Condensed answer: SRAM rotors can be used with Shimano disc brakes. The diameter of the rotors should match the system’s settings. The rotors have to be compatible with the wheel’s hub too.
When doing such a conversion, one also has to be cautious of “brake pad overhang”
Requirements for Using SRAM Rotors with Shimano Brakes
1. Proper Diameter
If you want to use SRAM rotors with Shimano brakes, you first have to make sure that the new rotors are compatible with your current set-up.
If the diameter of the SRAM rotors corresponds to that of the existing Shimano ones, you won’t have to change your setup.
However, if you want to upgrade to larger rotors, you will have to install the necessary adapters.
For example, if you’re currently running 160mm Shimano rotors but want to switch to 180mm SRAM rotors, you won’t be able to do so because the rotors won’t fit.
To go from 160mm rotors to 180mm, you will need an adapter which depends on the disc mount that the frame and fork have.
The possibilities are:
International Standard (IS). The brake caliper is attached to the frame and fork via bolts screwing perpendicularly to the mount. This is an older standard, and you will not find it on modern suspension forks.
If you have IS mounts and want to switch from 160mm to 180mm rotors, you will need a +20 IS to Post Mount adapter.
Post Mount (PM). This is the most common disc brake mount. The caliper is mounted via bolts going directly into the mount.
If you have PMs designed to run 160mm rotors by default and want to upgrade to 180mm rotors, you will need a 20mm post mount adapter.
Flat mount (FM). This is a fairly new disc mount common for road bikes. The mounts are very slick and discrete. Flat mounts are limited to 160mm rotors.
2. Hub Compatibility
The rotor that you’re installing must be compatible with the wheel’s hub.
Currently, there are two options:
Bolt-on hubs. In this case, the rotor attaches to the hub via bolts.
Centerlock hubs. Centerlock hubs rely on a Shimano patented technology. The rotor is mounted and secured to the hub via a lock ring similar to that of a cassette.
If you have bolt-on hubs, you will need a bolt-on rotor.
If you have a center lock hub, you have two options:
- Install center lock rotors
- Install bolt-on rotors by using an adaptor
The thickness of the rotors should also be taken into consideration.
SRAM rotors are 1.85mm thick (source) whereas Shimano rotors have a thickness of 1.8mm (source).
Since SRAM rotors are ever so slightly thicker, you will have to reset the caliper’s position to avoid brake pad rubbing.
Brake Pad Overhang
The brake track on a rotor is the area designed to come in contact with the pads. A narrow brake track or a specific disc brake set-up may result in “brake pad overhang“.
Brake pad overhang is a situation when a portion of the pad doesn’t touch the rotor. As a consequence, the “hanging” part of the pad does not experience any wear while the rest of the pad gets slimmer with use.
If the overhang is severe, the two unworn areas of the pads may touch each other and render the brakes useless because the slimmer section of the pads, the one that rubs against the rotor during braking, won’t be able to grab the rotor.
Note: The rotors alone are not the only possible culprit. Sometimes brake overhang is caused by an adapter that’s too large for the current rotors. As a result, the caliper moves too far away from the rotors and leaves the pads “hanging”.
To minimize the chances of experiencing this problem, it’s advisable to measure the current brake track of your rotors and compare it to that of the new set.
Also, the set-up should be inspected after installation. If the pads are too far away, you may be using the wrong adapter and/or shims.
What About Brake Pad Material?
Brake pads are classified into two categories according to the material that they’re made of:
In general, most rotors can operate with both types. One exception would be Shimano’s entry-level rotors which are softer and labeled as “resin only”. Using them with metal pads would result in premature wear.
If you’re going to switch from one type to the other, it’s recommended to softly sand the rotor, thoroughly clean it, and bed the pads.
The Benefits of Using SRAM Rotors With Shimano Brakes
- No need to buy new rotors. If you have new Shimano brakes, and your current SRAM rotors are compatible, you won’t have to spend money on new rotors. The saved cash can be used for new pads, for example.
- Extra choice. If your bike shop is low on Shimano rotors, you can use a SRAM one.
The Downsides of Using SRAM Rotors With Shimano Brakes
- Higher chances of brake-pad overhang (this problem is explained above.)
- Voided warranty (possible but not 100% certain)
The tables below compare the weight of Shimano and SRAM rotors:
|SRAM CenterLine||114g||Shimano SM-RT86||135g|
|Sram Centerline XR Rounded||131g||Shimano RT-MT800||108g|
|SRAM Paceline Rounded||112g||Shimano RT-MT900||108g|
|SRAM Centerline X||101g||Shimano SM-RT70||108g|
|SRAM Centerline Rounded||146g||Shimano SM-RT86||154g|
|SRAM Centerline X Rounded Edges||125g||Shimano RT-MT800||132g|
|SRAM Centerline Rounded||192g||Shimano SM-RT86||187g|
Summary: What You Need To Know
- It’s possible to use SRAM rotors with Shimano brakes. The diameter of the rotors has to match the set-up. If you plan on switching to larger rotors, you will need adapters. The type of adapters depends on the disc mount that the frame and fork have.
- It’s recommended to compare the brake tracks of the old and new rotors and examine how much of the pads contacts the rotors. If there’s too much “brake pad overhang”, the system is considered unsafe. Ideally, the entire surface of the brake pads touches the brake track during deceleration.
- Once the new rotors are installed, you will have to re-adjust the calipers’ position to avoid brake pad rubbing.