[blykins]

When the crank pulley is larger than the accessory pulleys, then it's an overdriven pulley system. Likewise, when the accessory pulleys are larger, they're underdriven.

So of course in an underdriven situation, the accessories are now turning slower than in a stock situation. You have to watch because if you turn accessories slower (i.e. alternator), you might end up with some side effects.