Road Bike to Disc Brakes Conversion: Parts Needed and Buying Tips

Points to Consider When Converting a Road Bike to Disc Brakes

The Frame and Fork Standards Are the Most Important

The most crucial factor when converting a rim brake road bike to disc brakes is the “frame and fork.” This is because the disc brake caliper mounts in a different location than the rim brake caliper.

Therefore, the first thing to check is whether the current rim brake road bike has mounting tabs for disc brakes. If there are no mounting tabs, you will need to replace the frame and fork, which means you’ll be reusing the rim brake parts rather than fully converting to disc brakes.

The wheel mounting standards are also important. Disc brake wheels typically use “front: 100mm x 12mm/ rear: 142mm x 12mm through axles.” Since most new wheels are manufactured with this standard, if your frame does not support this, selecting the right wheels will be quite challenging.

Other Parts Besides the Frame and Fork Can Be Managed

If the frame and fork standards are compatible, you can usually manage the rest by simply purchasing the necessary disc brake parts. Some of the current rim brake parts may even be reused.

That said, it can turn out to be more challenging than expected. It’s definitely not a simple upgrade like “let’s just try converting to disc brakes!”

Especially considering that the frame and wheels are some of the most expensive parts on a road bike, replacing them could mean you’re essentially rebuilding the bike from scratch.

It may sometimes be cheaper to purchase a complete disc brake road bike and transplant only the reusable parts from your current bike, so it’s wise to calculate the total cost before diving in.

Parts Needed for Converting to Disc Brakes

Disc Brake Compatible Frame and Fork

This is the most expensive part of the conversion.

To install disc brake calipers, you need specialized mounting tabs, so a frame or fork designed for rim brakes cannot be used as is. You’ll need to get a frame or fork that has disc brake mounting tabs.

Forks aren’t too expensive on their own, and they can be replaced with the right tools. However, for the rear brake, frame replacement is required.

Disc brake adapters for frame dropouts are available, but they are often not very sturdy, so it’s generally necessary to replace the frame with a compatible one.

Given this, it may actually be more cost-effective to buy a budget disc brake road bike from the start.

Disc Brake Specific Wheels

Since disc brakes require the installation of disc rotors, you will need wheels specifically designed for disc brakes.

Most disc brake-specific wheels are marked with “Disc” or “DB (disc brake)” in their product name, so check for these labels when looking for wheels. Also, verify that the wheels match your frame’s dropout width (OLD = Over-Locknut Dimension).

While rim brake wheels commonly use quick release, disc brake wheels now mainly use through axles.

Through axles are different from quick release in that they are threaded on both ends and screw directly into the frame’s dropout. Therefore, your frame must also support through axles to use these wheels.

However, there are adapters available to convert through axles to quick release, so that could be an option.

Disc-Specific Brake Calipers

Since disc brakes work by gripping a disc, they require specialized brake calipers that are completely different from conventional rim brake calipers.

Disc brake calipers are sold by brands like Shimano and Tektro. Price-wise, even the Shimano SORA-grade BR-R317 costs over $30 for just the caliper, making it somewhat more expensive compared to rim brake types.

Additionally, there are two types of brake calipers: “mechanical” ones controlled by a cable and “hydraulic” ones controlled by hydraulic fluid. In Shimano’s lineup, lower-grade models use mechanical calipers, while higher-grade models use hydraulic ones.

Disc Rotors

The disc used in disc brakes is called the disc rotor. Disc rotors are also sold by Shimano and Tektro, with prices ranging from under ¥2,000 for cheaper models to over ¥6,000 for high-end DURA-ACE models. You will need to purchase two rotors, one for the front and one for the rear.

Rotors are available from various manufacturers, and they come in different mounting types: “Center Lock” and “6-bolt” systems. If you’re using a Center Lock rotor, specialized tools may be required, so check the mounting method and necessary tools when purchasing your wheels.

Also, rotors come in different sizes, with each brake system having a recommended size. For example, the BR-R317’s recommended rotor sizes are 160mm or 140mm.

Hydraulic Disc Requires Specialized STI Levers

There are two types of disc brakes: the traditional “mechanical” ones that use cables and the “hydraulic” ones that use oil pressure to apply braking force.

For mechanical disc brakes, since they are still cable-operated, you can use the same STI levers that you had with rim brakes. However, for hydraulic disc brakes, the levers need to incorporate hydraulic mechanisms, meaning you’ll need specialized levers.

For example, Shimano’s GRX group, which is designed for gravel bikes, only offers hydraulic-specific STI levers, making them incompatible with mechanical brakes.

For DURA-ACE, ULTEGRA, and 105, mechanical brakes were previously the standard with hydraulic versions as an option. However, with the release of the new DURA-ACE R9200 series and ULTEGRA R8100 series in 2021, hydraulic disc brakes have become the main option, with mechanical brakes now being optional. As a result, it is likely that higher-end models will primarily use hydraulic brakes in the future.

Additionally, maintenance of hydraulic disc brakes requires more advanced procedures, such as oil adjustments for the levers and centering the calipers, so it’s safer to have a professional shop handle these tasks.