Next to the motor the treadmill belt is the most important part of the treadmill. If it becomes frayed or starts to turn up on the sides then it is time to replace the belt.
How to replace your treadmill belt
Is your treadmill belt worn, torn or curling up on the edges? Does your treadmill slow down after you step on the belt and begin your workout?
If this is the case then it may be time to replace the belt.