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I participated in X3M / X4M discussion about 6-piston calipers. Sharing this information. Hopefully it will be of help.

There is a lot of confusion about brakes and 4-piston and 6-piston calipers.

While tires help the vehicle stop, brakes create clamping force. Clamping force is a result of several elements working together - while meeting a myriad of requirements such as weight, size, cost, brake pad size / shape, ease of brake pad changes, and stiffness.

- Line pressure: generated by the master cylinder
- Rotor size: influences leverage / effective radius
- Number of pistons and size of pistons: or piston volume which directly translates into the clamping force

The number of pistons has no absolute bearing on the clamping force. 4, 6, or even 8 piston calipers with the same piston volume will offer the same clamping force (a simplified view).

The actual differences in clamping force depend on the size of pistons, spacing of pistons, how the caliper was designed (AP Racing calipers are a work of art), and size / shape of the brake pad.

So how can a 6-piston caliper be more effective? It can - if properly designed.

The brake pad can be larger (visually taller following the outer edge of the rotor) increasing the contact area. The brake pad surface area is a function of how brake force is calculated. In addition, as 6-pistons work together to distribute pressure on the brake pad, the brake pad taper is reduced. Brake pad taper reduces contact area, decreasing clamping force. Longer and wider brakes pads dissipate the heat better.

In a 6-piston caliper, pistons can be smaller and placed farther from the rotor center increasing leverage.

In short - it's worthwhile to understand how brakes are designed.

AlexFL experience with Brembo GT brakes on X3M at https://x3.xbimmers.com/forums/showthread.php?t=1723703.