Condensed answer: V-brake levers are compatible with mechanical (cable) MTB disc brakes. However, V-brake levers cannot operate with road disc brakes because road brakes require a different cable pull.
V-brake Levers and Mechanical Disc Brakes
Mechanical disc brakes are cable-operated and therefore need a cable pulling lever.
V-brake levers fit the description but only in the case of mountain bikes.
V-brake levers offer a greater mechanical (leverage) advantage than caliper and cantilever brakes thanks to the longer arms and more advantageous pulling angle.
As a result of the extra leverage, V-brake levers have to pull more cable than the levers designed for road and cantilever brakes.
The term mechanical advantage describes the ratio between the output and input force in a system.
The mechanical advantage of a tool (in this case brakes) is high when the output force is greater than the input force.
When the mechanical advantage is displayed as a form of displacement, however, the formula is reversed.
A high mechanical advantage requires the input displacement to be greater than the output displacement.
In the case of V-brakes, this means that the levers (output units) travel more than than the brake arms (input units).
This may sound a little confusing, but the confusion should disappear upon observing the operation of a lever.
If we use the long arm of a lever to insert force, we enjoy a greater mechanical advantage multiplying our effort.
The long arm (the one with more mechanical advantage), has a longer travel than the shorter one. (image below)
Or in other words, the input is longer than the output.
When the mechanical advantage is low (we use the short arm of the lever), the output displacement is shorter.
This principle translates to the following outcome in the world of bicycle brakes:
Since V-brake levers create a smaller output displacement (movement of the brake arms), they have to pull more cable to compensate.
If this condition isn’t met, the brake lever will bottom out before the brake arms have locked the wheel.
Conversely, caliper and cantilever brake levers cause a greater output displacement (movement of the brake arms).
As a result, they have to pull less cable, or else the brake levers will lock the wheel before the lever has reached its full travel.
This will result in poor braking modulation (control over the braking force).
Differences Between Mechanical MTB and Road Disc Brakes
- Cable pull
Mechanical road disc brakes have to be compatible with cable-operated brake-shifters – the levers/shifters seen on modern road bikes.
Meanwhile, brake-shifters have a “short pull” because they have to be compatible with road-style rim brakes – calipers, most of the time.
Thus, a mechanical road disc brake needs to be adjusted for a short pull lever or else the brake lever will lock the wheel too fast and offer poor braking modulation.
On the other hand, V-brakes are an MTB rim brake. Thus, when disc brakes hit the MTB scene, the mechanical versions were made with V-brake levers (long pull) in mind.
If you combine a road brake lever with an MTB mechanical disc brake, the lever won’t pull enough cable to lock the disc rotor before bottoming out.
The other difference is the mount used for the disc brake – road brakes use flat mounts whereas most MTBs rely on a post mount.
In the case of flat mounts, the caliper attaches to a flat part of the fork or frame. The goal is weight saving and simplicity.
Post mounts, on the other hand, aren’t flat and protrude out of the frame and fork.
The mount itself has no effect on the lever needed for the proper operation of the brake.
Road V-brake Levers
Some companies make V-brake road levers. Those are road bike hood-brakes with a cable pull adjusted for V-brakes or mechanical MTB disc brakes. You can install those levers on a bike with drop bars that uses the aforementioned brake systems.
The downside is that the levers do not have a shifter in them. Thus, you will need a separate shifting system – e.g., downtube shifters, stem shifters, bar-end shifters.
Summary: What You Need To Know
- V-brakes are originally an MTB product. They were engineered as powerful rim brakes meant to replace the previous model (cantilevers). V-brakes were successful at their job.
- V-brake levers offer more leverage (mechanical advantage) than cantilever and caliper brakes thanks to the longer brake arms and the more advantageous pulling angle. As a result, V-brake levers have a greater amplitude of movement.
- To avoid bottoming out of the lever before the wheel is locked, V-brake levers are engineered to pull more cable than cantilever and caliper brakes.
- After the introduction of disc brakes, the mechanical models made for MTBs were engineered to work specifically with V-brakes levers. Thus, V-brakes levers are fully compatible with mechanical MTB disc brakes.
- Road brake-shifters are designed for caliper brakes. Thus, they pull a shorter amount of cable due to the lower mechanical advantage. As a result, the disc brakes engineered specifically for road bikes are not compatible with V-brake levers. They work only with brake-shifters and brake levers designed for cantilevers, caliper, or mini V-brakes.