Originally Posted by RB-MINI

A 2% ATI is 2% bigger than a stock MINI pulley. What I posted is the “stock” size ATI is supposed to be .8% larger than a stock MINI pulley so that should be factored into a pulley size decision depending on the max gas octane available in your area, or if you’re already close to pinging.

The smaller the pulley, the greater the stress and wear on the belt so I think a 15% or 17% with a 2% ATI should put less strain on a belt than a 17% or 19% alone. Others say it doesn’t really matter if you change the belt often.

I’ve read about the concerns regarding alternator and A/C speeds, but unless I’m missing something, I don’t see how the small differences in RPM’s from the chart above could really cause an issue. If you’re really concerned there are pulleys available to adjust for a larger crank pulley, at least for the alternator.