Originally Posted by Talk2meg00se
Went to reputable performance shop for this.
They informed that the racing compounds (ATE blue, Castrol SRF) eroded the M3 brake lines over time. In order to counteract this, stainless steel lines would be required. If only tracking 1-3 times a year, they recommended the OEM fluid (which is what I went with for 120 or so).
Wow, they really take advantage of the unsuspecting. Their claim is utter nonsense. What reputable "performance" shop will put OEM fluid knowing you're going to track the car. Tracking it 1 or 10 times isn't the issue. The issue is that during track use, the brakes are going to get VERY hot. Not only will the rotors and pads gets hot, the enormous pressure the fluid will see will raise its temperature as well, and near piston, the heat from the hot pads and rotor will transfer to the fluid, further raising its temperature.
A proper fluid, such as ATE type 200 or Super Blue have a high boiling point (dry or wet, wet meaning when the fluid has absorbed water, as brake fluid is hygroscopic). This allows them to function properly even under heavy track use, to a limit, of course. This is independent of whether you do one trac day or ten.
The number of track days will affect the brake fluid in the following way. As the fluid gets super hot during track use, you might risk boiling the fluid, and thus create air in the system. Also, even without doing that, just with the simple passing of time, the fluid will slowly absorb water and when under heavy load, that water will boil and cause air in the brake lines.
If you're familiar with how a hydraulic brake system works, you can understand the impact of air in the line.
The advantage of stainless steel lines are that they are more rigid, and when the fluid is under pressure the stainless lines have better resistance to expansion (i.e. its diameter expanding), as compared to the OEM rubber lines that will more easily stretch and expand. However, the section of brake lines that is rubber is relatively short, so the impact isn't as great as you might imagine, but it will give you better pedal feel, and ever so slightly more brake force earlier in the pedal travel.