Why did SRAM choose DOT 5.1 over mineral oil?

We specifically choose DOT fluid for its performance characteristics:

  1. Heat/moisture management: DOT fluid manages heat better. While pure mineral oil and pure DOT fluid both have boiling points around 280C, DOT fluid is much better at managing water, which, over time, always finds its way into any brake system. DOT fluid makes any water in the system part of the fluid, while mineral oil pushes water to the edges. If a fair amount of water migrates into a mineral oil system, water’s boiling point, 100C, becomes that of the system. Our tests showed that even old, “wet” DOT fluid the boiling point never gets below 180C, while a bike brake system rarely sees temperatures over this point. The result: DOT fluid offers more consistent braking performance.
  2. Feel: DOT fluid is less compressible than mineral oil. DOT was specifically invented to be incompressible—a key attribute of any high-performance hydraulic fluid.
  3. Serviceability: Both mineral oil and DOT fluid systems require regular service. Both fluids must be handled the same way: wear gloves, collect your waste fluid, and recycle it appropriately. DOT fluid offers some advantages: For example, DOT refers to the United States Department of Transportation, which means the fluid must meet a common set of standards set by this regulatory agency. DOT fluid can also be cleaned up with water, no solvents required.

DOT summary:

  • DOT fluid is brake fluid – it gives you great performance
  • DOT fluid manages water – any sealed system will have water migrate in
  • DOT fluid and mineral oil must be handled in the same way: Mechanics should wear gloves and properly dispose of it.