27" rims have a bead diameter of 630mm. 650B rims have a bead diametet of 584mm. That's a 23mm difference in radius, and where the brake track is on the rims.
On 26" mtn frames with 24" wheels, which is a similar difference (26mm), canti brakes and V brakes ususually do not have the range of adjustment to accommodate the smaller wheel diameter. Unless you use Paul BMX V brakes which have a longer slot for the brake pad to slide up and down in. But these days, most dudes are using disc brakes when they go from 26" to 24".
I think you should try it anyway- I have a 27" wheeled tandem that is kinda big for me, so I'm interested in what you find.
Tom Martin Oakland CA On topic, then off topic, then on topic again.
-----Original Message----- From: hersefan@comcast.net [mailto:hersefan@comcast.net] Sent: Sunday, June 05, 2005 10:40 PM To: Mark Stonich; classic list Subject: Re: [CR]Changing 27" to 650B
I'm not sure the math is correct - a large 650b tire and a 700c tire have very similar diameter - not as much difference as the post suggests I believe.
Also, be sure you're not going by "modern" conventions regarding standover. In my experience, not nearly as much standover is needed as is often suggested. But if you take my advice and your singing soprano, forget you ever read this post!
Mike Kone in Boulder CO
> At 6/5/2005 10:58 PM -0400, Roy H. Drinkwater wrote:
> >Jerry Moos asked:
> >>Anyone ever installed 650B wheels on a bike designed fot 27"? I'm
> >>looking at a tandem which is very attractive except that the
> >>standover height is 1/2" to 1" too high with 27" wheels. 700C wheels
> >>will only lower it 4mm, so I'm considering 650B. That should lower
> >>it nearly an inch, but will the rims then be too low for the brake
> >>pads? (It has MAFAC cantilevers). Anyone ever done this?
> >
> > Just finished one up tonight, I had a pair of DiaCompe 750's but
> > they were still too short for the rear. I had to make a Sheldon drop
> > bolt, see .
>
> Might work, but the brake arms *may* foul the existing canti pivots.
>
>
> Mark Stonich;
> Minneapolis Minnesota
> http://mnhpva.org
> http://bikesmithdesign.com