Belts
Been using the so-called "new" knurled Kirby belts for years and have never broken one. I'll wager Vinvac is right. If the machine is set too far down, the belt probably wears quicker. Besides, air flow is restricted. We had a thread about this in April, I think, and one of my conclusions is that with Tech Drive, it's easy to push the machine at any setting and sales people don't emphasize finding the optimal settings anymore.
