What Brand Is The Longest Lived Serpentine Drive Belt?

Gates, Dayco and Continental probably make the top belts for non specialized applications. Just be careful as they all make a range so there are low and high quality belts in their lineups. I switched to Continental's Elite due to the staggered cog configuration and alignment stable backing. I do change the belt more frequently than required, but even with it's premium $30 price, it is still pretty cheap maintenance.