top of the seatlug, so ctc it is only about 52 cm. Yet the standover is higher than expected on a 52, more like a 54 ctc frame. Is this high BB typical of Mercian, or perhaps of classic British bikes in general? Any other recommendations of classic bikes with high BB's?
Regards,
Jerry Moos
Big Spring, Texas, USA