for your reference !
What is the difference between M2 and M3 compound?
a. M3 is the much softer compound of the two and is used when more traction is desired. The M2 will give you better tread life but less traction.
b. This is similar to the 1:8 XTR and M2 tires. The M2 is the softer of the two and will give you better traction. The XTR is more firm and will give you longer tread life. The M3 is the softest and would be used when maximum traction is needed.