Conversion candidate frames

[Jason Mansey]

I've been considering a Lightning Bolt for some time but being in Canada it's pretty expensive to import. 

Noticed they sell a stand alone Randonneur fork and it has me thinking I should just do a conversion.

https://crustbikes.com/collections/forks/products/crust-650b-canti-rando-fork

Thinking I could have canti bosses brazed on.

Is this a good candidate frame, believe it's Tange 1? Would a 27" wheel frame play nice with this fork?

[Ian A]

It could be good, but with buying the fork, having cantis brazed on the frame (although you could probably have good results with long reach sidepulls) you might be spending more than anticipated. Plus it would be an experiment which might not be as good as you hope.

What about combing Pinkbike? This could be an option https://www.pinkbike.com/buysell/4091279/

IanA Kitimat BC

[Brad]

Dia Compe 750 or Mafac Raid brakes, 650B wheels (might require getting frame spread or wheels built on 120 spaced rear hub) and your done.   Braze ons are a convenience not a necessity.  Tange tubing is first rate.  The fork appears to have enough rake to now be classified as low trail.  

[Michael Goetinck]

I found this helpful when I started doing conversions.

https://www.bikeman.com/blog/guidelines-for-650b-conversions.html?srsltid=AfmBOoqSEJKOKmRGRpjTlnGmYdNfoMm2pD_khw0iciJ9MOui0eoJwCDF

 

I’ve also found some forks on eBay that had a wide enough crown to accept the bigger tires I wanted to run.

 

Have fun,

Michael H. Goetinck

Snowdog Construction

(802) 649-3605

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[andrewd...@gmail.com]

If you're using a 27" frame with a 650B fork, it'll tilt forward a bit.  For each cm shorter it is from axle to crown, the angle of the headstem will increase by roughly a degree.  And thereby your trail will increase.  There are calculators online for those who want low trail.

[satanas]

The calculators will also help you avoid low trail, or just to figure out what it wil be:

http://yojimg.net/bike/web_tools/trailcalc_dual.php

Later,

Stephen

[Cameron White]

Before digging any new pits to burn monies, first confirm that:

1. Bike handles well to your desired needs.  Up/down hills, carving, flats, carrying a load.

2. It fits you.

3. Does not have any significant frame build quality issues as is so common with old frames.  70s japanese bikes...in my opinion their QA/QC is lacking compared to 80s.  Guessing mid '70s on this Nishiki.  Maybe later, like '77?

4. Has clearance at the chainstays and fork for tire + fender width.

5. You are aware that a bike may/will handle differently once converted to 650b, and you might not like it.

Agreed with the others that the original fork should have enough rake to be considered low trail.  Nishiki made a lot of low trail bikes in the 70s, into the 80s a bit as well.

You're on the money you'd probably need to braze canti bosses on there.  27" >> 650b usually is too far of a brake reach change for long reach calipers.  

[fordb...@gmail.com]

It looks like it might have room for 700 x 38s if it won't work for 650b. 

Ford

Ghent, NY

[Mark in Beacon]

One other parameter to check is your bottom bracket height. A 27" bike will drop further than a 700C, bb drop being equal. 27" x 1 1/4" or 3/8" are also bigger that a 25-30mm tire.

[Jason Mansey]

This is something I've wondered about. 

Your saying bottom bracket height is better maintained when using a 700C frame? 

Are there any favorite frames for conversions?

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[Mark in Beacon]

Bottom bracket drop is a frame attribute that is set, no matter the wheel and tire size. I'm saying if the drop was designed with 27" wheels with x 1 1/4" wide tires to be, say, 10 3/4" height, and another frame was designed with  
700 x 25mm to be 10 3/4" height, when you put 650b wheels on both, the bb height of the 27" frame will be lower than the 700 frame. Hope that makes sense.

[Mark in Beacon]

There is a ton of good information on 650b conversions here on the internets, along with potentially good frames to try.

[Stephen Poole]

BB drop (and thus BB height) is very much a personal preference thing, and will depend on crank length, Q factor, pedal size, one's tendency to pedal around corners (or avoid doing so), etc.

I like low BBs (~260-265mm for road use), but plenty don't; YMMV, depending on the factors above.

Later,

Stephen

[Brad]

Actually, the ERTRO for a 27 x 1/1/4 tire is ....32 x 630.   Bottom bracket height change is another place where research and math can help.  The circumference or the radius for a given wheel can be helpful in a comparison.

622 (the bead seat diamter) for a 700 c wheel yields a radius of 311.

Typically race bikes are designed for a 700 x 23 tire.

So we add 23 to 311 to get the tire shod diameter of 334.

Now subtracting from 334 will get us the comparison.

584 is the bead seat diameter for a 650B tire.

Half of 584 yields 292 as the radius to the tire bead.

 We can add tire sizes to 292 to get comparison numbers on drop.

For a 38 tire we get 330.  

A 14 gauge spoke is 2mm.

330 will be a bottom bracket drop of two spoke widths or 4mm.

For a 42 x 584 tire magically we have the same radius as 700c wheel with a 23 mm tire.

Space between fork blades is now the controlling factor.  A cheap pair of calipers like the ones from Harbor Freight will come in handy here if you don't have a tire shod wheel to shove in there.

[Bernard Duhon]

 

Has anyone tried these v-brake extensions to convert a 700 v-brake bike to 650b  

700c touring bikes always have more tire clearance than the 70-80’s road bikes your posts discuss.  I am thinking instead of squeezing the 38mm 650b you could get ample clearance for 42mm 650b.

 

Box Two V-Brake Post Extender (Black) - Dan's Comp

 

 

 

Yours sincerely,

 

Bernard F. Duhon

Bernard F. Duhon, Ltd.
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From: 65...@googlegroups.com <65...@googlegroups.com> On Behalf Of Brad

Sent: Saturday, April 4, 2026 8:32 AM
To: 650b <65...@googlegroups.com>

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[Brad]

My mistake.  I did the math for a 700c wheel, not a 27" wheel.

700c is 622 in diameter and 311 in radius.

27 inch rims have a 630 bead seat diameter and a 315mm radius.

In ancient times the switch to 700c wheels from 27 inch wheels required a brake with four or more mm of room to adjust the pads down.

[Jason Mansey]

90% sure I'll be picking up a Raleigh International next week. 

I read that the tire clearance over the years hasn't been super consistent. Not sure if the fork can accommodate 42c with fenders.

For my riding 38c is enough. My concern is really related to pedal strike.

Pretty excited about this find!

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[Stephen Poole]

According to Grand Bois' website, their 650b tyres have the following ODs - others (like RH, etc) are likely to be similar:

1. Cypres (32mm nominal width), 652mm OD, so 326mm radius

2. Hetre (older, nominal 42mm width), 669mm OD, 334.5mm radius

3. Hetre Forestiere (current), 672mm OD, 336mm radius

(4. And, FWIW, WTB's Horizon (47mm nominal) was said to have a radius of 342.5mm)

Nominal widths (and radii calculated from them) are likely to be out by a few mm, so will not be reliable - one must measure things on the intended rim; actual tyre width will vary by ~0.4mm for every mm in internal rim width, so WAM (Width As Measured) is only helpful if the rim's IW is specified too.

In practice, 700x23 tyres are likely to have a radius of 336-338mm, provided they're actually close to being true to size, not labelled 23mm but actually  smaller - not uncommon, especially in the 80s.

The radius of the tyre will affect the BBH, but is rarely the limiting factor in whether a wider 650b tyre will fit. That's usually the (nominal) width, which can be a problem at the  seatstays (less likely), fork blades (somewhat more likely, especially if >38mm), and the chainstays (very likely if >32mm). YMMV depending on what frame and fork you have - one must *always* measure, never assume or guesstimate!

Later,

Stephen

On Sun, 5 Apr 2026, 00:58 Bernard Duhon, <ber...@bernardduhon.com> wrote:

 

Has anyone tried these v-brake extensions to convert a 700 v-brake bike to 650b  

700c touring bikes always have more tire clearance than the 70-80’s road bikes your posts discuss.  I am thinking instead of squeezing the 38mm 650b you could get ample clearance for 42mm 650b.

 

Box Two V-Brake Post Extender (Black) - Dan's.

[daxo potato]

these extenders only work on (removable?) canti posts that thread into the frame. I've never seen such posts, I'm told it's a bmx thing. 

if you don't believe me, i have a set I'd sell cheaply 😜 

Dave in NY 

On Sun, 5 Apr 2026, 00:58 Bernard Duhon, <ber...@bernardduhon.com> wrote:

 

Has anyone tried these v-brake extensions to convert a 700 v-brake bike to 650b  

700c touring bikes always have more tire clearance than the 70-80’s road bikes your posts discuss.  I am thinking instead of squeezing the 38mm 650b you could get ample clearance for 42mm 650b.

 

Box Two V-Brake Post Extender (Black) - Dan's.

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