There are several types of motorbike brake fluids, and the choice of the correct type depends on the specifications of the motorbike manufacturer and the brake system used. The two main types of brake fluid commonly used on motorbikes are DOT (Department of Transportation) specification brake fluid and ISO (International Organization for Standardization) specification fluid.
DOT 3, DOT 4, DOT 5, and DOT 5.1:
These specifications are set by the U.S. Department of Transportation and are common on motorbikes manufactured in North America. DOT 3, DOT 4 and DOT 5.1 fluids are glycol based and are hygroscopic (moisture absorbing). DOT 5, on the other hand, is silicone based and non-hygroscopic. DOT 5 fluids do not mix well with DOT 3, DOT 4 or DOT 5.1 fluids, and are generally not recommended for conventional brake systems.
ISO 4925:
That is, this is a standard set by ISO and is common on motorbikes manufactured in Europe and some Japanese motorbikes. Like DOT fluids, ISO specification brake fluids are glycol based.
It is also essential to follow the motorbike manufacturer's recommendations and use the specific type of brake fluid listed in the owner's manual. Incorrectly mixed brake fluids can adversely affect brake system performance and compromise safety.
Also, be aware of the boiling point of the brake fluid, as higher quality fluids tend to have higher boiling points, which is beneficial under heavy braking conditions.
It is always advisable to check your bike's owner's manual and, if in doubt, seek the guidance of a professional mechanic to ensure you use the correct type and keep your brake system in optimum condition.