Overloading a truck can be dangerous. With a load beyond its capacity to handle, a truck will brake and steer incorrectly. If the load is badly distributed it may also tip over the vehicle. Beyond immediate dangers to safety, overloaded trucks also damage roadways by exposing them to loads beyond their design tolerances. A truck's driver is responsible for not overloading it and can be fined heavily if caught overweight. Fortunately, it is easy to tell if a truck is overloaded.
Check what load the truck is rated to carry safely. This should be printed on a plate somewhere on the truck body. Otherwise, consult the truck's manual or contact the manufacturer.
Drive the truck to a weigh station before loading it and note its empty weight. These stations are at intervals on most major highways or you could visit anywhere trucks are charged by the weight of material they bring in or out. These locations include garbage dumps and gravel quarries.
Drive back to a weigh station once the truck is fully loaded with the goods, people and tools it will carry on the road. Note the weight of the truck loaded in such a way and subtract the weight of the empty truck. If this number is higher than that which the truck is rated to carry, some cargo will need to be offloaded.
Look carefully at the suspension springs on each wheel. If they are fully compressed, the truck is overloaded. This can also be checked on smaller trucks by jumping up on the truck's bumper. If the truck bounces, there is still some give in the suspension system. If it does not, it may be overloaded.
Bring the truck up to speed in a parking lot or other empty space and brake normally. If braking takes significantly longer than under normal conditions, it's a sign of overload. Any added weight will lengthen stopping times, but an overload will make these times long enough to be dangerous on the road.
Look at the truck from the back and check for any tilt in the bed. A badly centered load can overload one side of the truck, even if the overall weight is within tolerances. This may lead to the truck flipping over on the road.
