Most "racing" bikes used these days have 700c wheels. That is a size label not a measurement. The rims are 622mm in diameter. The old classic mountain bike rims referred to as 26" are 559mm in diameter. So why would I care about a size in between?
Jan Heine, in his magazine Bicycle Quarterly, has done a lot of research into cycling in Europe in past decades beginning around the 1930s. He discovered a few interesting things about the equipment they used and what long distances the riders commonly were able to ride in a day: hundreds of miles.
One item of interest was the wide tires Europeans used. Most Americans have been brought up believing that narrow, high-pressure tires are fasssst. But Jan started to question this due to the ride reports from early randonneuring in France. He decided to do some scientific tests and found that wider tires with compliant side-walls were actually faster than the same model of tire in a narrower version. What he decided was that, on real roads, that are rough and not anything like the steel drums used to test tires indoors, high pressure tires bounce off every imperfection in the road. The whole time they are airborne they are not moving the bike forward. He found that wider tires that conform and smoosh around the imperfections stay in contact and keep driving the bike forward. So the wider tires can actually be faster than an identical design in a narrower version.
So back to our story... After coming to this conclusion he found that there really were not available any good quality tires, for typical American road bikes in the 700c size, that were wider. But the old French size of 650B, at a diameter of 584mm, was still in use and wide high quality tires were available. So the 650B size gained a fan club because of the comfortable ride that they afford without a loss of speed or efficiency.
The interesting thing is that older 700c sport touring bikes of the 1970s, that can't use wider tires, are good candidates for a conversion to 650B. Since the 650B wheel is smaller it gives more clearance on the same bike that did not have any clearance using the larger original 700c wheels. So you can give new life and purpose to an old bike doing a 650B conversion.
There is some fine print tho'. First, when you put smaller wheels on the bike the bike gets closer to the ground. If the original design was low to the ground in the first place then lowering it even more can cause your pedals to hit the ground. The other issue is that caliper brakes have to be longer to reach the smaller rims and so you probably will have to get longer brakes or have a frame builder braze on cantilever studs to use "mountain bike" style brakes. There is only so much range of longer brakes available so it just depends on the candidate bike you want to convert. If the original bike used "short reach" brakes then it will be easier to find longer reach brakes for the conversion.
I wanted to do a 650B conversion for my wife to use for gravel road riding and vintage rides. My choice of "donor" was a 1963 Peugeot PA10 (probably). I disassembled the old wheels and bought new 650B rims from Velo-Orange. They make rims that look vintage but are modern construction. I used a french Nervar crackset and bought new Velo-Orange chainrings for a wider range of gearing because the bike came originally with a narrow range of chainrings on a cottered crankset. What this means is that the crank was steel (i.e. heavy) and pinned on the axle with a cotter pin making it difficult to remove and clean. Which is a real pain in my opinion. I wanted a little easier bike to maintain.
Then I found Dia-Compe brakes that were long enough to reach the new position of the rims. Remember that this distance is different for every bike even if they all use 700c wheels originally. It depends on the original clearance for fenders and such.
I tried to keep most everything else original or looking original but I am not slave to tradition. I used a sealed bottom bracket and got rid of the original simpex plastic derailleurs and as mentioned before the steel cottered crank. I used fenders and Panaracer 40mm Col de Vie tires from Velo-Orange.
I just finished the build today and the verdict was that she could easily tell how comfortable the tires were! It was a big hit.
For more information on 650B conversions check-out "650B Conversion Guidlines" on the bikeman site.
|The new owner approves!|