The sides of a motorcycle tire can be a bit confusing if you are not familiar with the numbers and codes printed there. There are both old English and metric measurements used here, so that can add to the question marks in your head. So, to help with this, below is a very basic explanation of how you read a tire so that you know it is the right one for your ride – or, so you know what other riders are using.
The first number, 180 in this case, is the measurement of the tire’s width in millimeters when fully inflated. 180 millimeters is 18 centimeters or about 70.9 inches.
Our second number, 55 here, is the aspect ratio of the tire. This means that the tire’s measurement from inside the bead (which sits inside the wheel rim holding the tire within it) to the top of the tire is 55% of the tire’s width. In this example, 55% of 180 millimeters is 99 millimeters or 3.9 inches.
The first letter is the speed rating. In our example the letter is Z, which means that the tire is designed to handle consistent speeds over 149 miles per hour – meaning here that this tire should handle any speed this motorcycle can reach, within reasonable limits.
The second letter here is an indicator of the tire’s construction. In this case the R indicates that it is a radial (tubeless) tire and is only suitable for wheels designed for such. Another letter you may see here is B, for belted, and motocross tires usually do not have any indicator.
The final two numbers indicate the size of the wheel, in inches, this tire will fit. For our example, that number is 17, which means it is for a 17 inch wheel.
You may also find a load rating elsewhere on the tire. For the tire example above, the number is 73W, which means that the tire is designed to withstand no more than 805 pounds in total. There are numerous codes here, so please see the chart below for more information.
The information above applies to most motorcycle tires, but there are other markings located on tires (ortyres) which differ from region to region; each country or group of nations has its own regulating body. Most tires sold in United States and Europe will have a Department of Transportation date code.
Reading this is rather simple; for example “DOT U2LL LMLR1908” means that the tire was manufactured during the 19th week, based the “19” from the last set of four numbers, of 2008, based on the final “08” numbers of that sequence.
The final set of four numbers is all that you really need to know as the other letters and numbers – beyond the “DOT” which indicates Department of Transport(nation) – designates the location the tire was produced, the tire’s manufacturer, and the tire’s size.
Before the year 2000, though, the tire date code was only three numbers in length. The first two numbers indicated the week of manufacture, as they do now, but the final number was the year of the decade in which the tire was produced. For example, “…199” would be translated as the 19th week of the 9th year of the decade. Yes, that would cause significant confusion for tires more than 20 years old now, but then those would be risky tires for a motorcycle anyway.
In Europe, there is a further designation indicating which European Tyre and Rim Technical Organisation (ETRTO) regulation the tire was manufactured under; this is determined based on the tire’s specified use. An example would be “E2” – the “E” indicates that the tire conforms to ETRTO standard R75 and the “2” means that the tire was approved for this regulation by the nation of France.
Other areas of the world may vary, so please seek out the proper information from your nation’s DOT.