650B conversion questions
MichaelH
with the most experience in this subject.
I had been thinking about converting my '84 Trek 620 frame to 650B,
but had almost shelved the project over concerns that the BB would be
to low, since this frame was originally designed for 27" (630mm
wheels) and I was afraid that even with bigger tires I would loose
about 20 mm of height if I converted to 584. (I'm assuming
((630-584)+10)/2) Then I read a very positive bike review in the
current issue of BQ of a 650B with a bb of 235. Jan Heine said he
didn't experience any pedal strike, except when going over curbs. I
haven't been able to get a good fix on the current frame, which is
hanging up with out any wheels, but would be surprised if it's below
254. I will need to remove the canti studs, so I'd really like to be
pretty sure before I start down the road, or shop floor as the case
may be!
Can anyone shed some personal experience on this?
Thanks,
Michael
franklyn
You should definitely measure BB drop with a set of wheel on first.
Take a pair of 700c or 27" wheels and measure the drop.
I converted a Serotta CRT that had 80mm of BB drop (which means a
fairly low BB) to 650b, with a resultant 248mm BB height with 32mm
Grand Bois Cypres tires on. It was my wife's main bike for a while,
and with 165mm crank arms she almost never struck the pedals.
Franklyn
Jim Cloud
either a 700c or 650B size. Based on my e-mail conversations with Ed
Braley (a frequent internet forum contributor who has a wealth of
experience with 650B conversions), I decided that my bike would not be
very suitable for a 650B conversion, although I'm still considering a
conversion to 700c. One consideration, obviously, is the length of
the crank arm that you're planning to use. You didn't mention the
size of your frame, but generally a frame up to 61 cm would be most
suitable for a "Normal" looking conversion.
Jim Cloud
Tucson, AZ
Steve Palincsar
> I was giving some consideration to converting a 27" frame bicycle to
> either a 700c or 650B size. Based on my e-mail conversations with Ed
> Braley (a frequent internet forum contributor who has a wealth of
> experience with 650B conversions), I decided that my bike would not be
> very suitable for a 650B conversion, although I'm still considering a
> conversion to 700c. One consideration, obviously, is the length of
> the crank arm that you're planning to use. You didn't mention the
> size of your frame, but generally a frame up to 61 cm would be most
> suitable for a "Normal" looking conversion.
You'll get a bit more bottom bracket drop switching 630 to 584 than
switching 622: 4mm more if all else remains the same.
You'll also need 4mm more brake reach. Those 4mm are often
insignificant switching from 630 to 622, but since some brakes barely
have enough reach for the 622->584 conversion, the extra may be a few mm
too far.
Crank length can be an issue. On your side, though, back when 630 was
the common tire size, 170mm was the common crank length, whereas today
it's considered short by many.
Bryan @ Renaissance Bicycles
grantpetersen.mp3) that a 700x23c wheel + tire is roughly equivalent
in diameter to a 650Bx38c wheel + tire. So if you can measure your BB
drop with a "normal" wheelset, this should give a pretty good idea of
the predicted BB drop.
And from experience, I would leave the Canti mounts in place until you
actually get the 650B rims test fitted to the bike ... just in case
(for whatever unforeseen reason) Calipers don't work, you have a
backup plan.
ATMO, any bike is a good candidate for a "fun" conversion. Assuming
this is not your primary bike, there is no harm in putting a
worthwhile bike back into service and learning a few things along the
way. And if it is your main ride, do it anyway.
Good luck and Happy Holidays,
Bryan