Brake Fluid

Performance and racing brake fluid

Brake fluid transmits the force from the pedal to the caliper pistons. It is the cheapest part of the braking system, yet one of those that most affects braking when the brakes get hot.

Its key figure is the boiling point. If the fluid boils inside the circuit, vapour bubbles form, the pedal goes spongy and sinks, and braking loses effectiveness. That is why the more demanding the use (mountain roads, track days, rally), the higher the fluid's boiling point should be.

Dry and wet boiling point

DOT 3, DOT 4 and DOT 5.1 fluids are hygroscopic: they absorb moisture from the air over time, and that moisture lowers their boiling point. That is why every fluid gives two figures: the dry boiling point (new fluid) and the wet boiling point (after absorbing water). The wet figure tells you how the fluid will behave once it has been in the car for a while.

Brake fluid types: DOT 3, DOT 4, DOT 5 and DOT 5.1

Type	Min. dry b.p.	Min. wet b.p.	Base	Absorbs moisture
DOT 3	205 °C	140 °C	Glycol	Yes
DOT 4	230 °C	155 °C	Glycol	Yes
DOT 5	260 °C	180 °C	Silicone	No
DOT 5.1	260 °C	180 °C	Glycol	Yes

Minimum values required by each standard. Racing fluids far exceed these minimums.

Careful with DOT 5: it is silicone-based and must not be mixed with DOT 3, DOT 4 or DOT 5.1. It is also not compatible with ABS systems. Do not confuse DOT 5 with DOT 5.1: 5.1 is glycol-based, like DOT 4.

Racing fluids available

In this category you will find high-performance brake fluids from Motul, AP Racing, Castrol and Goodridge, designed for performance driving, track days, rally and racing.

Fluid	Standard	Dry b.p.	Wet b.p.
Motul RBF 600	DOT 4	312 °C	216 °C
Motul RBF 660	DOT 4	328 °C	204 °C
Motul RBF 700	Glycol based	336 °C	See product page

Manufacturer data. Check each product page for the figures of the other fluids.

Note one detail: the RBF 660 has a higher dry boiling point than the RBF 600, but a lower wet one. A fluid with a very high dry figure is ideal if you change it often, as in racing. If it will stay in the car longer, a good wet boiling point matters more.

Tips for use

	Replace it completely: although DOT 3, DOT 4 and DOT 5.1 can be mixed, to get the performance of the new fluid the right approach is to replace it and bleed the whole circuit.
	Respect the intervals: follow the interval set by the car and fluid manufacturers. For track or racing use, check and change it more often.
	Check its moisture: with the brake fluid tester pen you will know in seconds whether your fluid has absorbed moisture and needs changing, ideal before every track day or event.
	Keep it tightly closed: because it absorbs moisture, an open bottle starts to lose performance.
	Complete the system: combine it with braided brake lines and performance pads, or see all our performance brakes.