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If you want optimal stopping power from your brakes, make sure you have the disc brake rotors for mountain biking you can afford.
Along with the lever and caliper, the rotor is an essential and, some would argue, the most important component of a brake system. It’s the part the pads clamp onto, it dissipates heat and also creates the leverage and power required to slow you down. So it’s important that you find the best disc rotor for your mountain bike that you can.
SRAM HS2 brake rotor
Great performance for long descents
Size: 160, 180, 200, 220mm | Bolt pattern: Six-bolt or Centrelock | Score: 9/10
SRAM’s latest mountain bike brake rotor is this all-new HS2. At 2mm wide, it’s thicker than the 1.85mm CentreLine discs it replaces, with a weight increase of around 35g for the 180mm size I tested. The braking surface features slanted slots that leave more metal for pads to grab, and the pattern incidentally looks a bit like a flipped version of the old Avid G2 cleansweep rotors that were popular with sponsored SRAM downhill racers.
Brake discs aren’t very glamorous, and Magura and Hayes have been making thicker rotors for years, but this is a killer upgrade for SRAM purists that noticeably improves stopping power with any drawbacks aside from a few extra grams.
Read the full review of the SRAM HS2 brake rotor
Aztec Alloy Steel Floating Rotor
Affordable and compatible with most disc brakes on the market
Material: Alloy steel | Size: 160 and 180mm | Bolt pattern: 6 bolt
Due to the modular construction of a floating rotor they’re generally more expensive but Aztec bucks this trend with its affordable Alloy Steel Floating rotor. It’s nearly 40% cheaper than the Swiss Stop Catalyst Pro, although it does come in limited sizes – Aztec is only offering this one in 160mm and 180mm.
It has stainless-steel braking surface and a machined alloy carrier in a six-bolt pattern. Like most floating rotors the braking surface expands slightly as it heats up, which helps dissipate heat to prevent warping and brake fade. The Aztec disc is drilled for 6-bolt and is compatible with most disc brakes on the market.
SwissStop Catalyst Pro Disc Rotor
Pricy, but unbelivably precise
Material: Stainless steel and aluminium | Size: 140, 160, 180, 203 and 220mm | Bolt pattern: 6 bolt or Center Lock
Swiss Stop makes some of the very best third-party rotors on the market. The Catalyst Pro is a two-piece design a high quality SUS410 stainless steel brake track and riveted to a lightweight 7075-T6 series aluminium carrier. It comes in 6-bolt or Center Lock fitment and comes in 140, 160, 180, 203 and 220mm, although the price shown here is for the smaller two sizes, the 220mm diner plate is a whopping £79.99.
However, you are getting an unbelievably precise rotor with excellent wear characteristic and heat dissipation. Add a set of SwissStop pads and this is the ultimate brake have upgrade.
Clarks Lightweight Stainless Steel Floating Rotor
Great budget brake rotor
Material: Stainless steel | Size: 160, 180 and 203mm | Bolt pattern: 6 bolt
If you have a budget hardtail or suspension bike and damage the rotor and need a replacement, you can go far wrong with Clarks Lightweight Stainless Steel Floating rotor. It’s made from a slightly cheaper grade of stainless steel and the carrier is painted rather than anodised but it’s available in 160, 180 and 203mm and 6-bolt pattern.
In theory the floating design has all the benefits mentioned previously, but the heat dissipation is not quite as good, and it can ding a bit too easily, but it is an absolute bargain.
How we test
When testing a disc brake, we always run the stock rotors simply because the brake is designed to use them. We run the same size rotor front and rear and obviously record the weight with that size. We’re equally consistent when it comes to evaluating power, bite and feel of the brake, undertaking repeat stops using the same bike, tyre and tyre are pressure. During testing we gauge the straightness of the rotor and fit it to several different hubs to check tolerances, and compatibility.
Are disc rotors all the same?
Essentially there are two types of disc rotors – one piece and two-piece. The former is the most common and is simply a circular piece of stainless steel with all the mounting holes, etc machined into the surface. As the name suggests, a two-piece rotor consists of a carrier, usually aluminium, and stainless-steel braking surface. The reason for the aluminium component is it’s lighter, stiffer and the also acts as a heat sink.
Both one and two-piece designs are interchangeable, although you generally see the latter on more expensive disc brakes.
How are disc rotors made?
The majority of one-piece disc rotors are laser cut from stainless-steel. This blank is then heat treated to make it harder and maximise its corrosion resistance, before being ground totally flat (straight). On a two-piece design the attached braking surface is made in the same way and the alloy carrier is also CNC machined. The parts are usually with riveted together.
Shimano’s Ice-Tech rotors look similar to regular rotors, but they have a slightly different internal construction. The company describes it as a ‘clad’ rotor and that means it has an aluminium core, sandwiched between two stainless-steel braking surfaces. The aluminium is lighter and better at absorbing heat, which can reduce brake fade.
Why are rotors stainless steel?
It’s naturally corrosion and heat resistant, two things you want with any brake system that’s exposed to the elements.
Do mountain bike brake rotors come in different sizes?
The most common rotor sizes are 160, 180 and 200mm, although we’re starting to see bigger 220/225mm rotors for eBike use. There’s more mechanical advantage with a bigger diameter rotor, so greater stopping power but obviously more weight too.
Although most manufacturers have a 200mm option, Shimano offers a 203mm, which we think is a bit of throwback to when rotors were measured in inches (203mm is actually 8in) but this is not consistent because a 160mm rotor is 6 1/4in for example. To some degree it doesn’t really matter because if you use the right adapter any caliper will work with any rotor. Third party brake manufacturers are also pretty good at offering most sizes – Hope for example offers 200, 203, 205, 220 and 225mm rotors.
What is a floating rotor?
This is where the stainless-steel braking surface is not joined to the aluminium carrier but is allowed to ‘float.’ When the rotor heats up the rivets allows for a certain amount of expansion and also mean the braking surface won’t warp. This design also heats up a lot quicker, which is good because brakes and pads have an optimum operating temperature, so the sooner they reach that the better.
What is a vented rotor?
Hope is one of the few brake manufacturers to make a vented rotor. It uses a similar carrier to a floating rotor, the difference is the braking surface is made from three layers of stainless, which are joined using a vacuum brazing process. Internal fins help channel air around the braking surface and Hope claims this can reduce heat build-up by 15%.
Vented rotors do weigh a lot more, and you will need a dedicated caliper to run them.
Why are rotors different thicknesses?
It’s all about stiffness. A bigger disc is more flexible, so more mass adds rigidity. Again, it adds weight but we figure if you need this much brake power, we suspect you’re going to be less concerned about that anyway.
How do disc rotors attach to the hub?
Either via 6-bolt or Center Lock. As the name suggests, six-bolt rotors come with six small Torx or hex fasteners that let you tie the rotor to the hub. Center Lock has a splined interface and uses a lock-ring to hold the rotor in place. Adapters available to convert one to another.