How does the relationship between pressure and boiling point in the brake fluid work to cause overheating to catastrophically reduce performance?
My (naïve, empirically clearly flawed in some way) expectation would have been that, while gasses are compressible and liquids are not, pressures high enough to cause compressed gas to have lower volume than the liquid that boiled off to produce it would cause the gas to condense back to liquid; while temperatures high enough to overcome pressure and keep some amount of liquid boiled off and in a less dense gas state would increase pressure in the system and, if anything, cause the brakes to go into runaway braking rather than stop braking.
Am I misjudging the viability of a point on the phase diagram where the gas is more dense than the liquid that produced it; misunderstanding how pressure is distributed in a brake system; or focused on the wrong area and the actual problem is chemical degradation or the hydraulic system being fluid-tight but leaking gasses or some other issue?
The main problem would be where to dump the energy. I doubt the battery would like the charging amperage needed for heavy braking, and any big ass resistor would heat up just like physical brakes.
If only there were some kind of coil that could turn the energy into electrical discharges…
I’m still blown away that a Tesla Model S Plaid, a car that starts at $130k and is marketed specifically as being a high performance track monster, has DOT3 fluid. My freaking Subaru WRX was well over 4x cheaper, has normal steel brakes (no exotic carbon ceramic brakes like a Plaid), and still uses DOT4 fluid FFS. Seems like a really dumb cost saving measure on the part of Tesla.
First off, I’m surprised that Tesla didn’t use Dot 4 or better from the factory. Secondly, if you don’t know the proper way to do something, take it to someone who does. Clearly, he had the money to buy expensive brake components, but not enough sense to buy a cheap bottle of brake fluid! I converted my Mk1 VW GTi to 4 wheel disc and larger front rotors, AND CHANGED TO SILICONE BRAKE FLUID! And I didn’t run it at anywhere close to those speeds. Thanks to factory gear ratios, it was limited by RPM to about 130, but never experienced any braking issues. Before you make your car go fast, make sure it stops fast.
Wait, so someone obsessed with fast cars (who, let’s be honest, only owns a Tesla Plaid because the 0-60 time is super fast, he’s a total petrolhead otherwise) is way worse at driving than he thinks? And makes dumb mistakes when modifying his vehicle? You don’t say!
I do not understand this preoccupation with traversing flat sections of pavement at high speeds. I stopped playing with Matchbox cars several decades ago.
All hydraulic brakes are automatically adjusting. They have a fluid reservoir near the master cylinder that is open to the brake line when the brakes are released. This acts as a pressure relief/extra fluid reservoir to deal with things like thermal expansion and contraction of the brake fluid and lines, as well as well as wear of the pads and rotors. So if the brake fluid heats to the point of boiling, next time you release the brakes, the gas is going to push some fluid back into the reservoir to equalize the pressure, and now you have less fluid in the actual brake lines since some is replaced by vapor. Next time you press on the brakes you will be compressing the vapor rather than the calipers.
The brake system has a valve that lets excess fluid back into the reservoir on the release stroke. The boiling fluid has a lot more volume than liquid fluid has, so that valve gets opened and your fluid goes bye-bye.
