(In 2016, in another sub-forum, I wrote the following post that deals with the topic of MDM-and-which-brake-calipers-are-used. On a fairly regular basis, I seem to need to refer to it, and I always have to search to find where I posted it. So——I’m posting this info in my build thread, so that when the topic of MDM-and-which-brake-calipers-are-used comes up, I know where to find it. If you care at all about MDM, it's something worth checking out)
Many people incorrectly assume that MDM primarily uses the rear brakes. The fact is, MDM/DSC/Traction Control on the E9x M3 uses the front brakes the vast majority of the time.
The AIM Solo DL can track individual brake caliper activations. By comparing when you physically press the brake pedal and when the calipers are being activated, you can see where MDM steps in with the brakes, and what it does to control the situation. In my experience, 99% of MDM braking is done with the front brakes.
Using screen captures from the AIM software, we can look at MDM activity from 5 different tracks around California. Each picture is from my fastest Euro MDM-on lap at each track. I would say I wasn't making any "mistakes" but MDM was lightly stepping in to just make sure the situation was under control.
How to read the info in the pics: Each pic has five graphs lines.
-Graph 1 at the top: my actual brake pedal press
-Graph 2: Front left caliper activation
-Graph 3: Front right caliper activation
-Graph 4: Rear Left caliper activation
-Graph 5: Rear Right caliper activation
We can see where MDM is doing it's thing by looking in the blank spaces where I'm NOT pressing the brake pedal, but the computer is activating the calipers. In virtually every case at all 5 tracks, the rear brakes are basically never activated by the MDM system.
In this first chart at Buttonwillow, we can see that at 750 ft, the Front Right caliper activates on it's own. Between 6500-7500 ft, you can see the Front Left caliper is active for a whole 1000 ft as you go around Riverside which is a big rounder. The caliper activations are not huge....they're usually just nudges.
And then, you can compare that to the 6th chart at the bottom where I show my 1:49 lap at Buttonwillow with DSC-off. You can see it's totally quiet in between brake presses on all calipers.
The Big Willow chart is interesting. MDM is activating the Front Left caliper for very long stretches---1500 ft in Turn 2 and 2500 ft (!!) in Turn 8/9. It wants to make sure the rear of the car stays in the rear, so it's encouraging more of an understeer situation where it's sensing oversteer might be imminent. If you're in a rounder going to the right and the front left caliper activates, it's encouraging the front to understeer which helps keep the rear behind you. At the same time, MDM is probably holding back the rpms if you're pressing hard on the gas because it doesn't want to add more speed to the situation.
Again, the caliper activations are fairly mild, but I'd say that 2500 ft of that at 130 mph is still building some serious heat.
So, at a wide variety of tracks, it seems that DSC uses the front brakes in most cases.
Since we're on the topic, the other thing that is sort of interesting to see is how the braking system activates the calipers when you press the brake pedal. If you look at the activation profiles of the fronts, they are usually different. At Big Willow, the computer is definitely working hard trying to figure the best way to activate those calipers and keep the car going in a straight line on what is a poorly paved track. The first brake press and the press at 6000 ft are quite different between the two front calipers. At Laguna Seca, where the pavement is much better, you can see the brakes activate much more uniformly. Anyway, I find it interesting that we can see how the braking system is making [very quick] decisions to keep things under control regardless of whether DSC is on or off.
Buttonwillow: 1:51 MDM-on
Big Willow: 1:27 MDM-on
Chuckwalla: 1:55 MDM-on
Laguna Seca: 1:39 MDM-on
Sonoma: 1:51 MDM-on
Buttonwillow: 1:49 DSC-off
