What Do the Numbers on My Motorcycle Tire Mean?
Go outside and look at your motorcycle tires. You’ll find on the side multiple sets of numbers and letters. You’ll be forgiven for not knowing what all these mean, but they all communicate some vital piece of information.
The information printed on your tire's side usually includes the tire's brand and model. Additionally, you’ll find your speed and load rating, manufacturing date code, and, most importantly, the tire size.
When you need to replace your motorcycle’s tires, it is important to know this information to ensure you are putting the right tires on your bike. Putting the incorrect tires on your motorcycle can make your bike unsafe to ride.
Reading the Load and Speed Rating
When looking at the side of my Z900’s rear tire, I see that it has 180/55zr17 73W printed on the side. The first set of numbers is the tire size. The second set, 73W, is the speed and load rating.
Knowing your tire’s speed and load rating is important because it tells you your tire's maximum capabilities. The speed rating is significant if your bike sees the high speeds of the track. The load rating tells you how much weight your tires can safely support. You want to ensure the speed and load ratings are appropriate for whatever type of riding you are doing.
In my case, the 73 means the rear tire can support 805lbs. Tires are rated 43 through 90, with 43 equating to 342lbs and 90 going up to 1323lbs.
The W indicates a maximum speed of up to 168MPH. All manufacturers adhere to the same rating convention, so if you’re curious about what your tires are capable of, you can look it up below.
Reading Your Motorcycle Tire Size
When replacing a tire, you must swap it out with one the same size the manufacturer recommends. You can quickly tell what size tire you should have on your bike by consulting the owner’s manual.
You will also find the size printed on the sidewall of your motorcycle’s tire. My rear tire has 180/55zr17 printed on the side. The first number, 180, corresponds to the tire's width in millimeters meaning that my rear tire is 180mm wide.
The second number, 55, is the aspect ratio for the tire’s height expressed as a percentage of the width. To find the height of your tire, you multiply the width of the tire, in this case, 180mm, by the aspect ratio. 180mm x 0.55 equals 99mm. I now know that my tire is 180mm wide and 99mm tall. I promise that’s the hardest math we’ll have in this article.
The third number, 17, is the wheel size in inches, and there you have it. You now know how to read the size of your motorcycle’s tire.
Why Is It Important To Know the Correct Tire Size?
Making sure the tire you are buying fits is the most obvious reason you want to confirm that you’re choosing the correct size, but more than that, you want to ensure that the tire is safe. An improper fitting tire could reduce the contact patch with the road or the bike's riding characteristics, resulting in a dangerous situation.
Buying a tire with the appropriate speed and load rating also ensures that your tires can safely accommodate the type of riding you do. If you’re taking your bike to the track, you need tires capable of handling those speeds. Likewise, if you have a heavy cruiser bike that you load up with luggage, the tires need to be able to bear that load.
What Other Information Is on Your Motorcycle Tire
In addition to your motorcycle tire’s size, speed, and load rating, you’ll find plenty of other information printed on the side of your tire worth knowing.
The most obvious information will be the tire's brand and model. I have Shinko R009RR tires on both my front and rear wheels. If I wanted to replace them with the same tire, I would search for a replacement tire on Revzilla or Cycle Gear. With the tire's size, brand, and model, I have all the information I need to replace it with the same tire.
Some other good information to know is going to be the manufacturing date code. As tires age, the rubber starts to degrade and lose its performance. The date code helps you know exactly how old your tire is.
Expressed as a four-digit code, the production date of your tire is easily decoded. The first two digits are the production week, and the second two are the year. For example, 1821 would be a tire made on the 18th week of 2021.
You can also find the directional arrow to know that your tire is mounted correctly. The arrow should be pointing towards the front of the bike. Ensuring that the tire is mounted correctly is critical so that the tread and rain grooves work as they should.
When Should You Replace Your Motorcycle Tires?
Motorcycle tires wear down over use quicker than car tires because the rubber is made of a softer and stickier compound than car tires. It can be a little surprising just how fast motorcycle tires require replacing.
Using a tread depth gauge, you can check how much tread you have left on your tires. Motorcycle tires also have a wear indicator in the tread. Once the tread wears down to the indicator strip, it is already past time to replace your tires.
If your bike has been sitting especially long, it is also a good idea to replace them at least every five years. Over time the rubber on tires hardens, and it loses traction.