Safe: that's true. sometimes you see a hub-motor that is only 3 inches in diameter and is SUPER discreet... but I don't believe they can create much torque.. and sometimes you see a hub-motor that is 8 inches in diameter. They can both be rated for the same power but I think the larger ones create more torque, if you visualize how the power created by the "larger" motor is further away from the axle and the concept of mechanical advantage.