Motorcycle Tire Bible 2


In the last passage, we learned about the basic principles of a motorcycle tire. In passage 2 we are going to learn how to decipher those numbers on your tire.

Tires don’t age as a fine wine does, in fact, they expire after some time. To know when this expiration date is we have to look at those numbers that are written on your tire’s sidewall.

Your motorcycle tire sidewall contains a ton of information but only to those that know what those numbers and letters mean. Let’s take a look at an example 120/70 ZR17 M/C (58W)

Tire width

This number tells us the nominal width, measured in millimeters from sidewall to sidewall. In the case of our example it wold mean that the nominal width is 120mm. Note: the actual physical width of the tire on the rim can differ from the nominal width.

Aspect ratio

Is the next number in line this will indicate the height expressed as a percentage of the width. In case our case the aspect ratio is 70% of the 120MM width, making it 84mm.

Wheel diameter

Is the first two letters in a line. in the case of our example, the “Z” indicates the speed rating of the tire, which means it is rated above 240kph or 149mph. the “R” tells us about the construction of the tire. Do you remember the two construction types there are? indeed Radial and Bias tire’s, so the “R” stands for Radial. The “17” explains to us that the tire is 17 in diameter whilst “M/C” means that the is made for a motorcycle.

Load index and Speed rating

It should always be on your mind when buying a new tire. In this case, the ‘58’ tells us the tire is rated for a maximum carrying weight of 236kg at maximum pressure. The last in line is the “W” and this represents the maximum speed for the tire when it is correctly inflated and being used under load, in this case, 270km/h. Just remember that next time buying your motorcycle tire. You should always match the speed rating with the speeding capabilities. If exceeded, there is a big risk of tire failure.

How can I tell how old my tires are?

To know when it is time to celebrate your tire’s birthday we just have to look at one of the sidewalls of your tire. There you will find the ‘DOT’ (Department of Transport) code. In this code, the last four figures are the ones that tell us about the production date. The first two figures refer to the week that is was made, and the last two refer to the year of production. 

Deciphering the numbers, you may need to grab a calculator for this one. For example, a tire with the digits 2510 was made int the 25th week of 2010. instead of grabbing a calendar and counting out the weeks to determine the month, you can simply divide the number of weeks by 4,3. in this case, the tire would have been made in June 2010. To determine the age, you can subtract the manufacture date form the current date, with would make our example 2 years and 7 months old. 

Most experts use it as a general rule that the lifespan of a motorcycle tire should not exceed its 5th birthday. However, you can extend this to ten years. 

A good example of this case was when I was in the alps last summer. I did a tour of the alps, riding to all the big and small mountain passes in the area. I would total around 4000Km in 6 days. The days were hot and my driving was fast before I knew it I was in Italy and my rear tire was all the way spent. They looked like slicks with almost no tread on them what’s so ever!


I went form town to town in search of a motorcycle tire. I did find a rear tire that the owner of a Audi car garage had laying around. He told me it was 4 years old but always stored in a dark place. Indeed the numbers matched what he said. For me, it was even better. When a tire is left for some time the compounds harden out and you can get more mileage out of the tire. The only downside to that is you really have to take care when you go all out on those mountain passes. 

Post by Mister.T

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