Published on December 22nd, 2014 | by Brett
Rubber Side Down | Disc Brake Adapters
When you spend most of your time shredding hard, it is important to have safe and reliable brakes that will be there for you when it really matters. Whether you’re building a new bike, replacing worn out parts or upgrading your current setup, it’s hard to know what is compatible in the world of disc brakes. There are so many different frame and caliper mounting standards that it can be dizzying trying to find the right adapter. This guide will help you figure out what you need to match your frame to a desired caliper and rotor combination.
Step 1: What style mounts do my frame and fork have? Different mounting standards front and rear may require caliper adapters.
Post mounts consist of two posts extending from the frame or fork with threaded holes that are perpendicular to the wheel’s axle as seen in Diagram 1. The two holes are spaced 74mm apart center-to-center. There are different post mount lengths depending on the minimum intended rotor size.
International Standard Mounts, designated IS Mounts, are tabs extending from the frame or fork with two threadless holes through them that are parallel to the wheel’s axle as seen in Diagram 2. IS holes are spaced 51mm apart center-to-center and unlike the varying post mount lengths, there are only two IS standards that are each front and rear specific.
Step 2: Select the rotor size and mounting style you need. It is usually smarter to use a larger rotor on the front wheel because most of your weight will be on the front wheel under heavy braking conditions and larger rotors provide more leverage. This is why IS tabs are setup with a 20mm difference in size front to rear. Rotor mounting will either be a standard 6-bolt style or a Shimano Center Lock style. Diagram 3 below shows the difference between 6-bolt and Center Lock standards.
Step 3: Selecting a caliper. Most calipers today from Shimano, SRAM, Magura and others are post mount. This leads to a few different scenarios:
- Post Mount Caliper to Post Mount Fork/Frame: Directly to your frame or fork (Rotor size will be determined by post mount frame standard, i.e. 140 Post, 160 Post, 180 Post, 200 Post or 203 Post)
- Post Mount Caliper to Post Mount Fork/Frame: Bolt to your frame or fork with an adapter (You can choose the adapter that will allow your frame standard to work with the desired rotor size)
- Post Mount Caliper to IS Mount Fork/Frame: Bolt to your frame or fork with an adapter (You can choose the adapter that will allow your frame standard to work with the desired rotor size)
The compatibility chart below will help you to select the proper calipers, adapters and rotors based on your desired setup. Feel free to browse our complete Mountain Brake Adapter category as well. If you are still having issues, feel free to give Art’s Cyclery a call at 1.800.626.3440 and we will help you through the process.
Rubber Side Down is a weekly column dedicated to the fledgling cyclist in all of us. Art’s Cyclery Web Content Editor, Brett Murphy is not a professional cyclist, and doesn’t try to masquerade as one either, but he does love to ride bikes. Whether you are clipping in for the first time or counting down the days until your first race, read on, learn from his mistakes, and keep the rubber side down.
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