[smchuck]

Thinking about getting the car ready for summer track season. Will swap in the summer wheels/tires and the Hawk HP plus sport pads. I used these pads last summer then swapped then out for Hawk HP street pads for the winter. Not much wear on them from last summer.

Last summer I had a mechanic do a complete brake fluid flush and put in Motul 660 so the fluid is 1 year old. 6 track days last summer. At least 7 planned this year.

This summer I'm thinking I might just empty the reservoir, refill, bleed myself and not worry about the ABS and doing a 100% flush. Then next year go back to mechanic for complete flush and fill.

Any thoughts? Thanks,

Chuck

[dradernh]

Originally Posted by smchuck

Thinking about getting the car ready for summer track season. Will swap in the summer wheels/tires and the Hawk HP plus sport pads. I used these pads last summer then swapped then out for Hawk HP street pads for the winter. Not much wear on them from last summer.

Last summer I had a mechanic do a complete brake fluid flush and put in Motul 660 so the fluid is 1 year old. 6 track days last summer. At least 7 planned this year.

This summer I'm thinking I might just empty the reservoir, refill, bleed myself and not worry about the ABS and doing a 100% flush. Then next year go back to mechanic for complete flush and fill.

Any thoughts? Thanks,

Chuck

TLDR; full flush, including ABS, with a very low viscosity racing brake fluid; if you run the car hard with race pads and sticky rubber, at a minimum bleed between events; my 2¢, of course

All the stuff below is about ABS and fluid viscosity.

This blog post on Essex Parts' site is a useful read for general racing fluid background information: https://www.essexparts.com/news-blog...ng-brake-fluid.

This brake fluid comparison chart has some information regarding fluid viscosity, including stating that late model BMWs are using "ultra low viscosity" brake fluid: https://www.lelandwest.com/brake-flu...ison-chart.cfm.

I mention ABS because in 9 days of track driving I experienced ABS engagement exactly one time, and that was during my first session during my first track day in the M240i. The car had a brake fluid flush with Castrol SRF before each event. The ABS system didn't have its fluid replaced during any of those flushes.

I've stopped going to the track but before my next event was going to have a complete fluid change to AP Racing Radi-Cal R4, ABS included. The purpose was to see if I began engaging the ABS in the only braking zone where it should have been operating: slightly downhill, moderate grip, 138-to-85 MPH at turn-in, with a further decel to 58 MPH at the apex.

In cases like this, it's always possible the driver simply isn't pressing hard enough on the brake pedal to engage the ABS. Driving coaches have been known to shout to their clients "Push the pedal through the floor!!!"

I know the process for finding a car's shortest stopping distance but didn't go through the exercise with my M240i. With DTC-70s and 255 R888Rs, though, I believe the car should have been well into the ABS in that braking zone.

I just called up the data from one of my faster laps, and it's clear I wasn't on the brakes strongly enough to get the most out of the car and likely not enough to engage the ABS. During the hardest of the straight-line braking, the car was at -0.85g to -0.87g for 299'. Further data shows that factor could have been in the neighborhood of -1.15+g.

Frankly, I wasn't inclined to run a heavy car like ours any harder into both that braking zone and the subsequent turn, in effect giving up the benefit of ABS assistance for feeling more comfortable. YMMV.

On top of that, my brakes got extremely hot at Mid-Ohio with its single heavy-braking zone. I've noted my car's rotor and caliper temperatures in the Tracking subforum. My results tell me owners may not want to trying getting the absolute most out of their brakes unless they're prepared to examine their calipers' dust boots and piston fluid seals on some sort of regular basis. Bimmerworld sells complete dust boot/fluid seal replacement kits.