What parts are needed to convert a road bike to disc brakes and what to look out for when buying them.

Posted at: Aug. 27, 2021

Disc brake-equipped road bikes have been on the rise in the past few years. "For those who want to try out disc brakes but don't want to buy a new bike, we've put together a list of the parts you'll need to buy disc brakes and the points to keep in mind when buying.

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Parts required to convert a road bike to disc brakes

Disc brake compatible frame and fork

This is the most costly part.

Disc brake calipers require a special pedestal to be installed, so a rim brake road bike frame or fork cannot be installed as is. You will need to get one that has a base for disc brakes.

Disc brakes need to be mounted on a special pedestal.

Forks are not that expensive and can be replaced if you have the special tools. However, for the rear brake, the frame must be replaced.

There are disc adapters available that attach to the end of the frame, but they seem to have strength problems, so in principle, you need to replace the frame with a compatible one.

If you think about it, it may be more cost-effective to buy a cheaper complete disc brake road bike from the beginning.

Disc brake-specific wheels

Disc brakes require a disc called a disc rotor to be mounted on the wheel, so the wheel needs to be specially designed for disc brakes.

Disc brake-specific wheels are usually labeled “Disc” or “DB (Disc Brake)” in the product name, so when looking for a wheel, check there and also check if it fits your frame’s end width (OLD = Over-Locknut Dimension).

Disc brake-specific wheels have rotor mounting hardware.

Also, while quick release is the mainstream for rim brake wheels, through-axle is now the mainstream for disc brake wheels.

Thru-axles have a male threaded shaft that screws into a female threaded shaft on the end side of the frame, so the frame side must also be compatible with thru-axles.

Thru-axle is structurally completely different from quick release.

However, there are also adapters to convert through-axles to quick-release, so you can use those as well.

Special Brake Caliper for Disc Brakes

Disc brakes require a special brake caliper, which is completely different from a standard rim brake, because the brake is applied by sandwiching the disc.

Brake calipers for disc brakes are available from Shimano and Tektro. In terms of price, even the SORA-grade BR-R317 costs more than $40 on its own, which is slightly higher than the rim brake type.

Disk Rotor

The disc of the disc brake itself is called the disc rotor. Disc rotors are also available from Shimano and Tektro, with the cheapest ones costing less than $20 each and the most expensive DURA-ACE grade costing over $50 each. Since they are used front and rear, you need to have both front and rear.

Rotors are available from various companies, and depending on the wheel, there are “center lock” and “6-hole type” rotor locking systems. In the case of the center-lock type, special tools may be required, so be sure to check the installation method and required tools when purchasing the wheel.

Also, rotors come in different sizes, and the acceptable rotor size is determined by the brake. For example, for the BR-R317 mentioned above, the recommended rotor size is 160mm or 140mm.

Road Bike Disc Conversion and Summary of Checkpoints

Finally, let’s take a look at the parts required to convert a road bike to discs and a summary of checkpoints to choose from.

Parts Checkpoint
Does the frame have a disc brake pedestal?
Does the OLD fit the wheel?
Fork
Is there a disc brake pedestal on the fork?
Does the OLD fit the wheel?
wheel
Wheels Can the disc rotor be mounted?
Is it fixed with quick release or through axle?
Does it require special tools for installation?
Does the OLD fit the frame and wheel?
Brake caliper Select disc specific brake?
Brake caliper Select a brake caliper that matches the allowable brake rotor size
Select a brake caliper that matches the wheel rotor mounting standard

It turns out to be a bigger hurdle than I thought. At the very least, it’s not as easy as “Let’s try a disk upgrade! This is certainly not a casual upgrade.

In particular, the frame and wheels are the most expensive parts of a road bike, so replacing these parts is almost like taking the bike apart. As I mentioned at the beginning of this article.

As I mentioned at the beginning, it may be cheaper to buy a complete disc road bike and transplant parts from your current bike rather than forcibly converting your existing bike to a disc bike, so make sure to calculate the total cost before you start.

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