What is the difference between the John Deere 9R 640 SCRAPER and 9RX 640?

Here is how the John Deere 9R 640 SCRAPER and John Deere 9RX 640 compare on John Deere's published specifications:

• Horsepower: John Deere 9R 640 SCRAPER 631 hp vs John Deere 9RX 640 631 hp
• Weight: John Deere 9R 640 SCRAPER 45122 lb. vs John Deere 9RX 640 56981 lb.
• Fuel capacity: John Deere 9R 640 SCRAPER 400 gal. vs John Deere 9RX 640 400 gal.
• Wheelbase: John Deere 9R 640 SCRAPER 154 in. vs John Deere 9RX 640 162.5 in.