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 650B wheeled bicycles
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Why?
I suppose the big question is: Why would someone want to
take a bike that was designed for one wheel size and convert it to use
another? Some answers:
- You want a softer ride than you can get from any tires that your frame was designed to accomodate.
- You want fender/mudguard clearance on a bike that wasn't designed for it.
- You like the slightly more substantial looks of the wider tires typical to 650b wheels.
- You want to be different.
- You want the bike to handle differently.
- You want to be able to do some light off-road riding but aren't
comfortable doing it with the tires that your frame was designed to
accomodate.
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Will your bike work?
Maybe. Certainly not all 700c bikes are ripe for conversion to 650B. Some things to keep in mind:
- You'll probably be dropping the bottom bracket. If you use
long cranks, your bike has quite a lot of drop to begin with - say
7.5cm or more, and/or you are planning to use small cross section 650B
tires you'll want to check this one out very thoroughly or make sure
you don't pedal through corners. Various of the 650B tires
currently available seem to have radii between 325mm and 334mm.
If you're moving from small section 700c tires, which may have a radius
of only 335mm to a wide 650B with a radius of 332mm then your bottom
bracket shouldn't be noticeably lower after the conversion. If
you're trying to convert a Rivendell with an 8cm drop and are planning
to use 325mm radius tires you'll be looking at a bottom bracket height
of only about 9 1/2" - which is very low for anything longer than
probably 155mm cranks.
- You'll
be increasing the distance from the brake centerbolt to
the rim surface by about 19mm. This will thow out cantilever
equipped 700c bikes unless you're willing to get the cantilever studs
moved by a framebuilder (necessitating a repaint.) If your bike
uses short reach brakes (i.e. 39mm-49mm) it should be relatively easy
to find brakes
that will work with the additional reach - some sidepulls but mostly
centerpulls. If your bike currently uses long reach brakes (i.e.
47mm-57mm) you may have more
difficulty.
- There
might be problems clearing the chainstays with wide 650B
tires. If your chainstays aren't dimpled and they run fairly
close to the rims on your current wheels you might not be able to fit
the wider section 650B tires even though the wider portion of the tire
will be nearer then hub than with 700c tires. A quick rule of
thumb would be at 320mm from the axle you'll need 42mm of clearance for
Col de la Vie tires.
- You may be changing the handling quite a bit. If you are
moving from moderately wide 700c tires to moderately wide 650B tires
you stand to drop the bottom bracket maybe 15mm or more and shorten the
trail by as much as 4mm. These numbers don't sound impressive but
remember that they might be between 6% and 9% of their associated
values. Changes of this magnitude can seem pretty dramatic to
some individuals, while others might not even notice them.
Whether the changes are for the better will depend upon the user,
though I haven't heard of any complaints about the modified handling
yet.
Some important numbers to keep in mind when considering a conversion:
- 295mm This is the approximate distance from the center of the axle to center of the rim on 650b wheels.
- 371mm Approximate maximum distance from the brake centerbolt to the axle to allow for use of 750mm centerpull brakes.
- 320mm Approximate distance of the widest portion of a 650b tire from the axle.
- 650mm Approximate diameter of the smallest readily available 650b tire (Michelin).
- 675mm Approximate diameter of the popular Panaracer 650b tires.
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Some frames that have been successfully converted
- Heron Road (not the current Heron Rally, though that might work with longer reach brakes.)
- Waterford era Rivendell Road
- Lotus Legend
- Fuji Team
- Bianchi Limited
- Raleigh Super Course
- Univega Gran Rally
- 1986 Meral
- 1985 Centurion Super Le Mans
- Mercian Colorado
- Surly Pacer
- Miyata 712 from the mid/late 80's
- Jeff
Lyon frame designed for long reach (47/57mm) brakes. Update -
This bike has been taken back to 700c as the owner prefered the
handling characteristics with the larger wheels.
- Quickbeam
- Trek 400
- Rivendell AllRounder (converted from 26" to 650B)
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List of bikes that won't work for conversion or have serious caveats
- Vitus 979. The chainstays do not have enough separation for
Col de la Vies, though they'd likely work well with the Michelin
Megamium.
- 1999-2000 Scwinn Paramount. The chainstays do not have
enough separation for Col de la Vies, though they'd likely work well
with the Michelin Megamium.
- 1990
Masi Gran Criterium. Not enough space at the stays for Col de la
Vies, just enough for Megamiums. Douglas Brooks has reported that
the end result is not aesthetically pleasing.
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Acknowledgements
I would like to thank the people who have gotten others thinking about
the 650B conversion. Olof Stroh may be said to have started the
ball rolling on the Internet BOB email list when he mentioned having
done more than one of these conversions (650B is a common size in
Sweden where he lives) in the past and liking the results. Rory
Cameron proceeded to convert a Univega sport touring bike and, this is
the important part, he documented the conversion in Rivendell Reader 33
- for which also thanks to Grant Petersen for publishing the
article. From there Ed Braley started rapidly converting some of
his stable - most of which are written up below. Other members of
IBOB took a bit more time with their conversions but they are getting
there!
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