How to Read Motorcycle Sidewalls
By Midwest Traction on September 7, 2017
Tips & Advice
Tires carry a wealth of information on their sidewalls. Unfortunately, much is in code and of little concern to the average tire owner. Our specialty tire readers, however, may find the knowledge useful.
Tire sizing uses three methods: Inch, Metric, & Alpha Numeric.
Mostly used for ATV tires, lawn tires, and some older motorcycle and automotive tires. Below is an ATV tire size at 25×8-12 or 25×8.00-12.
If this size says 25x8R12, the “R” indicates radial construction. Converted to metric, 25x8R12 looks like this:
Metric is now the automotive standard, as it depicts the most info. The motorcycle tire below is sized at 120/70ZR17.
Let's decode the numbers, first.
120 = tire width in millimeters, measured in a straight line through the tire from one edge of the tread to the other
70 = aspect ratio between width and height; or, how tall a tire is in relation to its width. The higher this number, the taller the tire. Here, the tire is 70 percent as tall as its width.
17 = rim diameter in inches.
Alpha Numeric Size
This older method, using letters and numbers, is most commonly found on Harley-Davidson and older Honda Gold Wings. Below is size MT90H16 (same as tire size 130/90H16).
M = designated for motorcycle use
T = tire width code
90 = aspect ratio
16 = rim diameter
In the old days, motorcycle tires weren't much bigger than an MV85, which corresponds to a 150mm width. What does this mean? Newer tires larger than 150mm only use metric sizing.
Speed Rating and Tire Construction
There are a few letters we haven’t discussed. In the metric example above, the letters “ZR” appear (120/70ZR17). In others, you may notice a separate set of numbers/letters at the end, like “180/55ZR17 73W” or “170/70B16 75H.”
The letters directly after the aspect ratio (where ZR appears) indicate speed rating and/or tire construction. If there are two letters, the first is for speed and the second denotes construction.
Speed Rating and Service Description
One letter or a dash (-) after the aspect ratio indicates that construction type and speed rating appear in the service description. Using MT90B16 74H, the service description is a combination of the load index (74) and the speed rating (H). The service description is “74H.”
The letter represents the speed rating. Each letter notes the maximum speed a tire can sustain under its recommended load capacity. Referencing the chart at right, V's maximum speed is 149 mph. Because this system was created in Europe, increments per letter are 10 kilometers per hour.
**Sometimes the letters Z and W or Y appear. W and Y are recent additions to the lettering system. When Z-speed rated tires were first introduced, the tire industry anticipated it representing the highest tire speed rating in excess of 149 mph (240 km/h). While Z speed-rated tires are capable of more than 149 mph, there's no end point noted. W and Y speed ratings were added to identify top-speed capability.
While a Z still often appears, it only signifies maximum speed capability in excess of 149 mph. The W in indicates actual maximum speed (168 mph or 270 km/h).
Here are some less common speed ratings, found in smaller-sized tires.
Load Index and Pressure Codes
The load index is the weight a tire can carry when properly inflated. Most manufacturers put the maximum load on the tire wall next to the maximum air pressure.
One of the biggest mistakes people make with their tires is filling past the indicated maximum level. This leads to poor handling and premature wear. Measure pressure when the tire is cold. Measuring hot skews the reading.
Below is a chart of common load indexes. We’ve included a more thorough chart at the end of this article for your reference.
Other Significant Markings
Rotation and Balance
The rotation arrow(s) is one of the more critical marks. Today’s specialized motorcycle tires have a tread pattern that must go in only one direction.
During the manufacturing process, tread rubber is initially a flat strip cut to length, at an angle, and spliced together with the two ends overlapping, which creates a hoop. Under acceleration, a tire mounted backward peels back this splice. The opposite is true for the front wheel, where directional forces are reversed under hard braking.
In some cases, it is acceptable to use a rear application tire on the front, but you must reverse the rotation. Never use a front application tire on the rear. (Always consult with your motorcycle manufacturer before reversing the rotation.) Best policy? Use a front motorcycle tire on the front and a rear motorcycle tire on the rear!
Look for painted balance dots when mounting a tire. Most are pre-balanced by the manufacturer and marked to indicate where the valve stem should line up. This is not always available on some tires, so it's good practice, but not critical. Place concern on finding the correct tire balance.
Born On Date and Tire Wear
Manufacturing date can be found on a raised block with four digits, usually located by the U.S. DOT tire identification number. The first two numbers indicate the week of manufacture; the second two for the year. Ex: 1702 = April 2002 or the 17th week of 2002. Prior to 2000, there were only three digits, with the last one indicating the year.
Some tires may have raised triangles, or the letters TWI, mark the tire wear indicators. When these are equal to the tread, it’s time for new tires.
Other information is usually spelled out. “Tubeless” or “tube type” may be substituted with the letters TL or TT. Tire ply, composition and materials used may also be spelled out.
As always, if you have questions or need help, please send us a message, or give us a call at 1-855-681-8326.
Oh, and here is that detailed load index chart we promised: