speyfitter

If you have the exact same rotor, say the SM-RT 66, same diameter, etc. and use appropriate metallic pads - what is the difference in brake performance going to be between base 2 piston Shimano MT200s and their highest end 4 piston brakes (say whatever XTR model) going to be? There will obviously be a difference in stopping power but what about when brake fade kicks in?

BlazingPedals

I've never had hydraulics, but I always thought the 4-piston designs just controlled the pads better for less squeal, not necessarily more braking power. I'll sit back to hear from those who know better than me.

Troul 

it'll likely be more touchy with more pistons in that comparison. The fade in theory would happen a littler quicker as the operator might squeeze the lever hard initially giving the system a large frictional heat event & as the operator tries to modulate it, the frictional heat continues to build up.
I wouldn't spend the cash on swapping out a 2 piston for a 4 piston with everything else staying the same.

msu2001la

Less fade is the main benefit here.

Either system is more than capable of exceeding the available traction from your tires with a simple squeeze of the lever, so while a 4 piston setup will provide more "stopping power" it isn't likely to actually stop your bike any faster. There are some differences in feel and modulation, which is largely subjective. Unless you're a downhill racer or riding a heavy e-bike, or tandem/etc and finding that your 2 piston setup is frequently fading out on you, switching to a 4 piston setup isn't going to really change anything. They work as advertised, but are overkill for most people.

msu2001la

4 piston designs can run larger pads, so there's more surface area to grab the rotor (stopping power) and more surface area to dissipate heat (which will reduce fade).
With two pistons pushing in each direction, there's more power at the caliper so I think this translates into less force needed at the lever.