How often to bleed hydraulic brakes, and why the fluid decides
The interval is not a property of the brake. It is a property of what is inside it.
Last updated: 2026-08-21
Two fluids, two behaviours
DOT fluid is hygroscopic: it absorbs water out of the air over time, and water lowers the boiling point of the fluid in the part of the system that gets hottest. That is why SRAM specifies an annual bleed for DOT systems regardless of how much you have ridden.
Mineral oil does not absorb water the same way, which is why mineral systems carry roughly a two-year interval instead.
So the question 'how often should I bleed my brakes' has no answer until you know which fluid is in them.
One bike can have both
Swap a caliper, run a different brand front and rear, or buy a used bike with mismatched parts and you can genuinely have one DOT brake and one mineral brake on the same bicycle.
This is why Kuralta asks for fluid type per brake rather than per bike, and why it declines to guess: the two intervals are a year apart, and picking the wrong one either wastes a service or leaves a brake a year past due.
Calendar, not distance
Both intervals are calendar-based, which surprises people. Fluid degrades sitting still. A bike ridden twice last year is due at the same time as one ridden two hundred times.
Pads and rotors are measured, not scheduled
Shimano specifies scrapping brake pads at 0.5 mm of friction material and rotors at 1.5 mm of thickness. Those are measurements with a caliper, not intervals.
They also run the opposite way to every other kind of wear: the number goes down as the part wears out, so software that assumes bigger-is-worse will read a brand-new 2 mm pad as several hundred per cent overdue.