He asked what the difference between M2 and XTR was...
This is the difference: "Pro-Line 1/8th scale buggy tires are generally available in M2 and XTR compounds. The XTR compound is the hardest compound and will provide the longest tire life and works best on hard packed, dry tracks with high traction. If the track is wetter or less hard packed, the M2 compound tires will provide better grip with decent wear, but will generally wear faster than XTR compound tires."
Source:
http://www.amainhobbies.com/product_info.php?products_id=3181