Originally Posted by Marc sierra

The 2wd cossie uses 4 pistons of 40 mm diameter. I think the E38 uses 2 pistons of 40 mm and 2 pistons of 44 mm. The surface of the 40 mm piston is 1256 mm2, of the 44 mm piston it is 1520 mm2. So the 2wd cossie has a total surface of 2512 mm2 (only counting one row of pistons to be able to compare them with sliding calipers), and the E38 caliper has a total surface of 2776 mm2.

So the total surface is about 10% higher, which means 10% more fluid needs to be moved to get the same movement of the pistons. Since the difference is not that big the standard MC will be fine.

The pressure coming from the MC stays the same, so with the 10% bigger surface you also get a 10% bigger force. But the torque exerted to the hubs is also bigger due to the larger radius of the discs (about 17%).