Decipher the Codes

Sometimes it seems as if there should be a codebook to understand all of the information on a tire's sidewall. Using a Bridgestone BT-010 as an example, here's what some of the markings represent.

The most important label is the sizing designation, which in this case reads "120/70ZR17." This label indicates section width (120mm), aspect ratio (70 percent), speed rating (Z), construction (R), and wheel diameter (17 inches). For our BT-010, note from the table above that the actual section width is 121mm, and the section height is 69mm. Added to the 20mm bead dimension, overall height is 89mm, giving an aspect ratio of 73 percent. This tire has a speed rating of "Z" or more than 149mph, and is a radial (R) construction. Following the size label is an additional marking defining the load rating for the tire. In this case, "58W" indicates the total load carrying capacity is 520 pounds.

The tire shown is taken from our Honda CBR600F4i and is a slight variant of the standard BT-010. While the first "F" denotes this as a front tire, the second "F" indicates the OEM variant. These model-specific tires are subtly modified from the standard units as requested by a specific manufacturer, whether for lighter weight, better mileage, or even a slightly different tread pattern. OEM tires are available through your dealer using the manufacturer's part number. Also marked on the side of each tire is the number and type of plies in the tread and sidewall construction. For our BT-010, two rayon plies run across the tire from bead to bead, while two aramid and two rayon plies make up the tread's belt package. Note that this particular BT-010 from the CBR differs in construction from the standard Bridgestones tested, and has more plies in both the tread and sidewall.

There's still more information molded into the side of a tire, but that's the basic and most important data to consider when replacing tires.

This story was originally published as part of the tire test in the June 2002 issue of Sport Rider.