Ever wonder what all those numbers and letters on the side of your otherwise pristine motorcycle tires are really there for? There is a wealth of information molded onto your moto’s meats. Look closely and you can discover where and when your tire was manufactured. Keep looking and the tire will tell you if it wants to spin in a particular direction. Lots of letters, numbers, and even the occasional symbol decorate modern tires. Some are obvious, like the manufacturer’s name, trademark, model, maximum load, and pressure. Other markings, such as “TWI,” might leave some wondering.
I find, for the most part, that motorcyclists tend to know much more about their vehicles than do those who drive only cars. Most (car-only) driving folks I know are aware of the tire size markings, but very few really know how they all relate to the tire’s actual size. With tire performance being so important to rider safety and bike handling, knowledge of tires helps greatly when selecting new rubber. Knowing the language on the side helps make sure we are informed consumers and install exactly the right tire for the needs of both the rider and the machine.
I took a size from the rear tire of one of my bikes to explain what it means: 150/70 R 17 M/C 69 V. Let’s start with the first three digits. “150” relates to the tire’s Nominal Section Width, and in this case it’s about 150 millimeters. If it read “190” it would be about 190mm wide and so on. The “70” relates to the tire’s sidewall height and is expressed as a percentage of the tire’s width. In other words, the sidewall height is 70 percent of the tire’s width. Next there is an “R” signifying the type of construction. “R” means it is a Radial tire. The letter “B” would indicate Bias Belted and a dash (-) simply a Bias tire. It is worth mentioning that you should ensure the front and rear tires are of the same type of construction as Bias ply tires handle differently than do radials. The rides can differ as well. It is important that the front and rear tires perform predictably in a similar manner. The next number is “17”, which is the wheel’s rim size expressed in inches. Following that is “M/C”, which is how the manufacturer lets you know this tire is designed for motorcycles. Then comes “69”. This is the tire’s load capacity. Load index charts are easy enough to find online, though I just happen to know that 69 is rated for 716 pounds when set at the psi indicated elsewhere on the tire. Then “V” follows the load index. “V” is the letter that expresses this tire’s Speed Rating and it is good up to 149 mph. Again, there are charts listing these online.
Your tire also has a “DOT” marking on it if it is DOT approved for highway use. There should also be other numerals following the “DOT” indication. These are the serial numbers of your tire. Next to that should be three or four numbers that indicate the week and year your tire was manufactured. So, if you find 4511, you know that your tire was born on the 45th week of 2011. When I’m paying for tires, I don’t want some that have been sitting in the back of a warehouse or cycle shop forever. There are also markings letting us know where the tire was made, materials comprising the plies, number of plies, and importantly, if the tire requires a tube or is tubeless.
Contemporary tires have many markings, symbols and words that all provide valuable information. We are fortunate that modern tires have amazing performance throughout most tire lines when compared to tires available just a decade ago. Look around, and one might be amazed at what is available. But, what IS TWI? TWI stands for Tread Wear Indicator. Look on the tread near that marking and you’ll see a raised area on the surface of the tire between the tread. When the tread has worn and becomes even (or close) to the TWI, the tire has reached the end of its designed service life. Pretty clever, huh?