26″ inch wheels operate with rims that are 559mm in diameter. 650b wheels are larger and thus require rims that are 584mm in diameter.
As a result, the pads of rim brakes end up lower than the brake track of the rim when converting from 26″ to 27.5″ wheels. (Note: 27.5” wheels and 650b are the same sizes.)
The ideal situation is to have disc brakes as they don’t create this issue. A disc brake consists of a caliper that grabs a rotor mounted directly to the wheel’s hub. The rotor is always in the center of the wheel regardless of the rim size.
When switching from 26” to 650b wheels, disc brakes do not have to be replaced as their work is not affected by the bigger rim.
FAQ: Can I install disc brakes on my bike?
The bike can accept disc brakes only when the fork and the seat stays have mounts for disc brake calipers. It’s easy to know that by examining the fork and the seat stays. There should be two threaded holes near the front and rear axle. The calipers are secured by bolts screwed into those threads.
If you have rim brakes that can’t catch the rim, one of the options is to get a new model with greater reach.
The rim radius of 26″ wheels is 279.5mm. Meanwhile, the rim radius of 27.5″ wheels is 292mm.
The new rim brakes will have to make up for the 12.5 mm difference. (292-279.5=12.5mm)
The key to determining whether a set of rim brakes fits is to look at its dimensions. The dimension property indicates the reach of the brakes.
The ideal candidate would be rim brakes that have dimensions that vary by at least 12.5mm. One example would be Tektro’s R559 long-reach calipers. That model has 55-73mm (18mm difference) dimensions.
Note: It’s also very important to clarify that the position of the brakes matters too. For example, one set of long-reach brakes may be enough to cover the gap but only when the same fork is used. If the conversion requires a new fork too, the new unit may have its break mount(s) higher. As a result, it may be necessary to find brakes with an even longer reach.
To avoid this problem it’s recommended to calculate the maximum reach of the current (non-working brakes) brakes and then add the extra length needed to reach the new rim. The final number is the reach that the new brakes have to offer.
It’s also worth mentioning that the front and the rear of the bike could require brakes with different reach. For example, one model could offer sufficient reach when installed at the back of the bike but fail to reach the rim when placed at the front.
The Greater The Adjustability The Better
Ideally, the brakes will offer a lot of brake shoe adjustability. The longer the amplitude of movement, the higher the chances of success. Some models like the cantilever TRP Revox brakes allow the user to adjust not only the height of the brake shoes but the angle too.
Meanwhile, some entry-level cantilever brakes do not permit the user to move the brake shoes at all.
Below you will find a list of brakes that could work for this conversion. (Ultimate compatibility is not guaranteed as every setup is different).
- Caliper Brakes
|Tektro Tektro R559||53-73 mm|
|Sidepull Synchron||60 – 80mm or 71 – 91mm|
|Shimano 105 BR-R560||57mm|
|VeloOrange Grand Cru||47-57mm|
|Grand Cru Long Reach||47-57mm|
In this case, we’re looking for cantilever brakes allowing the user to move the brake shoes up and down. Unfortunately, most models cannot do that. That said, there are exceptions listed below:
- Shimano Br-cx50
- TRP Revox
- Tektro CR720
- Tektro CR510
- Avid Shorty 6
- Shimano CX70
Note: The vertical adjustment that cantilever brakes offer isn’t as long as that of long-reach caliper brakes.
When looking for a set of V-brakes, the best option are models that allow the user to adjust the brakes shoes vertically. Most basic models do not provide that feature.
One of the cheapest options would be to get BMX V-brakes with a long reach. The list below contains some examples:
- Box One Pro
- Box Two Pro
- Box Three Pro
- Bombshell 686
Another model that isn’t technically a BMX brake but offers the aforementioned functionality would be Paul Component’s Motolite V-brakes.
Note: V-brakes can be installed on the same bosses as cantilever brakes. The advantage of going this route is that there are more models to choose from. Additionally, V-brakes are considered a more advanced technology (read more).
A few products can help with this conversion without getting new brakes.
- V-Brake Boss Elevators
There are adapters that screw onto the original V-brake mounts and elevate the brakes. In most cases, the elevation will be enough for the pads to reach the new rim.
The downside of this approach is that the adapters create another point of possible failure (the extra threads).
On the good side, they’re simple and available at many online stores.
- V-Brake Blocks/Extenders
There are also 700c brake adaptors that keep the brakes on the same mounts but elevate the pads instead. Those models look a lot cleaner than the other options but reduce the original mechanical advantage of the brakes because the pad sits higher on the brake arm.
As a result, the brakes will not perform as expected and may even have insufficient stopping power.
- Clamp-on V-brake Bosses
Another option is to get clamp-on V-brakes bosses that can be installed higher on the bike’s chainstays or the fork’s legs.
The downside of this approach is that clamp-on V-brakes are an exclusive product and thus hard to find.
- Weld/Braze a New Set of V-Brake Bosses
If you know an experienced steel frame builder, you could pay him to cut the old V-brake bosses and weld a set of new ones a bit higher. Make sure that the person in question has the necessary experience to complete the task. Otherwise, your safety will be compromised.