4th gear on my car is nearly 1 to 1, but I still need the gearbox for the differential reduction (and for something to bolt the motor to
). Overall reduction in 4th is around 5 to 1. I can't comment on compound wound motors, but for a series wound motor I would expect the same results. It should climb the hill with 24 volts. It should even do it at 12 volts, but at half the speed. Amps = torque and volts = rpm. Increasing voltage just increases rpm. If you want more torque you have to increase amps.