These standards centre around maintaining brake fluid performance in a range of temperatures (high and low) and also specify the minimum boiling temperatures which the fluid manufacturers must adhere to. Inhibitors, to prevent corrosion and oxidisation.ĭOT brake fluid is required to meet strict standards and specifications set out by the Society of Automotive Engineers and the Department of Transportation (DOT) - hence the name.A modifier-coupler, which changes the amount of swelling of exposed rubber parts.A solvent diluent, usually glycol ether, which determines the fluid's boiling point and viscosity and accounts for 50-80% of the fluid.A lubricant, such as polythene or polypropylene, to keep parts moving freely - 20-40%.These substances can be broken down into four key components: Glycol-based fluids consist of a mixture of ingredients with as many as ten separate substances making up the final product. All DOT fluids (with the exception of DOT 5) are made up of a poly-glycol base. There are two types of brake fluid used in hydraulic mountain bike brakes today:Ĭertainly the most commonly used brake fluid in use today, due to its wide use in the automotive industry, is DOT fluid. The brake fluid also has to resist, as far as possible, the high temperatures created by the braking forces. This is possible as fluids are generally incompressible. Its job is to transfer the input forces you create at the master cylinder (lever) to the caliper pistons. If you've read How Hydraulic Brakes Work you will know that brakes slow us down by turning kinetic energy into heat by using friction.īrake fluid is only one of several vital components which enable hydraulic brake systems to work effectively. I'll explore these brake fluids in detail, sum up their advantages and disadvantages and explain why the experts believe their choice of fluid is best for us riders. Well we're going to try and answer those questions today. But which brake fluid is best and why do we have two to begin with? Most of you will know that hydraulic brakes are designed to use one of two main types of brake fluid - DOT fluid or Mineral Oil, and which one you pick is not a choice made by you or me, but rather by the brake manufacturers themselves. One of the great debates and areas of confusion surrounding brake fluid is which brake fluid is superior? Without it, or without enough if it, the forces you apply at the brake lever would not be transferred to the caliper, pads and rotor. Brake fluid is an essential part of the hydraulic braking system.

Dot 3 brake fluid color chart