Wheel torque determines how fast a car can reach a particular speed. The higher the torque, the faster the acceleration. The units of torque are pounds per feet.
One way to explain the way torque works is to imagine trying to loosen a stubborn nut with a socket wrench. Trying to turn the wrench up the neck, near the bolt, produces little in the way of results because the torque is limited. Turning the wrench down at the other end of the handle is easier because the torque is greater. To calculate torque, divide the weight applied toward the motion by the number of feet away from the hub that the weight is applied.
The difference between torque and horsepower is that one multiplies torque by speed to get horsepower. One horsepower is the same as 33,000 ft/lbs of force per minute. Three different factors go into this calculation: the amount of weight being moved, the distance of movement desired and the length of time necessary. If the car has little wheel torque, it's necessary to downshift more often to get rev range higher and show the engine's power. These engines are cheaper but have to work harder to achieve the same speed as engines with higher wheel torque.