I have had my 450x running for 7,864 miles and 6,510 hours. It finally needed the rear wheels replaced as the treads started to delaminate. Robotics Mower Services had had the parts and sent them out right away. I purchased the more aggressive wheels with the brushes. The installation took about 20 min including cleaning up the mower. The instructions were easy and complete. My mower is now ready for another 7,000 miles or more.