Wednesday, March 27, 2013

650a San Marcos

We've had a few emails asking if it is possible to convert the Soma San Marcos 700c frame to 650b.

(via FreeRange Cycles in Seattle)

Of course the smaller versions of the San Marcos are designed for 650b, however the larger frames have a lower bottom bracket, which can cause issue when moving to a smaller wheel size. There is another option though.

While less talked about these days, 650a also know as 26x1 3/8" can be used to give your 700c SM a little more cush. 650a is nominally halfway between a 700c and a 650b size rims. There are actually quite a few good tires still available in this size from Michelin, Kenda Schwalbe and others, but the absolute best option IMO is the Panaracer Col De La Vie 650a. It's essentially the same as the 650b version, but fits on a 590 ISO rims.

There aren't as many good rims choices, but there are a few. The Sun Cr-18 is the most common, but there's are also the Araya SP-30 and the Velocity Synergy (not currently in production but NOS rims are out there).

This is great news for anybody with a Nottingham Raleigh Three Speed or a classic Japanese Randonneur that's built for 650a rims, but also for anybody looking to retrofit a bike with longer axle to brake bolt measurement such as the San Marcos or bikes made for 27" wheels. Most of the brakes that work for 650b conversions should also work with this trick. My favorite options are the Rivendell Silver dual pivots and the Dia Compe 750 center pull calipers.

(Now available with recessed hardware and upgraded brake pads)

If for some reason that won't work on your frame, there's always the option of Sturmey Archer drum brakes. More info about those can be found here

If your local bike mechanic gives you a weird look when you ask about this stuff, just point them to our distributor in San Francisco and they should be able to help out.

It looks like there's also a Flickr groups dedicated to this tire size now.

Check it out here


Anonymous said...

I prefer the 590 CdlV to the 650B version, it seems to be wider, better made and fits well on the CR 18. Some 650B CdlVs refuse to seat themselves properly on Synerges.

I've upgraded many an old bicycle with the Dia Compe center pulls but I've always had to find a longer bolt for the front brake. Sometimes this involves buying a used shorter reach set just for the bolt. The used center pulls find in parts bins are almost always the short reach model, unfortunately.

The extra long reach tektro is available with nutted bolts but as far as I know the Dia Compe isn't. Some should do something about this. Please.

Evan Baird said...

@Anon Dia Compe also make a nutted caliper brake.

Anonymous said...

If I wanted to use an ugly sidepull on an attracted older bike I could just order the new Tekro brake. What the world needs is a Dia Compe 750 with nutted bolts for older bikes. I guess I should spend some time on McmasterCarr to see if I can find anything that could be made to work.