Buying the best mountain bike disc brake rotors are not the first thing that pops into many riders minds when it comes to MTB upgrades, but a new set of rotors can mean less weight, less noise and more braking power — plus they are a relatively inexpensive upgrade.
How to decide if you need new rotors?
Beyond just an upgrade to something lighter or larger, rotors wear out over time. Many discs will have a minimum thickness printed somewhere on the rotor — you'll need a set of calipers to measure. If your rotors don't specify a minimum breadth, measure the thickness of the braking surface and compare it to an area the pads don't touch; if there is a difference of 2/10-3/10 of a millimetre your rotor is worn and it's time for a new one.
If you don't have a set of calipers to measure, take a pick or a paperclip and run it along the rotor; if the pick gets caught up on an edge at the bottom of the braking surface, it might be time for a new disc.
Badly bent rotor?
Rotors are surprisingly fragile, and it doesn't take much to knock one out of true — extreme heat from dragging your brakes all the way down a descent can also warp discs. More often than not a few minutes with a truing tool and you can silence a disc that pings a brake pad as the wheel spins, but rotors can become deformed past the point of no return. If you're wrenching away at a disc for more than ten minutes and it's showing no signs of improvement, it's time for a new one.
How to buy new mountain bike rotors
1. How to buy MTB rotors: size
Rotors come in 140mm, 160mm 180mm and 203mm sizes, and depending on the category of bike you're riding, it will be set up for a different size disc — the front rotor will usually be a size up from the rear. XC bikes will often have a 160mm rotor in the front, trail and enduro bikes will jump up to 180mm and downhill bikes will have a 200mm+ pie plate. The size of your new rotor will have a drastic impact on braking power. If you're looking for a bit of added power consider going a size up; however, you'll likely need a mount-to-caliper-adaptor to make up the space.
On the other hand, larger rotors are heavier, the adaptors create another piece to come out of alignment and they are more exposed to trail hazards. Some fork manufacturers also advise against using rotors larger than 180mm on their short travel mountain bike forks.
2. How to buy MTB rotors: mounts
The hubs on your wheels will determine whether you need a six-bolt or centre lock rotor. Centre lock rotors are secured to the hub with a lock ring while six-bolt rotors use, you guessed it, six Torx bolts.
Centre lock rotors are quicker to install and remove, but usually, a touch heavier while the hubs save a few grams.
3. How to buy MTB rotors: floating or fixed?
Floating rotors sees the steel disc mounted to an aluminium carrier, a technology borrowed from motorbikes. Floating rotors are claimed to offer better heat dissipation and improved warping resistance, but the real benefit is they are always lighter than non-floating designs.
4. How to buy MTB rotors: brake pads
The debate over sintered vs organic pads is hotly contested, and we're not going to get into that here, but when bolting a new set of rotors onto your wheels take note if 'resin only' is printed anywhere on the disc. Usually only affecting rotors on the lower end of the price spectrum, metallic pads will chew up resin-only discs, and may even cause them to overheat and buckle.
SRAM's CenterLine rotors aren't a fancy two-piece design, and they can be a bit noisy; though not as bad as the gobble-gobble Avid discs of yesteryear. Now available as a six-bolt mount and centre lock, the CenterLine Rotors feature a 12-spoke design which stands up well to warping and features a rounded edge.
Available in sizes from 140mm all the way up to 220, the all-steel rotors are simple but effective stoppers — and you can usually find them on sale too.
Shimano's Ice Tech rotors are some of the fastest stopping and most reliable discs you can buy. The centre lock XT RT MT-8000 discs feature the brand's Ice Tech construction which sees an aluminium core sandwiched between a steel exterior. This design cuts a small amount of weight and allows the rotor to manage heat better than a full steel rotor.
Built around an aluminium carrier the MT-8000 rotors see a tapered fin along the inner edge to help draw heat away from the braking surface and expedite heat dissipation. The only difference between the XT and more expensive XTR rotors is a bit of heat-dissipating paint.
Only available in larger diameters, Hayse's D-Series rotors are designed for power. At 1.95mm thick, the rotor can absorb and dissipate heat more efficiently under braking to keep stopping more consistent as the temperature builds.
With the D-Series Rotor, Hayse introduced what it calls Modal Resonance Cancellation; a fancy way of saying the brand worked out when a rotor and pad begin to resonate and designed them to work together to cancel this vibration out — in short, they shouldn't howl. Hayse also employed what it calls QuickBite2, so the rotors bend fast and distribute pad material evenly into the friction tracks.
For the most part, rotors are silver on silver, or silver on black, i.e. boring. So leave it to Hope to add a splash of colour with anodized carriers on its Floating Disc Rotor. The aluminium carrier is CNC machined and riveted to a laser-cut steel disc; everything is made in Hope's Barnoldswick, UK facility.
With a two piece design, Hope say the Floating Disc rotor will resist warping under extreme heat and the perforated rotor does well to clear muck. With the carrier and rivets extending out nearly to the braking surface, Hope warns that the Floating Disc may run into clearance issues with some brake and fork/frame combos.
In 2015 the engineers at SwissStop started tinkering with disc rotors looking at heat transfer and structure to find the best possible balance between temperature dissipation, strength and while still keeping the disc light on the scale. They lab-tested a range of discs, then designed digital algorithms based on what they learned to test a range of models to simulate heat, different structures and airflow.
The result is the Catalyst Disc Rotor. With a two-piece design consisting of a 7075-T6 aluminium spider, Swiss Side chose SUS410 stainless steel for the brake track for its weight and thermal management properties. Swiss Side also designed the geometry of the brake track area to minimize vibrations and shuddering.
Galfer is well known in the powersports industry, providing OEM stock for quite a few motorcycle brands, and the Spanish outfit has also applied their stopping power expertise to MTBs. The Wave rotor is laser-cut and double-disc ground from high carbon stainless steel for durability and to ensure either side of the disc is actually parallel.
The rotors boast an anti-corrosion and heat treatment for more consistent braking along with temperature management and dissipation to prevent warping.
TRP's two-piece rotors feature a traditional floating design with a steel braking surface wrapped around an aluminium carrier. The carrier and rivets are machined to be flush with the rest of the rotor to prevent the clearance issues some other two-piece rotors rub up against.
The braking surface features six recessed slots to allow water, mud, and other trail debris trapped between the pad and rotor an escape route — they also serve as a good wear indicator too. Available in sizes from 140-203mm, the TRP 2-piece rotors are only available with a centre lock mount, just make sure you hang onto the lock ring from your previous rotors.
Disc rotors are unsprung rotating mass, meaning it is at least three times harder to accelerate than non-rotating mass — it's pretty close to the hub. To every weight weenies delight, the Magura Storm SL.2 6-Bolt Rotor tips the scales at just 143g in a 180mm diameter.
For such a lightweight rotor they have a wider brake surface which helps to stop the pads from tipping and increases modulation — plus they look great. However, with so many cutouts, they chew through pads pretty quickly, and they are only available in 160mm and 180mm diameters.