How to Choose the Right Disc for Your bike?

Introduction

The disc is a bicycle part installed on the wheel hub, used to provide braking force in the disc brake system. The size of the disc varies to suit different terrains and riding habits. The simplest discs are made by stamping stainless steel, and more expensive ones have complex internal structures to improve braking performance and reduce weight. The two common ways of installing discs are center lock and six-bolt. In this article, we will list the main things you need to know about discs, to help readers choose the products they need.

What is a disc?

A disc is a metal disc mounted on the hub, which is the main contact surface of the caliper brake. Different sizes and designs can be used for different purposes, some prioritize providing maximum braking force, some prioritize generating minimal heat, and some aim to reduce weight.

Size of the disc

The role of the disc is to slow down the tendency of the wheel group to rotate, using the caliper to squeeze the disc to generate friction. This generates heat, the larger the disc, the more heat is absorbed by the disc, and the smaller the disc, the easier it is to overheat and produce thermal exhaustion, causing a significant drop or even disappearance of braking force. Simply put, the larger the disc, the better the braking effect. However, not all vehicles and riders need maximum braking force, in many cases, finding a balance between braking power, brake feel, and lightweight is very important.

Typical road bikes and cyclocross bikes use 140-160 mm discs, which are not only powerful but also light; mountain bikes generally use 180-220 mm discs. Many mountain bikes adopt a "larger front and smaller rear" combination, such as a 200 mm disc for the front wheel and 180 mm for the rear wheel; downhill bikes now also use discs over 200 mm, as do electric assist bikes.

Disc design and material

Most discs are made of high-quality stainless steel, which is not only sturdy and durable on the braking surface but also usable in all weather conditions. The disc surface has many hollows, which help water, mud, and small debris fall off quickly. These designed and reasonably arranged holes can also reduce weight.

A major design principle of the disc is heat dissipation, and there are many ways to achieve this demand. Some discs are coated with heat-dissipating materials on the inner ring of the disc, some like SRAM's latest mountain disc increase thickness for heat dissipation, and some learn from motorcycle discs to connect a stainless steel outer ring to an aluminum alloy inner ring. This design claims to accelerate heat dissipation while being lighter. Shimano's IceTech is to sandwich a layer of aluminum between two layers of stainless steel to speed up heat dissipation.

Installation standards: Center lock vs six-bolt

For strong braking, installation must be firm. The two common ways of installing discs are center lock and six-bolt. The latter is the most common, using six screws to screw the disc onto the hub, which is not only light but also simple in structure, just need hands. The other is the center lock, first put the disc on the specific position of the hub, and then screw on the cap, here you need to use specific tools.

How often to change

Like brake pads, discs are consumables, each time you squeeze the brake, it will wear a little bit, and over the years, it needs to be replaced. The sign to determine the timing of replacement is the thickness of the disc, Shimano suggests that if a 1.8 mm thick disc has been worn to less than 1.5 mm, it should be replaced urgently; SRAM suggests that if more than 0.3 mm has been worn off, it should be replaced urgently, or if the thickness is already less than the amount indicated on the disc surface.

How do I know which one to buy

When buying a disc, remember a few things:

• Buy a disc of the same brand as your caliper unless you are specifically retrofitting;
• Buy a disc type compatible with your wheelset, check whether it is center lock or six-bolt;
• See how big a disc your frame and fork can accommodate;
• See how much braking power you need, if you always can't stop before, then buy a bigger one this time.