What is the difference between the John Deere 6M 230 and 6R 230?

Here is how the John Deere 6M 230 and John Deere 6R 230 compare on John Deere's published specifications:

• Horsepower: John Deere 6M 230 227 hp vs John Deere 6R 230 227 hp
• Pto horsepower: John Deere 6M 230 184 hp vs John Deere 6R 230 184 hp
• Weight: John Deere 6M 230 21164 lb. vs John Deere 6R 230 21716 lb.
• Fuel capacity: John Deere 6M 230 108.3 gal. vs John Deere 6R 230 107 gal.
• Wheelbase: John Deere 6M 230 114.2 in. vs John Deere 6R 230 114 in.