I've recently been toying with the idea of working on the pulleys on my Sram Rival. In a recent article about Fabian Cancerella, Shimano was making a special rear derailleur for him that had extra large guide (top) and tension (bottom) pulleys that supposedly transferred power better. His also had a large cover for aerodynamics but that is beside the point.
Fast forward to Thursday at the Bike Authority and we looked around for larger pulleys. It turns out Trek mtbs. with a "super-low" or 34t cog resulted in a red 15 tooth pulley compared to the usual 11t. We had plenty of those so I searched around for a very lightly used (not worn down) tension pulley. I cleaned it up and put a touch of lube on it ready to put on the Cannondale.
Friday morning we had more time to experiment and put one on my bike. We replaced my 11t sealed bottom pulley with the red 15t. The first test it would go through would be Reagan Park on my cross bike. We made it .6 miles before I was shifting up to an easier gear and rode of a small root. CLING! CHICK! STOP! I dismount to see what the problem is and my whole rear derailleur is jammed up in my spokes and totally done.
Most likely the cause was the oversized pulley slipping (or something else) but it could have been a freak accident. Either way, my road/cross bike is not getting any new and faster pulleys, instead a new derailleur. I'm kind of disappointed as I thought this would really work and we could cut the pulley so we could put some sealed ceramic bearings in there and maybe offer to customers. So this post should really be called DO NOT ATTEMPT instead of make me rich.