Tuesday, 19 August 2014

Buyer's guide - Mountain bike disc brakes explained

Mountain bike hydraulic disc brakes are very simple in principle. There is a lever attached to a master cylinder at one end, a hose in the middle and finally a calliper pushing some pads on to a metal disc bolted to your wheel hub. Tiny changes to the brake system can make a noticeable difference to how well it performs, so let´s see which are the main parts of your mountain bike disc brake system.

Lever/master cylinder
All disc brakes have a master cylinder (brake lever body) with a piston inside pushed by the brake lever, but on some brakes the piston is parallel to the handlebar (e.g. Shimano Deore), while on others like in Formula´s it’s perpendicular to it. The master cylinder contains the brake fluid reservoir allowing to automatically adjusting for pad wear and heat expansion of braking fluid. Brake levers can be very different in shape and material (aluminium, carbon fibre) and designed for one finger use, two fingers or more. Potential adjustments include reach, leverage ratio and bite point.

Mountain bike brake parts
Mountain bike lever/master cylinder parts - Hope Tech3 V4

Master cylinder orientations in mountain bike disc brakes
Different master cylinder orientations in Hayes Prime and Radar models

Reach adjustment
This adjustment allows you to move the lever relative to the handlebar to find the most comfortable position for your fingers. Tool-free adjustment is standard in some models from the main brake manufacturers like Shimano, Avid, Formula, Magura or Hope, and for the rest is normally via a small bolt close to the brake lever.

Reach adjustment
Reach adjustment in Formula The One and Magura MT7 brakes

Bite point / Free stroke adjustment
Using this adjustment, the amount of lever travel before brake activation can be changed, effectively making the pads feel closer to the rotor. Is also known with different copyrighted names depending on the brake manufacturer (Contact Point Adjust on Avid brakes, or Free Stroke on Shimano´s), but this feature always allows you to make the brake feel firmer and faster. This adjustment it´s often with a small bolt, but there are also brake models with tool-free adjusters.

Bite point - free stroke adjustment
Bite point / free stroke adjustment in Shimano Saint and Magura MT8 brakes

This part of the brake system includes the pistons and pads that are pushed on to the brake rotor to slow you down. Although there are brake manufacturers offering 6-pot or 8-pot callipers for MTB,  widely used callipers have two-piston (two-pot), using two opposing pistons, or four-piston (four-pot) with two pistons each side and bigger pads offering extra stopping power normally for enduro/gravity/DH riders.

2-pot and 4-pot mtb callipers
Magura MT8 (2-pot) and Hope Tech 3 V4 (4-pot) callipers

Some callipers are cast/forged from one piece of metal, offering typically a better stiffness and a firmer braking feel, while others are manufactured from two sides bolted together.

One piece forged and two piece bolted mtb callipers
Shimano XTR one piece forged calliper and Shimano Zee two piece bolted calliper

The callipers are always attached with two bolts, and two different mounting standards are mainly available in the market, International Standard mount (IS) and Post Mount (PM). Nowadays the Post Mount is almost the universal choice by mountain bike brake manufacturers and the IS mount is becoming less popular and used only for bike frames.

IS mount and Post Mount mountain bike brake attachments
Old Shimano XTR IS mount calliper and New Shimano XT Post Mount calliper  

If you wish to install bigger disc brake rotors or change your mounting type, there are different disc brake mount adaptors available depending on the rotor size and attachment mounting.

Most mountain bike brake manufacturers recommend that you replace the brake pads with genuine branded replacements. Typically the genuine pads offer a good compromise between performance and lifespan, but there are several third-party manufacturers that sell alternatives, some of them at a much lower price and others with improved performance or quality.

Different mtb brake pad compounds
Different mountain bike brake pad compounds

When you replace your brake pads they are basically three different materials, depending on your riding requirements. Full sintered metal brake pads, semi-metallic pads and organic pads (also known as resin). All the differences are widely explained in a previous article here.

Can I upgrade pads? Yes! Organic pads are popular standard fitments, as they are quiet and have a good initial bite, but they fade when warm and can fail completely with extreme heat. Full metal sintered pads offer slightly less friction and initial bite and can be very noisy, but stay consistent at all temperatures and last longer. Combining the best from both worlds are the semi-metallic brake pads, with an organic core with embedded metal particles. They work as good an the organic pads from cold with good initial bite, and have an increased lifespan and hot performance due to the added metallic particles.

Mountain bike disc rotors are either made from a single piece of stainless steel or they are a two-piece design consisting of an alloy carrier with a steel braking surface. Using this two-piece design, the braking surface is smaller and less likely to warp or get damaged when hot, and the rotor weight can be reduced. Shimano Ice Tech rotors are a bit different sandwiching an aluminium core between the two stainless steel braking surfaces (Shimano Ice Tech rotors review).

Single piece steel and two piece aluminium-steel mtb rotors
Avid single piece stainless steel and two piece aluminium-steel HOPE rotors

Disc rotors are available in several sizes, often 140, 160, 170, 180 and 200mm. A bigger disc means more leverage and more power. Brake power grows by roughly 20 per cent for every 20mm increase in diameter.

The common 180mm front/160mm rear combination is a great compromise for trail and cross-country, but you can go as small as 140mm or as large as 220mm. These extremes are rare and 203mm is the biggest common size.

They are two types of rotor fixing systems commonly used on the market today; IS (International Standard) 6-bolt (widespread use) and Center Lock (Shimano proprietary).

  • IS 6 Bolt  - The most common mountain bike rotor fixing system in use today with six fixing bolts. Using this fixing system you always have the risk of stripping a thread on fixing bolts and hub mounting points, so is better to be careful when installing this type of disc rotors.                                                                                                                                                                                                  
  • Center Lock - Shimano Center Lock system eliminates the bolts and therefore the risk of stripping threads, using only a centre locking ring. Installation is very easy but a Center Lock wrench is needed. Due to the low mass-market adoption the hub choices are limited.

Different mountain bike rotor fixing systems
Main mountain bike rotor fixing systems used today (Shimano XT and Shimano XTR)

Please Like, Tweet or +1 this guide and help your friends to better understand mountain bike disc brakes, and remember that you can greatly improve the braking performance of your mountain bike brake system only upgrading your brake pads.

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Choose your semi-metallic high performance mountain bike brake pads Made in Japan  at www.rahoxbrakes.com

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