MS3 - Soft / Intermediate Terrain. MH3 - Intermediate / Hard Terrain. For the M12 and S12 tires, the sizes are as follows: 100/100-18 = Michelin size of 120/90/18. 100/90-19 = Michelin size of 120/80-19. 80/100-21 = Michelin size of 90/90-21. Note: Please check your current tire size to ensure you are ordering the correct replacement size.