FWIW, this is the way I understand the whole "driver-driven" ratio thing and how I set up my ride. This was particularly focused on the "charging" system. I wanted complete charging at idle, no issues with low RPM cruise due to 5-6 spd OD's on the highway, but wanted to keep things from getting out of control on high RPM autocross and road course outings. As an example, my 1 wire Alt. needed a minimum of 2,400 shaft RPM to work and to be activated, max rpm must be limited to 18,000 rpm. The math of: driver / driven x rpm showed me I needed- a 5.5 driver pulley with the 2.35 Alt. pulley to get to a 2.34 o/d ratio, and that would be 1,030 RPM. At the same time, my max engine rpm's to keep the alt. shaft under 18,000 is 7,692 right at my max RPM's. I see many street machines and "hot rods" with pulley ratio's all over the map, Alt/water pump/power steering and a good % of them have some sort of "charging" or "cooling" issues they struggle with. When I ask what ratio's there using, things go quite. Worst is the one's who go and buy the pulley reduction kits/set ups because they "make more power".... I tested this on the track/dyno, most times, it's a bunch of baloney as they do not tell you what negative effects it has.