I found this web page on Tektro's website very helpful. It lists all the tektro's
non-disc brakes. when you click into each brake product, the page lists the "dimension", which I think is the "brake reach". For example, the
CR720 has a brake reach of 21-35mm. When you convert from 26" to 650b, the change in the radius of the rim is (584mm-559mm)/2 = 12.5mm. It means that the brakes need to be able to reach 12.5mm higher on 650b rims than on 26" rims.
The 14mm (35mm-21mm) range that the CR720 has seems to be OK to cover the 12.5mm raise. However, depending on the placement of the cantilever brake posts, if the "brake reach" of a fork is higher than 22.5mm when using 26" wheels, then CR720 won't work with 650b wheels. Often, the "brake reach" of the front and rear are also different. For example, I converted a
Specialized Rock Combo from 26" to 650b. The rear brake posts allow me to use CR-720, but the front brake posts were placed too high for the CR-720 to work. I ended up switching to V-brakes. Many V-brakes designed for BMX bikes have a very wide range of adjustability. For example, this
Promax brake has 35mm of adjustability in terms of reach (2.5 times that of the CR720)! If you want to keep your short-pull brake levers, you can use the
mini-V version of the Promax brakes. But there are several BMX V- and mini V-brakes that have this feature, which is convenient for wheel conversions.
The beautiful way is to use
Paul Monolite, but as you can see from the price, it's 5 times more expensive than the Promax. One of the pictures in my Rock Combo album has a close-up of the Promax, and it has really decent finish and it works very well--easy to install and adjust, no squeaking noise right off the bat, and has great stopping power.
So way to know for sure is to buy the brakes you want and try it on for size. short of that, you can put a 650b wheel in the drop-out and measure the distance between the middle of the ring to the middle of the brake-post, then consult the Tektro page to see which brakes has the reach range to work.
hope this is helpful,
Franklyn