Reading Your Motorcycle Tire
If you were to go outside and look at your motorcycle tire right now, would you know what the numbers printed on the side mean? All tires will have a series of numbers somewhere on the sidewall that indicates the tire size, load rating, and speed rating.
My bike has a Shinko R009RR tire that reads 180/55zr17 73W on the rear. Upfront I have the same tire but it reads 120/70r17 58W. What do these numbers mean and why are they different from the front to the rear?
Tire Size
The first number you see on a tire is the width of the tire in millimeters. You may have noticed looking at your bike that the rear tire is significantly wide than the front tire. In my case, my rear tire is 180mm while the front is 120mm.
The second number is representative of the aspect ratio of the tire's height relative to its width expressed as a percentage. For 180/55 that means my rear tire’s height is 55% of the width. That would mean my rear tire is 99mm tall.
The third number is the rim size of your wheel. In this case, my rear wheel and front wheel are both 17-inches. However, it is very common to have a larger rim on the front relative to the rear, especially on cruiser bikes.
Speed and Load Rating
The next set of numbers that you will see on your tire is the speed and load rating. This is denoted by a double-digit number followed by a letter. In the case of my tires, the number 73 would equal 805lbs and 58 equates to 520lbs. The letter W means the tires can safely be operated up to 168mph.
You might be wondering why the front and the rear have different load capacities. If you were to sit on your bike and imagine where the majority of your weight is resting you would notice that the motorcycle is set up in such a way that most of the weight of the rider is over the back half of the bike.
If you were to add luggage racks or saddlebags to your bike that weight would also be over the rear wheel. Very seldom does additional weight go over the front half of the bike. So the load capacity is most important on the rear tire.
Motorcycle tire load ratings go as low as 33 which is 254lbs and as high as 90 which is rated for 1,323lbs. Speed ratings go from J through Y with J being rated at 62mph and Y which can go all the way up to 186MPH.
You may see the letter Z or ZR on your tire. That means the tire is rated for equal to or greater than 149mph. You will see the Z or ZR designation on V, W, and Y-rated tires.
Why Is It Important To Use the Correct Tire?
The obvious reason you would want to make sure to use the correct size when replacing or changing your tire is that you want to make sure it fits. Trying to install the incorrect size tire could be as obvious as the tire just not fitting on the wheel, but using the wrong size tire could also compromise the safety of your bike.
It’s always best to consult your owner's manual if in doubt about what size tire is best for your ride. If you have aftermarket wheels, the wheel manufacturer can usually provide that information as well.
Correct speed and load rating are also important to consider when selecting a tire. In the case of a 77H-rated tire, we know that it can maintain a load of 908lbs at a maximum speed of 130mph. This is the type of wheel that you might see on a touring bike or a cruiser. Typically the use case for this type of tire would be a heavier bike that may be laden with saddle bags or luggage.
Where Can I Buy Motorcycle Tires?
The most reputable websites to purchase motorcycle tires from are going to be Revzilla and Cyclegear. When purchasing a tire online you can filter the results by tire size and make sure you are buying the right tire for your bike.
Always remember that your tires should be the only point of contact between the pavement and your bike so it is always critical to make sure that your tires are in good condition and mounted properly. While you can mount your tires at home only do so if you have the proper tools and understanding. An improperly mounted tire can be dangerous.
