I am trying to spec out a small dc motor for a shoebox sized car. If I have a motor with a gear on it rotating a second gear with a gear ratio of 1:1 that is attached to the axle with a wheel at each end, how can I calculate how much torque the motor needs to be capable of supplying to move the car? Car weight: 10lbs Wheel diameter: 1.75" Axle diameter: 0.125" Car speed: 1ft/s Wheel RPM (from 1ft/s and diameter): 131RPM Experimentally I found that the car requires 0.8lbs of horizontal force to start rolling from rest. I understand the effect of gear ratios (so I made them 1:1 for this question), but I am unsure how how the wheel diameter:axle diameter plays into the equation (if at all). I am also unsure of how directly to apply the force required to move the car from stop. Can this be applied to the tangent of the wheel to give a wheel torque of 0.8lb*wheel radius? Does this need to be multiplied/divided by 2 to take into account the 1 motor supplying torque for 2 wheels? Thank you for your help! Please let me know if there is any other missing piece of information needed.