Trial by Tire

By Pat King

The Trouble With Tires
Since the test was performed in a retail store, it was fortunate that tires from three suppliers were available in a row. Samples from Michelin, B.F. Goodrich and Goodyear were used in this test.

Two key points need to be appreciated before we discuss the test. The first is that the quantity of carbon black contained in tires can vary on the order of 6 to 10 percent. While carbon is key to the mechanical strength of the tire rubber, it has a strong negative effect on the performance of RFID. Specifically, UHF RFID is known to be negatively influenced by materials with a high dielectric value. Since carbon has a high dielectric value (ability to conduct electricity), it subsequently detunes UHF RFID greatly. Thus, an RFID label's read distance performance can change depending on the type of tire to which it is applied. For example, on the sidewall of a passenger tire (containing a low amount of carbon), the read distance might be 36 inches; on a heavy truck tire (with a higher amount of carbon), it might be 18 inches; and a giant earthmover tire (which has a very high amount of carbon) might read up to 6 inches.

Tires with tread RFID labels placed in rows were tested.

If you consider placement of an RFID label on the tread of a passenger tire, you have to appreciate that the tread design pattern is a combination of rubber and air sections. Air does very little to detune UHF RFID, since it is the normalized base reference by which dielectric systems are compared. Carbon in tires, in fact, can have a dielectric effect more than 1,000 times higher than that of air. It follows that depending on the tread pattern (the ratio of air to carbon and rubber), one might expect entirely different read distances from a tag placed on the tread area. This even applies to the potential for differences depending on where the label is placed on identical tire treads. It can be demonstrated that just moving a label from one position to the next on the tread of a single tire can result in read distance differences of up to 40 percent. The same difference—or greater—exists between dissimilar tires.

Tire RFID Label Test
During the first attempt to use a handheld interrogator to read a row of tires from a distance of 18 inches, two tire labels were identified. By moving the device closer to the tires, either two or three tags were read. In a different row, only one tag was read from the same distance, though the RFID label read was not the one placed directly in front of the reader. When interrogator reader was moved closer, two or three tags were read.

During these tests, the correct tire and label in the row were never individually read, and it should come as no surprise to learn that stacks and rows behave similarly. Imagine being a technician, manager or customer trying to buy specific tires. Ultimately, picking tires based on tread-mounted RFID labels is unreliable.