650B Conversion Project

I finished (finally) the conversion of the SOMA into a 650B machine. For those of you not in the know, 650B is an obscure tire size once most popular among French touring bikes. Lately it's been seeing a resurgence in popularity in large part thanks to Rivendell Bicycle Works and Kogswell Cycles who both produce affordable frames made for 650B wheels. The wheels themselves are slightly larger than the 26" MTB standard and slightly smaller than the 700C standard. Those who have been around for a while might wonder if this doesn't sound a lot like GT's failed 700D experiment from the 90's. It is except that 650B was once popular among numerous builders. Even Raleigh USA made a 650B bike back in the 80's. The size has also maintained life in Japan and France unlike GT's effort which was largely proprietary.

The supposed advantages are a fatter tire running at lower air pressures. This results in a smoother ride and better handling. To listen to some people you'd think 650B will turn a Huffy into a magic carpet. You can put fatter 700C tires on a bike but few frames outside of touring and 'cross can handle much more than 28mm. 26" is often seen as too small a wheel size. 650B is according to the faithful a perfect mid point.

650B is also a nice way to take an old road frame and make it into a more versatile machine sporting fenders and cushy tires. This is the appeal for me and I decided to see if the hype was for real by converting my 700Cx28 SOMA Smoothie ES into a 650Bx38 SOMA Smoothie ESS (Extra Super Smooth!) Beyond the new wheels and tires I also needed new brakes. I've always been a fan of how centerpulls look and a fan of Paul Components so picking up a pair of their Racer brakes was a no brainer (other than the cost!) Everything went together pretty easily. The Pauls just barely had the reach for my new wheels and the existing Berthoud fenders just barely contain the 38mm tires.

My first ride on the new machine was a leisurely 1 hour shakedown ride. At first I really didn't notice much difference except on a short patch of dirt trail. The first real test would come with the 100k Populaire put on by the Seattle International Randonneurs. This ride featured a couple of climbs and some generally craptacular weather (light rain, temp in the 40's, snow slush on the roads). Starting out on the ride it was hard to discern much difference between the new wheels and the old ones. The ride was a bit smoother but that was about it. When we hit the first climb - a short but steep 1/2 miler - I rose up out of the saddle and could definitely feel the difference between the 650B and 700C wheels. The new wheels were noticeably slower to respond. My normal 700C wheels are Mavic Cosmos shod with 700x28 Conti GP folding bead tires. The Cosmos is Mavic's day-in, day-out workhorse riding wheel. By today's standards it hardly qualifies as lightweight though technophobic luddites would call it scary light since it was less than 36 spokes. By comparison, the 650B wheels are 32 spoke affairs laced to rims that are the same as MTB rims and shod with wire bead tires. Bottom line is they weigh quite a bit more and it was pretty noticeable on the ascent particularly when you try to change tempo. To be fair, the biggest shortcoming on that climb was still the rider.

On the downhill the extra traction provided by the 38mm tires was much appreciated, especially on the slick, wet roads. The Col de Vie tires cornered very nicely without any noticeable edge or squirming. The tires did make noticeably more noise than my usually slicks. Not the annoying chased-by-a-swarm-of-hornets noise one gets when riding a MTB on pavement but more of a soft whizzing sound. It didn't annoy me but it could drive other riders crazy.

In terms of handling the bike did feel a little more stable. While it's not as good as a bike with dedicated low trail geometry I did find it easier to stay in a straight line while fishing through my front bag. Low speed stability also seemed better.

So far I'm not convinced that 650B is the wave of the future. It seems to be better in certain niche applications (loaded touring, for example) but for normal day to day riding over average roads I don't see it offering any huge advantages over 700C. As for conversion projects, 650B is a great way to make an old road frame more versatile.