Which size rotors for disc brakes

The ability of a light lever squeeze to enact huge braking forces at the wheels, is one of the most impressive mechanical features in mountain biking. We tend to take our brake specification for granted, until there is fade or horrible squeal, on a long descent.

But should you actively be rethinking your brake rotors in terms of size? Shimano mountain bike brakes range overview. SRAM mountain bike brakes range overview.

Why are brakes still steel and not carbon-fibre? The simplest brake upgrade, to gain sheer stopping power, is upsizing rotor size. You can exchange brake pads, experimenting with different material compounds for feel and durability, but rotor size has a much more significant influence on absolute brake performance.

Before discussing the merits and debits of large brake rotors , a quick mechanical engineering recap about what mountain bike disc brakes do. To slow your bike down, you need to convert its rolling momentum into a different kind of energy. Look between the pads for a wobble, or a gap opening and closing. If you see either, the rotor is out of true.

Often, but not always, warped rotors can simply be bent back using a rotor truing tool like the Jagwire Disc Brake Multi-Tool. Note the section that needs truing, and rotate it away from the caliper.

Gently work the tool around the rotor at that section to straighten it. This only works if the rotor is rubbing in one specific spot. Rotors are strong stoppers, but are fragile side-to-side. Rotors also need to be replaced when the total thickness of the braking surface is less than 1. Brake pads are found inside the calipers. There are two main types of brake pads. Resin brake pads also called organic are composed of organic materials like glass, rubber, and fibrous binders bonded together with resin.

Sintered brake pads also known as metallic are made of metallic grains that are bonded together at high pressure. In terms of feel, resin pads are quieter and have a stronger sense of bite. They also wear more quickly, particularly in muddy conditions. Sintered pads are the choice for riders who do mostly steep, lift-served mountain biking.

They produce more heat but are less susceptible to its effects; and they last longer under heavy use and in wet conditions. Detach the wheel and use isopropyl alcohol on a clean rag to wipe off the rotor, then remove the pads and clean them as well. Make sure to let the pads dry completely before reinstalling. SRAM recommends replacing pads when the total thickness of the backing plate and the pad material is under 3mm.

Shimano says that when the pad material alone is less than half a millimeter thick, it needs to be replaced. Opt for a minimum of grit sandpaper. The more common sizes include mm, about 6 inches, which is one of the smaller versions; mm; mm; and mm. The most common large size is mm, which is 8 inches. Disc brake dimensions refer to the size of the rotor, which is the disc in the disc-braking system.

The bike frame and rotor diameter must be compatible but can have some variance in size as long as the disc-specific hub is compatible with the rotor. Disc brakes are often used on mountain bikes because they are not affected by water or mud. They perform better on rugged terrain and other extreme road conditions because they are located in the middle of the wheel and not on the rim. The downside to disc brakes is they are heavier than rim or V-brakes.

Disc brakes are also more expensive. Most mountain bikers prefer larger disc brake sizes because they offer more stopping power. This is important for steep downhill runs and the extra workout braking systems get on mountain terrain. Mountain bike disc brake sizes typically run about mm.