Metric Tire Sizes (most commonly used for Motorcycle and many scooter tires):

Example: 120/70-12

The first number (120) is the width of the tire in millimeters. This always refers to the measurement from sidewall to sidewall.

After the slash mark, the number you see (70) is for the tire’s aspect ratio. This number tells you how tall your tire’s profile is in a percentage. The aspect ratio is calculated by dividing a tire’s height off the rim by its width. If a tire has an aspect ratio of 70, it means that the tire’s height is 70% of its width. Lower aspect ratios generally offer vehicle handling performance advantages over higher aspect ratio tires but the tradeoff is a harsher ride.

The last number after the dash (12) is the diameter, in inches, of the rim onto which the tire can be mounted. The tire size that we are using for our example would fit a 12 inch rim.

Metric Tire Sizes also have a Load Index and Speed Index. The Load Index indicates the load, in pounds, that the tire can support when fully inflated. The number ranging from 1 to 150 corresponds to a carrying capacity ranging from 99 lbs. to 7,385 lbs.

The Speed Rating is indicated by a letter. This letter indicates the maximum speed that a tire can be used based on maximum load and inflation.

Numeric Tire Sizes (mostly used on Dirt Bike, Vintage and Scooter Tires):

Example: 3.50-10

The first number (3.50) is the tire width in inches. In most cases, this will also indicate that the profile of the tire (sidewall) is 3.50 inches too.

The second number (10) is the rim diameter in inches.

Some Numeric Tire Sizes will also have Speed/Load Index ratings if they are for street use. See above for further details on Speed and Load Index.

Bicycle Tire Sizes:

Example: 26x2.10

The first number (26) is the total outside diameter of the tire in inches including treads. This differs from most scooter and motorcycle diameter measurements which are usually focused on the Rim

ATV Tire Sizes (Standard):

Example: 19x7-8

The first number (19) is the total outside diameter of the tire in inches when mounted and inflated to the recommended air pressure. This can also be called the overall height of the tire.

The second number (7) is the overall width of the tire in inches when mounted and inflated to recommended air pressure.

The third number (8) is the diameter of the rim in inches that your ATV tire will mount on.

Small Electric Scooter Tire and Recreational Scooter Tire Sizes:

There is no standardization for small electric scooter and toy/recreational tire sizes. You can find a mix of the above tire sizing rules applied to these small sizes. Some sizing is in millimeters while some is in inches. Due to this inconsistency, your best bet is just to make sure that you order the same size that your scooter is currently running. Some common small scooter sizes are as follows:

200x50: 200 is the outer diameter in millimeters and 50 is the width in millimeters

3.00-4: 3.00 is the sidewall height in inches and 4 is both the rim size and the tire width in inches

9x3.50-4: 9 is the outer diameter, 3.50 is the width and 4 is the rim size all in inches

12 ½ x 2 ¼: 12 ½ is the outer diameter in inches and 2 ¼ is the width in inches