In investigating the forces that tend to break up and destroy roads, the most destructive of these being that of impact, the United States Bureau of Public Roads devised a method of receiving the impact of a truck on a small copper cylinder and determining its amount by measuring the deformation of the cylinder.The impact values are largely dependent upon the type and construction of the truck. Unsprung weights have a great influence upon the impact value of the blow on the road surface and a reverse influence upon the body of the truck; these effects are in two different directions. The present aim of the Bureau is to investigate this impact and the effect of the unsprung weight on the road. Most of the tests have been made on solid tires, a few have been made on worn solid tires and some on pneumatic tires. The Bureau intends to elaborate all of these tests, including different types of pneumatic tire, different unsprung weights and special wheels, such as cushion or spring wheels.