Dirt Bike Tire Sizing & How to Read Article on 4Strokes.com

Most dirt bike tires have a set of numbers that indicate the tire width, aspect ration (height) and rim diameter. Sometimes you might see just the tire width and diameter in inches (i.e. 2.50 - 10), and this is common with smaller tires.

Tire Sizing Example Using an 80/100-21 Front Tire

Using a common 80/100-21 rear tire as an example; the first number, 80, indicates the width of the tire in millimeters. The second number,100, is the aspect ratio, which is the height of the sidewall in relation to the width of the tread (100% of 80mm). The last number, 18, is the rim diameter in inches. So this tire is 80mm wide by 80mm high or tall and fits a 21" front rim.

Using a common 110/100-18 rear tire as an example; the first number, 110, indicates the width of the tire in millimeters. The second number,100, is the aspect ratio, which is the height of the sidewall in relation to the width of the tread (100% of 110mm). The last number, 18, is the rim diameter in inches. So this tire is 110mm wide by 110mm high or tall and fits an 18" rear rim.

Rear Dirt Bike Tire Sizing

Metric Alpha Inches

80/100 80/90 2.50/3.60

90/100 110/90 3.60/4.10

100/100 120/80 4.00/4.10

110/100 130/80 4.00/4.50

120/100 140/80 5.00/5.10

130/80 5.00-5.10

140/80 5.50-6.00

Front Dirt Bike Tire Sizing

Metric Alpha Inches

60/100 90/80 2.50/2.75

70/100 90/90 2.75/3.00

80/100 100/80 3.00/3.25

120/80 4.25-4.50

General Dirt Bike Tire Sizing

Engine Front Tire Rear Tire

50cc 2.50-10 2.50-10

70cc 2.50-14 3.00-12

80cc 2.50-16 3.60-14

100cc 2.5-19 3.00-16

200cc 80/100-21 100/100-17

250cc 80/100-21 100/100-18 | 100/90-19

400cc+ 80/100-21 110/100-18 | 110/90-19

Note: Above info provided as reference only. Always consult your owners manual for exact specifications and tire sizes.