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Brake Fluid data


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Collected some data on high performance brake fluids and thought to share




What I gathered is that Endless fluid gets a much more consistent pedal feel throughout session due to lower compressibility and used by many teams 

SRF best for minimise bleed inbetween events due to highest wet boiling point, also used by many teams

Motul gets mixed reports but could not find more data





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Adding to this post


Some testing here that talks about hygroscopicity and why it matters



Below is  a write-up I have found and modified slightly as Q&A format on why good hygroscopicity is important





What is a hygroscopic fluid?

Glycol based fluids are hygroscopic which means they absorb water/moisture from the environment at normal atmospheric pressures at a rate of 2-3% per year. This process is exasperated in more humid conditions and climates.

The hygroscopic nature of DOT brake fluid is actually an advantage in a major way.


So where does this water come from? What are the effects of water absorption?

This water content finds it's way into the brake fluid via microscopic pores in brake hoses, seals, joints and seams. Water mixed with DOT fluid has an adverse effect on the brake fluid by reducing it's boiling temperature and therefore reducing it's performance.

As water enters the system, instead of pooling in low spots (such as the caliper), due to it's weight in comparison with brake fluid, it is dispersed throughout the whole of the brake fluid. This helps to keep the boiling point of the entire brake fluid high rather than having pools of water in the system which will boil much sooner than the rest of the brake fluid. It also prevents localised corrosion of internal parts which can be caused by water pooling in the brake system.


What about mineral oils?

Unlike DOT fluid, Mineral Oil is hydrophobic and does not absorb moisture from the environment. This means that there are no wet or dry boiling temperatures to worry about, the boiling point stays constant and never drops. That's the good news.

The bad news is that any water that does enter the brake system, via seals or microscopic pores in the lines etc., will effectively reduce the boiling point of the whole brake system to that of water - just 100°C. This is because as the fluid repels any water ingress, it causes it to pool at low points within the brake system, usually the caliper, since water is heavier than brake fluid it will settle at the lowest point. This is worrying because the fluid in the caliper is more susceptible to high temperatures as it's at the business end of the brake, where the friction is created.



A good level of hygroscopicity fluid does not necessarily mean more brake fluid swap and corrosion, but actually help protect the brake system from the risks of water pooling and low wet boil temperatures.




Edited by Peopleandcars
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