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Brakes are brakes aren’t they? Some kind of caliper with brake pads that grips the wheel to make the bike stop when you pull on the brake levers. Right? Wrong!!! That’s certainly what I had on all my bikes growing up. Simple little rim brakes that did the job. 
 
But today…? the lingo is rotors, disc brakes, hydraulics, special fluid. The kind of stuff you get your car mechanic to look at when you service your car.

So the big in-thing we’re talking about is disc brakes – the be all and end all of bike braking systems according to one camp and an unnecessary expense cooked up by the cycling industry to squeeze more money from the cycling community according to the other camp.

close up of two piece disc brake and caliper on bicycle wheel
Whatever the argument, it looks like disc brakes are here to stay until the next big thing comes along.
 
So for newbies and die-hards who still favor the simple traditional rim brakes let’s look at the 7 important things you need to know about disc brakes and see what all the hullabaloo is about. 

1. So What Are Disc Brakes?

Disc brakes – have three main components to them 
1. A metal disc known as a rotor which is fitted to the middle of the wheel 
2. A caliper which is attached to the frame or fork. Inside the caliper are a pair of pistons which fit either side of the rotor
3. A pair of brake pads which are fitted into the caliper pistons. 

2. Types of Disc Braking System

There are two types of disc braking system 
  1. Pulling the brake levers which are attached to cables – like traditional rim brakes – squeezes the calipers which force the brake pads to grip the rotor making the bike wheel stop. This method is known as mechanical.
  2. Pulling the brake levers builds up a pressure which forces fluid to move through a solidly sealed line into the caliper which presses the pads against the disc making the bike wheel stop. This is known as a hydraulic braking system.

3. Hydraulics versus Mechanical Disk Brakes

Mechanical brakes are very easy to look after. Just like with rim brakes the brake levers are quick and easy to adjust either directly on the levers or on the caliper itself. A common complaint though is that because you are pulling on the cable, you need to apply more pressure on the brake lever to get the bike to stop. They are significantly cheaper than hydraulic braking systems and therefore will be found on cheaper retail electric bikes.
 

Hydraulics are seen as far superior to mechanical brakes by many in the biking world. One reason for this is that rather than pulling on a cable you are pushing the hydraulic fluid towards the calipers. This means less effort is required compared to mechanicals.

In fact the brake lever action is so light that there are brake levers that require the use of only one or two fingers like this one. They also offer better modulation ie precise control on how much the brakes bite the rotor.

The other key advantage is that the brake pads become self-adjusting as they wear down because of the fluid pressure. Hydraulic braking systems are much more expensive and can be found on more high-end eBikes.

The disadvantages of hydraulic brake systems are that they require more maintenance which can be long-winded, potentially messy and more expensive.
 
You need a special bleeding kit so that the old fluid can be flushed out of the system and replaced with new fluid.
 
It is not as easy a DIY job as adjusting mechanical braking systems and many experts suggest you take your bike to a mechanic for servicing.
 
The brakes can feel spongy if not looked after properly. This sponginess is usually related to trapped air in the system so requiring more bleeding outside of its servicing time.

4. Disc Sizes

The discs ie the brake rotors come in various sizes ranging from 140mm up to 203mm. The larger the rotor the better the braking power.
Below is a table that shows the typical sizes of rotors for specific types of riding.
 
Road / Cyclocross Mountain Enduro / Downhill
140mm 160mm 200mm
160mm 170mm 203mm
180mm
The most common sizes are 160mm, 180mm, and 203mm.
 
Most of these sizes can be run with either brake system but you’ll need an adapter for your fork or frame.  Basically specifically sized brackets to go with the appropriate sized rotor.
 
The bigger the size of the rotor the heavier it is but the better it is at dissipating heat and therefore giving better braking power.

5. Types of Rotors

There are two main types of rotor
 
The most common comes as a standard one piece made from stainless steel. You also get a few made from titanium titanium disc brake for bicyclelike this one
 
 
Stainless steel one piece rotors are fairly lightweight and reasonably long-lasting. With heat buildup they can warp or get easily damaged in a crash. They also tend to get quite hot as there’s no other metal to transfer the heat to. This means the braking power tapers off after a long descent.
 
But for normal riding they do the job and still have better braking power than rim brakes.

The second type of disc is the two-piece rotor with a steel braking surface and aluminium carrier like this SRAM Centerline XR rotor SRAM centerline 2 piece 6 bolt rotor for bicyclefrom Amazon or the Hope Floating rotor from JensonUSA

They are generally more expensive than a one piece rotor because of the materials used and their overall superior braking power. The two piece rotor allows the steel to pass on the heat via the inner aluminium part.

This is what makes them better at dissipating heat and cooling down the rotor which gives the better braking performance. They are still lightweight but will stay truer for longer.

6. How are disc brakes better than rim brakes?

Disc brakes have faster and superior braking power in the wet, mud and snow compared to rim brakes.
 
This is partially because of their placement on the wheel which has a higher clearance from the ground and also the design of the rotor itself – almost mesh like with lots of gaps. So water can literally pass through the rotor and their height from the ground means that they are less likely to get covered in mud and other debris.
 
Also because of their size compared to that of the wheel itself, it’s much much quicker to disperse of any water on the disc so giving significantly faster braking grip.
 
Rim brakes on the other hand take a much longer time to brake in the wet as the brake pads have to dissipate the water on the rims before getting a good grip on the wheel. Simply due to the size of the wheel it will take slightly longer for the brakes to get a good grip in the wet.
 

7. Installing Discs

The fitting of the rotor will either be via a central spline which needs a cassette lockring tool or via 6 bolts. Center lock rotors are two piece discs and therefore tend to stay truer than 6 bolts discs which are cheaper and more easily available. Both types come in all standard sizes. 

With the center lock you get two different kinds of lock rings i) an internal ring which goes on the inside – looks similar to a cassette lock ring. You use a cassette lock ring tool to install it, or ii) an external ring for which you need a bottom bracket tool. 

6 bolt rotors are very easy to install. The bolts should be tightened in a mesh/zigzag pattern to ensure even balancing of the rotor against the hub. 

If your existing bike has rim brakes you won’t be able to just buy and fit a disc brake kit on your wheels. You will need to buy a wheel that has a rotor mount built in.

centerlock adapter for bicycle disc brake

A center lock wheel can be adapted for a 6 bolt disc with a base spline for mounting on to hub, pins that go into the base spline via the rotor and a lock ring goes on top. A 6 bolt hub cannot be adapted for a centerlock wheel.

Summary

So in summary it seems disc brakes are here to stay. Manufacturers are producing increasing number of regular bikes and electric bikes with mechanical or hydraulic disc brakes. And while rim brakes are not going to disappear overnight, we might as well accept and maybe welcome the advent of the disc brake.

They are fairly lightweight, more efficient braking systems compared to rim brakes and can be used in all weather conditions. But like everything there are pros and cons. Hopefully after reading through the 7 important things you need to know about disc brakes,  that you’re in a better position to make the right choice for you.

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