> So, doubling the speed > makes a four-fold increase in drag, but doubling the drive-wheel count > cuts it by a factor of 16! Careful with your wording. Doubling the drive wheel count custs the _torque induced hysteresis_ by a factor of 16, maybe, but not the losses. I'd guess that that type of loss is initially very small (but obviously grows quite quickly as you put down more torque per wheel). Grant