Motocross Stopping Power: The Science Behind Brake Fluid's High Boiling Point | Moto-House MX

Motocross Stopping Power: The Science Behind Brake Fluid's High Boiling Point

Motocross Stopping Power: The Science Behind Brake Fluid's High Boiling Point

Brake fluid for motorcycles and dirt bikes is designed to withstand the high temperatures generated during braking, thanks to its high boiling pointHowever, it gradually absorbs moisture from the air over time due to its hygroscopic nature.

Fresh, clean brake fluid can boil up to 230°C (446°F), depending on the fluid (see the chart below). In contrast, water boils at just 100°C (212°F). The more water the brake fluid absorbs, the lower its boiling point gets. Hard braking generates significant heat, further elevaing the temperature of the brake fluid. (See Chart Below).

If your dirt bike's brake fluid has too much water, it may boil and make steam. Unlike brake fluid, steam can compress. Consequently, when hitting the brakes, the steam may compress instead of applying sufficient pressure on the brake pads. This can make your brakes work worse or even fail, as the steam prevents the appropriate amount of force from reaching the brakes.

Dry Boiling Point                 Wet Boiling Point
DOT 3 205°C/401°F            140°C/284°F
DOT 4 230°C/446°F            155°C/311°F
DOT 5.1 260°C/500°F          180°C/356°F

Modern motocross bikes across the 50cc, 65cc, 85cc classes, and full-size models have small rear brake reservoirs. This can lead to the fluid heating up rapidly due to the limited volume.

Additionally, motocross riders frequently apply more force to the rear brake for air control and tight maneuvers. This heavy usage further speeds up the temperature rise, increasing the likelihood of brake fluid boiling.

To prevent these issues, riders and mechanics often use higher-grade brake fluids with higher boiling points. Regular maintenance and checks are crucial to ensure that the brake fluid is in good condition and hasn't absorbed too much water, which would further reduce its boiling point and braking efficiency.

Flushing your brake system is straightforward and doesn't require special tools—just brake fluid.

Don't wait until the brake fluid darkens in color or the brakes feel spongy; by then, it's already too late.

For preventative maintenance:

  • Street Bikes: Flush brake system every 10,000 miles or 2 years.
  • Dirt Bikes, ATVs, UTVs: Flush system every 40 hours of use.

A simple upgrade you can make to your bikes is to switch to DOT 5.1 brake fluid.

Switching to DOT 5.1 brake fluid from DOT 4 is straightforward since they blend easily, both being glycol-based. However, it's crucial not to confuse DOT 5.1 with DOT 5; DOT 5 is silicone-based and incompatible with other fluids, posing a risk of brake failure.

The high boiling points of DOT 5.1 fluid (DOT 5.1 260°C/500°F) ensure improved braking performance, even under extreme heat or during racing conditions. Therefore, when making the transition to DOT 5.1, ensure it is the correct type for enhanced brake safety and functionality.

Maxima Racing Oils DOT 4, Racing DOT 4, and DOT 5.1

MOTOREX Brake Fluid DOT 4, DOT 5.1

MOTUL DOT 5.1 Brake Fluid 

Here are Some Helpful Tools for Maintaining Brake System:

A really useful tool to check for water in DOT 3 and DOT 4 brake fluids is the Bikeservice Brake Fluid Tester. It helps you monitor the condition of your brake fluid better.   

BikeService - Brake Fluid Tester - BS5630

This tool: Phoenix V-5 Bleeder Brake & Clutch simplifies and speeds up bleeding brakes and clutches. Its standout Reverse Bleed Technology excels at air removal. It's perfect for refilling and air-purging completely dry systems, in-vehicle or bench setups. Works with DOT 3, 4, and 5.1 fluids and is incredibly user-friendly.   

Phoenix V-5 Reverse Bleeder Brake/Clutch - 2104-B -Reverse Bleed Technology
The Motion Pro Mini Bleeder is a dual-purpose tool designed to streamline the process of bleeding brakes and hydraulic clutch systems. It ingeniously integrates a wrench and bleeder valve into a single, handy device. Crafted from anodized billet aluminum for the handle and chromoly steel for the body, it is engineered for both duraility and aesthetics.  
Motion Pro -Mini Bleeder - Brake & Hydraulic Clutch System Tool
In conclusion, the high boiling point of brake fluid is critical for the demanding conditions of motocross riding. Regular maintenance and selecting the right type of brake fluid is key to ensuring that your brakes respond when you need them most. Stay ahead of the curve by keeping informed on the latest products and best practices for your motorcycle's brake system.

Looking for More Brake Parts Rotor, Brake Pads, Brake Lines, Brake Levers, Brake Pedals

The Team at Moto-House MX would like to thank you for reading our latest blog post. As a token of our appreciation, we're excited to offer you a discount code for use on any purchase. Simply enter 'Moto-Disc' at checkout to enjoy your savings!


Back to blog

Leave a comment

Please note, comments need to be approved before they are published.