How to find the right disc brake rotor for your bike

When it comes to finding the right disc brake rotor for your bike, the various numbers and measurements can seem confusing, so we’ve made it as simple as possible to help you source the right one for you and your bike.

Disc brake rotors are the metal component that mounts to the hub of a bike wheel and provides the braking surface in a disc brake system. They’re the area that your brake pads grip onto when you want to slow down or come to a stop.

Having a good quality disc brake rotor is essential for braking performance, and they come in various sizes and designs depending on how and where you ride.

Rotor Sizes

Rotors vary in diameter, and bigger generally means stronger braking and better heat dissipation, but also added weight.

Road bikes generally use smaller, lighter rotor, which allow for better weight distribution and better control, especially when performing technical descents. The lack of weight also keeps the road bike light and nimble.

Cross-country and trail or mountain bikes use a slightly heavier and larger rotor, as mountain bike brakes take more of a beating than road bike brakes, and while you’re tackling a steep descent, you’re more likely to need to stop quicker and use your brakes more harshly.

The largest and heaviest disc brakes are typically those of enduro or e-bikes, as the weight of an e-bike is much greater than that of a traditional bike, due to the heavy nature of the frame and battery, so the stopping power needs to be much greater.

Below, we have highlighted the typical rotor sizes for various bike types.

• Road/Gravel/Cyclocross:140–160 mm
• Cross-country/Trail MTB:160–180 mm
• Enduro/Downhill/Heavy E-bikes:180–220+ mm 

Rotor Materials

Most disc rotors are made from stainless steel, because they have to be strong enough to take the impact of quick stopping, and most rotors are made from stainless steel for durability.

Cut-outs and slots in the rotor help shed water and debris while also improving heat dissipation as the rotor warms up from brake pad friction.

Some performance rotors use floating designs (steel braking surface on an alloy carrier) to resist warping and improve heat handling, or sandwich or finned constructions (like Shimano IceTech) to help spread heat away from the braking surface.

Bigger rotors are especially useful if you often ride technical terrain or hit long descents where your brakes get hot.

When it comes to attaching your rotor to your bike, there are two main mounting standards.

The first is the 6-bolt hub, which uses a standard pattern of six small bolts. This is the most common option, as it’s a simple, reliable design and is widely compatible with most bikes and hubs.

The second is Centre Lock, which uses a splined interface secured with a threaded lockring. This system makes rotors quick and easy to swap, but it does require a specific cassette or Centre Lock tool to install and remove the lockring.

Brake pad compatibility

When it comes to finding the correct brake pads for the rotor you’re using, it’s a fairly simple job. Technically, you can run any brake pad, whether it’s organic, sintered, or semi-metallic, with any rotor, as long as you bed the pads in properly after installation.

To bed in your brake pads, make sure your rotors are clean, and your brake pads are brand new. Practice braking on a quiet, flat stretch of road, starting with gentle braking and gradually building up to harder stops. Once you’re confident your bike can perform an emergency stop, you’re ready to roll.

When to replace your rotors

As your rotors wear down naturally over time due to the brake pads squeezing the rotor, you’ll need to replace them once they become thinner than the manufacturer’s recommended minimum thickness. For example, Shimano suggests replacing 1.8 mm rotors when they wear down to less than 1.5 mm thick.

It’s pretty simple, stick to the advice given. However, if your brakes aren’t performing well or they show signs of damage, you really need to get them checked as soon as possible.

At Halfords, we provide a free Bike Health Check, where one of our in-store bike experts will thoroughly check over your bike, including your brake system, to advise whether you’ll need any parts replacing.

How to choose the right rotors

So, how do you know if you’ve found the correct rotors for your bike?

There are a few steps that you can take to make sure you’re investing in the right one. Firstly, you can match your existing rotor, taking the same brand and size compatibility as what is already on your current bike – with this option, you can’t really go too far wrong.

Or, if you’re looking for an upgrade, you can pick the rotor size that suits your riding needs. Think about the amount of power and head management you’ll need from your rotor and then decide what the appropriate thickness is for your bike. Some brake callipers are not designed for thicker rotors, so check the manufacturer’s specification before purchasing.

Some brake callipers aren’t designed for thicker rotors, so check the manufacturers

If you’re going up a rotor size, then don’t forget that you might need to make a few more adjustments using some brake mount adaptors to ensure that the rotor fits perfectly and you aren’t compromising on braking performance.

Now that you know everything there is to know about brake rotors, why not shop our range over at Halfords.com. Here, you’ll find various sizes from a range of trusted cycling brands such as Clarks, SHRAM and Shimano.