IS Mount Disc Brakes: Everything You Need To Know

The IS disc brake mount, short for International Standard disc brake mount, is a widely used standard for attaching disc brakes to bicycles. This mounting system is designed to provide a secure and reliable connection between the brake caliper and the bicycle frame or fork.

When it comes to the disc brake mounts on a bike, there are two more types of disc brake mounts other than IS disc brake mount, which are: Flat mount and Post Mount. This article will focus on IS mount brakes while briefly explaining the other two types as well, so keep reading to know everything related to IS disc brake mount.

IS Mount Disc Brakes – Detailed Guide

IS Mount Disc Brake
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The IS disc brake mount has become a popular choice among cyclists due to its compatibility with various types of disc brakes and its ability to accommodate different rotor sizes. With its standardized design, the IS disc brake mount offers versatility, ease of installation, and consistent performance, making it a preferred option for riders seeking efficient braking power on their bikes.

IS Disc Brake Mount
IS Disc Brake Mount

The International Standard or IS mount brakes have unthreaded eyelets that are 51mm apart. The two threadless holes run parallel to the hub axle and are used to mount either an IS caliper or an adapter for a post-mount caliper.

The absence of threads prevents the riders from damaging their bike frames during installation or maintenance. They are also known as IS tabs or disc tabs. In IS mount disc brakes, the brake caliper is further attached to an adapter that has two sets of threads, one for the IS mounts and another 74mm apart for the caliper. 

Flat Mount Disc Brakes

Shimano was the first to introduce flat-mount disc brakes in 2015. The caliper of a flat mount sits directly on the bike chainstay, resulting in more space. Most road bikes, trail and XC bikes use them due to their lighter weight. However, flat-mount brakes are comparatively expensive. 

Post Mount Disc Brakes

The bolts in post-mount disc brakes are 74mm apart and they run parallel to the frame. These brakes are simple and affordable. Since post mount brakes add weight to bikes, they are common for mountain bikes and the first gravel bikes also had post mount brakes. As these disc brakes are easy to install and adjust, many modern frames and forks also utilize them.

Watch a Video Guide about IS Disc Brake Mount

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You can also read a detailed comparison of hope e4 vs v4 brakes

Benefits and Drawbacks of IS Disc Brake Mount

The major advantage of an IS disc brake mount is the threads that are in a relatively cheap and easily replaceable adapter.

The drawbacks of IS disc brake mounts are that they are expensive due to the involvement of an adapter and also they are mechanically complex.

Furthermore, the adapter size for the front and rear is different with IS mount brakes. The smallest size you can use for the front is 160mm. While for the rear, they can even take a 140mm adapter. 

Mountain Bike Disc Brake Adapters

To mount a disc brake caliper on a bike’s frame, some mountain bikes need disc brake adaptors that depend on the size of the rotor you are using. Bikes these days use post-to-post mount frames because they mount directly to a disc brake caliper.

On the other hand, older bikes use an IS-to-post-mount adapter because you need it if you want to use any caliper on your bike. Post-to-post mount is more widely used because sometimes there is no need for an adapter if you have the minimum size rotor.

However, you will be needing a disc brake adapter if you want to ride a larger rotor. Keep in mind using the same brand for both disc brakes and disc brake adapters is better.

What Disc Brake Adapter Do I Need?

Disc brake adapter in simple terms means a piece of metal and two bolts on which you can mount different sized disc rotors to your bike frame. So, it is a spacer.

Also, know that every disc brake does not need an adapter. For example, if the design of a bike frame is for 160mm rotors and post mount brakes, then there is no need for an adapter if you want to use the same size rotor.

Moving on, post-mount adapters are for carbon mountain bikes while flat-mount adapters are common for gravel and road bikes. Adapters allow you to customize brake rotor size. The front and rear rotors of gravel and road bikes are 160mm and 140mm respectively. While for the mountain bikes, the front is 180mm and the rear is 160mm.

You should avoid adapters if there is no need because they add extra weight, a place for bolts to loosen, and extra places for failure. If you have a bike frame designed for 160mm rotors and you wish to have bigger rotors while checking if your bike can support bigger rotors, you can get a 20mm post-mount adapter.

But, if you have a bike frame designed for 180mm rotors, you are only required to directly mount the brake without involving an adapter. Also, if you want to change this 180mm rotor to 200mm, you can get the same 20mm post-mount adapter to do it.

Still, got questions? Move down to read some more answers regarding the IS disc brake. You may also want to know how often to bleed hydraulic bicycle brakes

FAQs about IS Mount

IS vs post mount brakes?

If we look at IS vs post mount, the two bolts In IS mounts are 51mm apart and their placement is perpendicular to the wheel. The two bolts in post mounts are 74mm apart and parallel to the wheel. A post-mount brake does not need an adapter as it screws directly into a bike’s frame. Post-mount brakes are heavier yet affordable whereas IS-mount brakes are complex and expensive.  

What are IS post mount disc brakes?

Post-mount brakes are the standard for mountain bikes in which the bolts are parallel to the wheel and 74mm apart. Since a post-mount brake screws directly into the bike’s frame, there is no need for an adapter. Post-mount disc brakes add extra weight to a bike.

What are direct mount disc brakes?

A direct-mount disc brake mount to the bike’s frame or fork between two mounting points instead of one. This makes them stiff and better than standard single-bolt brakes. The two mounting points make them less prone to flex. 

What are flat mount brakes?

Flat-mount brakes are compact and lighter in weight. Besides, the caliper in a flat-mount brake sits directly on the chainstay. This results in more space which does not happen in the case of a post-mount caliper. In addition, flat-mount brakes are road-specific and some XC bikes use them due to their lightweight.

Final Thoughts on IS Mount Brakes

To sum up, IS-mount brakes were popular in the early 2000s. However, ever since post mounts replaced IS mounts, fork manufacturers stopped producing IS mount brakes. But, IS mounts are still seen on the rear of some frames. Moreover, IS mounts are expensive and have complex structures.

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