Know Your... Break Fluids

We caught up with the brains over at Motul to see what the deal is with brake fluid, why you should use the best and how it works to make your bike stop… faster!

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FB: What is the purpose of brake fluid?

TM: To stop you! Brake fluid is what transfers the action from your brake lever to the discs via fluid pressure. When you pull the brake lever, you’re moving a piston in the brake master cylinder. This pushes the brake fluid all the way down towards the wheels, and at the wheels are calipers. These calipers also have pistons that the fluid now presses on and squeezes the brake pads tight against the brake discs.

FB: What is it made from?

TM: All DOT fluids (with the exception of DOT 5) are made up of a poly-glycol base. Glycol-based fluids consist of a mixture of ingredients with as many as 10 separate substances making up the final product. These substances can be broken down into four key components: 20-40% is a lubricant – such as polythene or polypropylene, to keep parts moving freely. 50-80% is a solvent diluent – usually glycol ether, which determines the fluid's boiling point and viscosity. Then the small remainder is a made of a modifier-coupler – which changes the amount of swelling of exposed rubber parts, and inhibitors – to prevent corrosion and oxidisation. DOT brake fluid is required to meet strict standards and specifications set out by the Society of Automotive Engineers and the Department of Transportation (DOT), which is why it’s called DOT. These standards centre around maintaining brake fluid performance in a range of temperatures (high and low) and specify the minimum boiling temperatures which the fluid manufacturers must adhere to.

FB: Does brake fluid have an expiry date?