2012 Street Tire Test | Absolutely Tired

Deciphering the Code

There are many letters and numbers on the tire sidewall —  Here’s what the important ones mean

The most important label is the sizing designation, which in this case reads “120/70ZR17”. The “120” indicates section width (120mm), the 70 is the aspect ratio (the tire’s profile, 70 meaning 70 percent of the section width), speed rating (Z, meaning the tire is rated for speeds higher than 149 mph), construction (R meaning radial), and the wheel diameter (17 inches). Following the size label is an additional marking (“58W”) defining the load index/speed rating for the tire. This designates the maximum speed the tire is rated for at the manufacturer’s maximum designated tire pressure with a specified load; thus, the 58 stands for a load of 520 pounds, while the W represents 158 mph. The difference between the load index/speed rating and the speed rating in the sizing designation is that the latter is rated at a reduced load.

Note that even though tires may have the same sizing designation, that doesn’t mean their actual sizes are all exactly the same. If you look at the spec chart on page 38, you’ll see that actual tire measurements can vary widely between manufacturers. This is important, because if you’re already very close on clearance between the front tire and the front fender, or the swingarm or chain with the rear tire, you might want to do some research to see if you’ll have any issues with another tire. Also important is that changing tires can often change your bike’s chassis attitude due to the difference in overall circumference (as well as tire profile), which will affect handling. Changes in ride height through minor spring preload or fork tube height/shock or linkage length often may be necessary when switching to different tires.

While tread patterns sometimes vary, often the only way you can distinguish the difference between the OEM variant and the standard off-the-shelf tire is the additional letter identification after the model designation on the tire sidewall. The OEM variant tires can sometimes be purchased from aftermarket retailers, but the best way is usually to order through your local dealer using the motorcycle OEM’s part number.