Good candidate for 650B conversion?
 

i recently picked up a nice japanese touring frame in my perfect size (24.5" c-t). it was originally built with canti bosses for 27" wheels. the frame is going to be sent for powder coating because it is currently in rough shape. since i'm not concerned about the original paint, i'm also curious if it would make a good candidate for 650B conversion by repositioning the canti bosses, so that i can get some nice 650B fatties on there. that brings up four issues as far as i can tell:

1) canti repositioning: can this be done at reasonable cost? will doing so weaken the fork?

2) bottom bracket height: the drop is 63mm. that's a fairly high bottom bracket, no? and that's good for 650B, right?

3) tire clearance / tire choices: since the fattest part of a 650B tire would be approximately 320mm from the axle center, i measured the clearance that far from the front and rear dropouts and came up with 46mm between the chainstays and 45mm between the fork blades. while that would probably exclude using 41mm hetres with fenders (unless the fenders were modified), what other decent 650B tires options exist in the 35-40mm range?

4) appearance: how would 650B look on such a large frame? would it look "off"? can anyone post pictures of their large-frame 650B conversions?

I don't suppose there's any chance you could mount the arms from a pair of centerpull brakes on the same studs, and call them U brakes?

I doubt anyone would notice! We're all used to seeing the usual wheel sizes in a wide range of frame sizes, so the proportions vary just as much and it still all looks "normal" to us. Aside from that, 650b rims are smaller but they typically take fatter tires, so the wheels don't end up looking smaller at all.

Below is not what you asked for, but here (again) is my 62 cm Lambert frame with 26" wheels (559 ISO) and 140 mm cranks. I should have let you ride this, you'd be amazed how comfortable it is.

http://farm5.static.flickr.com/4029/...cb20c9e1_b.jpg

Anton, I could probably send you in the right direction for the re-positioning the canti's at a very reasonable cost ..

Scott

What do you guys use for powdercoating in the area? Do they sandblast? Cost?

Anton, how are you measuring? The number that I use is that the height from the center of the BB to the ground should be no less than 10"/25.4cm. You can get away with a bit less, but risk pedal strike.

The new Pacenti PariMotos measure about 38mm and are very nice. I've also ridden the Col De la vie quite a bit, and they also measure about 38mm. Some find the tread too "squirmy," but it didn't bother me. I also run Nifty Swifty tires on my porteur; those measure about 35mm, and I've been very pleased with their performance.

Neal

stien, there are several inexpensive powder options in the area that i know of: long beach custom fab in plymouth, and sugar coat in allston.

scott-- cool! PM sent.

i didn't have the time to do an accurate ground to BB measurement since i don't have an even floor and i'd have to do a wheel mockup on the frame. i strung a string tautly between the F/R dropouts with the fork centered, with the string centered at the height of the axle center. then i measured the vertical distance from the string to the BB center. i thought this is what is referred to as BB drop?

Soma Fab is also selling a 650bx38mm tire with the Pasella tread.

That's a beautiful Lambert, RHM! Are those 1.5" Paselas?

Thanks! 1.5" Paselas, yes, I think so.

I'm likely confusing terms, but here are guidelines on "Bottom Bracket Height" for 650B conversions that I find helpful:

http://www.bikeman.com/content/view/1161/33/

Neal

Thanks for the info!

great source of info, neal. it seems that either BB drop or BB height describes the height of the BB, just relative to two different things (BB height being relative to the ground; BB drop being relative to the axles). it looks like a drop of 63mm is high enough to work fine for 650B conversion.

I have a couple of 64cm frames that have 650 wheels on them. One also sports fenders and it has good aesthetics, the other no fenders making, to me at least, the wheels look too small.