The term bearing test may refer to two separate things. The first usage of the term is often associated with Lexus and Nissan automobile engineering. The other refers to a road surface penetration test that is also known as the California bearing ratio (CBR) test.
When associated with automotive engineering, the term bearing test dates back to a 1992 advertisement campaign for the Lexus ES 300. In this televised advertisement, the Lexus ES 300 was mounted on a platform which allowed it to rotate across several different axes. The advertisement described the ball bearing test as an engineering test of the car's design.
In the Lexus bearing test, a silver ball bearing was placed on the hood seam of the car and released. It began to move down the seam of the hood and, as the car was rotated on the platform, it continued its journey along various parts of the car's design. The purpose of the test was to show the precision engineering that allowed the ball bearing to travel without impediment.
This version of the bearing test was later repeated by Nissan with the release of the 1993 Nissan Altima. The Nissan commercial paid tribute to Lexus by acknowledging the idea for the test had stemmed from the Lexus advertisement in their own ad campaign. The Nissan advertising team did include one subtle jibe towards Lexus, however, by remarking that the 1993 Nissan Altima was significantly less expensive than the Lexus models of the same year.
When associated with road surface construction, the term bearing test usually refers to the California bearing ratio test. This test is used to determine the suitability of road sub-grades and base courses by ascertaining the load bearing capacity of the soil sample. Higher CBR ratings are indicative of harder surfaces that are suitable for roadways and unimproved airstrips. Lower CBR ratings demonstrate soft surfaces that are not safe for roadway construction. The testing method was first developed by the California Department of Transportation prior to World War II.
The bearing ratio test is conducted either in the laboratory or in the field. Equipment for this procedure consists of a plunger of standard dimensions and a device to measure the pressure exerted on the plunger. The plunger is forced into a soil sample and the pressure required to penetrate the soil is recorded. This measurement is then divided by the pressure required to duplicate the test on a standard crushed stone material of 100% CBR. The resulting number is then given as a percentage of CBR.