The Science Behind Hydraulic Disc Brakes

When you pull the brake lever on a hydraulic system, brake fluid is pushed down the hose towards the calliper. The pistons are pushed out towards the rotor and press the pads against it, stopping the bike. The type of brake fluid, piston size and rotor size are therefore the main features of the system and differences in these specifications can aid performance.

Brake Fluid

Use only the fluid specified for the exact brake model. DOT fluid and mineral oil systems use different seals and must never be mixed or converted by changing fluid. Both types are used in demanding riding; performance depends on the complete brake design. Follow the manufacturer’s fluid type and service interval.

Pistons

Two piston callipers have a piston on each side of the calliper and four piston systems have two pistons on each side. Total piston area and lever geometry determine clamping force. Four piston calipers often use larger pads to distribute load and heat, but pad area alone does not determine braking torque. Friction, clamping force and rotor radius also matter.

Rotor

A larger rotor has a larger brake surface area and can keep brakes running at a more optimal temperature. However, simply using the largest rotor possible isn’t necessarily going to increase brake performance. Variables such as braking intensity, braking duration and rider weight build heat between the pad and the rotor. Too hot or not hot enough could lead to a reduction in the control the rider has over braking power. Brakes that get too hot during use could be helped by an increase in size of rotor. Brakes that don’t heat up enough to create optimal friction could benefit from a smaller rotor. The colour of the spokes of the rotor shows the effect of heat dissipating down the material. When it looks brown, heat is generally being dissipated well. If it is purple, this shows a scorching effect.

What this all means is the specification for your bike brakes really comes down to several main variables your weight, the way you ride it and how aggressively you use the brakes, the type of terrain and conditions you like to ride in and how often you are expecting to use your bike.

Our other article, Brake Tuning and Setup, details how the brake system you have is set up for the individual rider and covers brake pad options, all of which you will find available to buy in our wide range of products in the online shop.