While a racer will need to change their brake fluid far more regularly due to constantly getting it very hot, the average road rider need only stick to the manufacturer’s recommended intervals. Brake fluid is ‘hygroscopic’, which means it loves to absorb moisture from the air; as water boils at 100°C, the more of it is in your brake fluid, the more spongy the brakes will feel, and ultimately the more likely they are to fade when used hard. As this absorption happens over time, it’s important to change the fluid at the specified times.
Most bikes use a DOT 4 fluid – a standard set by the Department of Transportation for minimum specifications. There are two boiling points; dry and wet. Dry is the boiling point of the fluid when it’s brand new; wet is the boiling point after it’s been in the system for a while, and has absorbed 3.7% of its volume in water.
DOT 5.1 is a glycol-based fluid that is compatible with DOT 4 fluid, and simply boils at a higher temperature. Don’t confuse it with DOT 5, which has the same higher boiling point, but is silicone-based, and must NOT be mixed with glycol-based fluids.
Brake fluid can typically be changed on a new bike equipped with ABS in just the same way as an older machine, but it’s very important that air is not allowed to enter the system during the process – if it does, you’ll definitely need to bleed the system carefully.
The general rule on most motorcycles is to have front and rear brake fluid changed every two years. The hydraulic clutch on many bikes use similar brake fluids or mineral oil, which should also be replaced every two years.
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