Today’s belts are now made with an EPDM (Ethylene Propylene Diene Monomer) extended-life rubber compound.  These EPDM-constructed belts wear completely differently from Neoprene, and can last up to 100,000 miles. EPDM belt wear can be difficult to detect because the belts tend to wear like a tire tread, i.e., there is a material loss from a surface, in this case, the belt ribs.  A new EPDM belt will have a traditional “V” profile in the grooves between the ribs.  With a worn EPDM belt however, the groove profile instead has the appearance of a “U”, because of the material lost from the rib.  Once the rib profile is changed, there is less material (and therefore less surface area) coming into contact with the pulleys. This material loss can cause slippage that will affect the performance of the accessories and possibly result in an annoying noisy belt.