For motocross tires, Dunlop changed to the industry tire standards in the same manner as street tires. However, because of the prior variations in actual dimensions, some adjustments in vehicle application have been necessary.
- When motorcycle tire standards for width, diameter and load capacity were introduced a few years ago, they didn’t include motocross tires. As a result, motocross tires varied in dimensions from one manufacturer to another. Most tire manufacturers marked their motocross tires with a size designation that related to tread width.
- In current tire standards, the designation for width is actually the section width, measured at the sidewall, not at the tread. This has always applied to street tires. A 4.50-18 street tire, for example, would have a section width of 4.50 inch, and would fit on an 18 inch rim.
- When metric tires were introduced, the aspect ratio was included in the size marking. A 130/80-18 street tire had a section width of 130mm, and an aspect ratio of 80 percent. This means that the height of the tire is 80 percent of 130mm. As before, the tire fits on an 18-inch rim.
- For motocross tires, Dunlop changed to the industry tire standards in the same manner as street tires. However, because of the prior variations in actual dimensions, some adjustments in vehicle application have been necessary. An off-road machine that previously fitted a 4.50-18 or 130/80-18 under the non-standards markings, now fits a 110/100-18 under the new standards. These tire sizes share the same actual dimensions. A 130/80-18 is 110 mm wide in section width and, furthermore, the section height is also 110 mm or 100-percent aspect ratio. Hence, a 130/80-18 under the new standards markings is designated a 110/100-18.
- With the introduction of 19 inch motocross sizes, it was necessary to reduce the aspect ratio in order to maintain the same outside diameter. To compensate for the additional inch in rim diameter (18 inch to 19 inch) fitted to a 250cc machine for example, the size would change from a 110/100-18 to a 110/90-19. The resulting low profile 19 inch tires with shorter sidewalls have provided improved stability performance, while retaining the same outside tire diameter.
- Building on the success of the 19 inch rear tire, Dunlop in the mid 1990’s became the first tire manufacturer to develop wider, lower profile motocross rear tires. The technology in the 110/80-19 & 120/80-19 creates a larger footprint for enhance traction and bump absorption. In the late 1990’s, Dunlop introduced a wider 90/100-21 front tire to compliment the rears. In each case, these wider, low-profile tires fit on existing standard-size rim widths, eliminating the need to replace rims.