SHIMANO XTR M9120 Enduro Disc Brake with Metal Pad with fins and Hose

I didn’t install them, let my mechanic handle it. These are the best breaks I have ever had.

I had been riding my Trek Super Commuter 8s+ E-bike for a year on city roads. Right away I noticed a lack of stopping power from the stock breaks. After a year I upgraded. I first bought the m9120 caliper for the front. Stopping from high speed with resin pads was noticable a lot better. After a few months I decided to also install the m9120 in the rear. I'm my case, I believed I only needed the 4 piston caliper on the front because most of the weight shifts forward when you stop. During hard stopping, the shifting of weight to the front causes less weight in the rear. Less weight in the rear wheel causes less static friction in the rear wheel allowing it to more easily lock up. I would recommend city riders only install the m9120 four piston caliper on the front and the m9100 two piston caliper in the back. It allows for better stopping control. If you're an experience racer you probably will be very happy with four piston calipers in the front and rear. Racers are used to hard stopping and will automatically shift more of their body weight to the rear to balance the weight shifts. In my experience m9120 four piston caliper in the front wheel only, is a good choice. A front and rear wheel M9120 would serve well in downhill racing or if you are doing very long decents.