The graph indicates that this motor has a maximum efficiency of less than 50 percent. The curve for the low friction case shows a much higher efficiency, indicating that the motor's friction is a significant problem. The horizontal axis of this graph is current. Another thing to remember is that, for a particular applied voltage, speed and torque are intimately related. So the speed of the motor is maximum when torque is equal to the frictional torque.
Speed declines linearly with increasing torque increase until it reaches the stall condition.
The easiest parameter of the Solar Sprint motor to measure is it's electrical resistance. This can be measured with an ohmmeter. Because this motor has rather poor brushes, it is a bit difficult to get a consistent reading. It helps to run the motor for a while first. On the samples that we tested, a motor resistance of about one ohm was measured.