Torque is converted to a linear force with the gears and wheels.
The force to overcome includes the mass times acceleration, plus gear friction, not just be stationary mass.
The surge current or stall current rating is generally 5-8x the average max current determined by Rs winding resistance will decline slowly until it reaches cruising speed.
Power dissipated in a current limited motor will then dissipate V²/Rs power or I²Rs until it speeds up. since I surge will average 5x it means 25x approx the power it is rated for. if overloaded. it will remain stalled.
The unit must be rugged enough to withstand the heat and thus have more torque and requires more current than you calculated and less Rs than you expected. Then the acceleration must be controlled slowly and efficiently with PWM with a heavy mass.
Power and heat loss calculations are necessary with all variables of m, a, V+ , Rs , RdsOn ESR (bat) etc
TORQUE = FORCE x RADIUS
FORCE = MASS x ACCELERATION
HP = TORQUE x RPM x 6.28 ÷ k
http://viewmold.com/Products/Techni...ars/Gears-HOW TO FIGURE HORSEPOWER TORQUE.pdf