Bicycle Disc Brake Mounts: Recognition and Adapter Selection

Types and Features of Bicycle Disc Brake Mounts

There are three main standards for mounting bicycle disc brakes.

1. flat mount
2. post mount
3. international mount

The current mainstream is flat mount and post mount, and most of the sports bicycles released by major bicycle manufacturers in the past few years have these two mounting standards.

As for Shimano’s current disc brake bodies, flat mounts are mainly used for road bikes and post mounts for MTBs, with some flat mounts.

The use of international mounts is also becoming rare nowadays.

International (Internal Standard) Mount: IS

In the early days of disc brakes on bicycles, only the IS standard (Internal Standard) was available.

Unlike post mounts and flat mounts, international mounts are mounted parallel to the frame.

Today, some manufacturers produce IS standard frames, but this standard is rarely seen in new products anymore, including the brake caliper itself.

Post Mount: PM

Following the international mount, the post mount standard was introduced. The caliper is mounted vertically to the frame from directly above. The caliper structure is large vertically, and the frame side must have a large clearance for the caliper, so a frame that can accommodate the caliper must be selected.

Because the caliper can be structurally taller, it can be compatible with larger rotors, and is the standard for MTBs that require greater braking force with 200mm rotors, etc. On the other hand, the caliper can be structurally smaller, and can be installed on lower frames.

On the other hand, it has the disadvantage of being structurally difficult to make smaller and lower in height, so it is no longer used for road bikes.

Flat Mount: FM

Flat mounting on the frame or fork allows the caliper body to be downsized and space-saving. The caliper is mounted from the back with bolts parallel to the mounting surface.

Because of its smaller size, it is mainly used in hydraulic brakes for road bikes.

On the other hand, since it is structurally difficult to add height to a flat mount, it is not possible to install larger rotors, such as 200 mm rotors, and basically only 140 mm and 160 mm rotors can be used.

For road bikes, it is said that 140mm rotors are sufficient if not used at high speeds, and 160mm rotors are sufficient even for professionals. For road bikes, where weight reduction is important, the trend is toward smaller and space-saving calipers with improved braking performance, rather than increasing weight by increasing rotor size.

How to tell the mounting system apart by appearance

Let’s review how to tell the difference between the frame and the brake body by appearance.

How to tell the difference between frame and fork mount standards

It is unlikely that you will make a mistake if you know the difference between which type of disc brake mount your frame/fork has, since they are basically very different in shape.

First, check the mounting orientation. You can tell the difference by the direction in which the bolts are mounted when the brake body is installed. Horizontal = international, vertical = post mount or flat mount.

For the same vertical mounting, the post mount has a U-shaped base and the flat mount has a slight protrusion or no protrusion at all.

How to identify the mounting standard of the brake body

To determine which type of brake body is used, first check the direction in which the bolts are attached to the frame/fork.

As with the frame and fork, horizontal = international and vertical = post mount or flat mount.

The key to determining whether a brake is post-mounted or flat-mounted can generally be determined by looking closely at the shape of the brake body.

At a quick glance, flat-mount and post-mount brakes look similar, but if the brake has a part protruding below the horizontal mounting line (which would interfere with a flat-mount brake), it is a post-mount brake.

You can use mounting adapters for combinations of different standards!

Bicycle disc brakes have a small part called a mounting adapter. By using an adapter, it is possible to change the rotor size and mount different standards.

Resize the rotor with an adapter

The primary use of disc brake mounts is to accommodate different rotor sizes.

Different rotor sizes change the distance from the caliper to the rotor (lower if smaller, higher if larger), so the location of the caliper itself will need to be adjusted. In this case, a mounting adapter is used.

If the rotor size changes, use a mounting adapter with “same mounting standard to same mounting standard”.

Also, basically, it is mainly used when the rotor size becomes larger, and when it becomes smaller, it is either unnecessary or not possible to make it smaller due to the standard.

Installing a brake of a different standard with an adapter

Disc rake mounting adapters can also be used to install different mounting types and different standard brakes.

For example, the photo above shows a case where a post-mounted brake is installed on an international pedestal.

In this way, the mount makes it possible to install a brake even if the standard is different.

How to Read Shimano Disc Brake Mounter Types and Model Numbers

Shimano offers a wide variety of mounting adapters for different applications.

Disc brake mount adapter | Shimano

There are different types of Shimano disc brake mounts for each mount type, and there are rules for the model number. The model number is in the form of “SM-MA-(F/R)(rotor size)(caliper standard)(pedestal standard)”.

For example, SM-MA-F160P/S can be broken down as follows.

• F: Front
• 160: for 160mm rotor
• First P: Post-mounted brake caliper
• S after the slash: Fork on international pedestal

In other words, it is “an adapter to install 160mm rotors and post-mounted brake calipers on post-mounted front forks.

The model numbers corresponding to the mounting standards are as follows

• P: Post mount
• S: International Mount
• D: Flat Mount

Mounting adapter for post-mounted frames and forks

Post-mount brake on a post-mount pedestal.

This type acts as an extension adapter since they are post-mount to post-mount.

The size of the post-mount adapter is determined by which rotor size the frame/fork side pedestal will fit without the adapter.

If the standard rotor size is 140mm, you will need to extend one up to 160mm, 160mm to 180mm and 203mm, and 180mm to 203mm, and choose an adapter for that size. adapters for 160mm and 180mm rotors are dual-use.

The lineup is only available for the front, but depending on the frame shape, it may also be used in the rear.

※The number “000” in the model number indicates the corresponding rotor size

International mount brake on a post mount pedestal

An adapter for using international mount brakes, which I feel are not used very often, on post mounts.

※The number “000” in the model number indicates the corresponding rotor size

Mounting adapter for flat-mount frames and forks

Post-mount brakes on flat-mount pedestals

This is a conversion adapter for installing post-mounted brakes, which are common on MTB disc brakes, on flat-mounted frames and forks, which are the main type of brakes on the current road.

※The number “000” in the model number indicates the corresponding rotor size

Flat mount brake on a flat mount pedestal

This adapter is used for changing the rotor size on flat mounts; only one item in the lineup, the SM-MA-R160D/D, can be used for both front and rear by turning it upside down.

For flat mount, an adapter is required for front brakes, and the SM-MA-R160D/D will accommodate 140mm and 160mm rotors. For the rear, the flat mount is only used for 160mm rotors, as the 140mm mounts directly.

Mounting adapter for frames and forks with international mounts

International Mount Brake on International Pedestal

An adapter to extend the International, which is rarely used these days, allowing the 160mm pedestal to be extended to 180mm or 203mm.

※The number “000” in the model number indicates the corresponding rotor size

Post Mount Brakes on International Pedestals

This adapter is designed to install post-mounted disc brakes on International bicycles, which are the old standard. It is used for upgrading older bikes.

※The number “000” in the model number indicates the corresponding rotor size

The above Shimano disc brake mount adapters can be summarized as follows.

Frequently Asked Questions About Types of Bicycle Disc Brake Mounts

Items mentioned in this article