Calculating Tow Capacity

IS IT WORTH DOING THE MATH?

Yes! It all comes down to safety. A tow truck is like a big lever with the fulcrum (or pivot point) at the rear axle or axles. When we load weight behind the rear axle (or axles), we unload weight from the front axle. (Ever seen a tow truck that looks like its front wheels are barely touching the ground? That’s a really unloaded front axle, and a very unsafe situation.) Unloading your front axle directly affects the braking, steering and handling of your tow truck. That’s the safety part. But unloading your front axle also reduces equipment life, since it risks overloading the frame of the chassis, the lifting devices, suspension components and the tires.

DOESN’T MY OWNERS GUIDE TELL ME MY MAX CAPACITY?

Not really. If you calculate the actual towing capacity, you may get a substantially lower or even higher number than the guidelines state, since how you set your overhang will dictate the capacity. You may have your overhang extended as far as possible, but the max towing capacity in your owner’s guide will assume your overhang is at its shortest possible length.

The towing capacity rating that is provided to you by the manufacture is detailing the structural capacity of the under reach. Once you mount the under reach to a chassis you must calculate the actual towing capacity for that specific truck using front axle weight, wheel base and overhang.

This towing capacity formula will give you the front axle weight of the casualty you can safely tow under ideal driving conditions.