This is a more complicated issue than it might appear, because "towing capacity" is more of a sales specification than a technical specification.

If you picture yourself pushing a wheelbarrow full of dirt, weighing about 300 pounds, you would say that your "pushing capacity" was at least 300 lbs, but I doubt you would be able to push 300 pounds if it were on a flat sled with no wheels on rough ground. That is a simple analogy explaining why we don't use towing capacity as a technical specification.

Everyone likes to relate axle torque to draw bar force, but draw bar force cannot so easily be related to "towing capacity" due to all the variables involved. There is also a difference between a maximum axle torque (or draw bar force) short duration spike compared with what can be sustained over a long distance such as in towing.

On most surfaces, unless you significantly weight down the tractor, you will generate tire slippage before you reach the transmission's ability to create maximum axle torque.

CAUTION: You should also be concious and cautious of the vehicles "braking ability" whenever using it for towing. Most of these tractors have a single disc brake designed to stop the weight of the tractor on slight grades. When you are towing downhill your braking distance will significantly increase.

As a general rule of thumb, using a single-axle wheeled trailer and using a properly maintained and adjusted tractor, you should be able to pull approximately half the weight of the tractor fairly safely and with control over level ground and over slopes less than 5 degrees.