Selecting the right scooter parts can often be a challenging process for the first-time motor scooter owner. Of all the parts for scooter repair or replacement, few are as initially confusing as determining the correct scooter tire size for your rims. However, once you learn the 'secret code' of tire sizing, you should have no trouble selecting the right rubber for your street-legal machine.
Most of the confusion is due to two different systems in use concurrently; the older inch-pattern, and the newer, hybrid millimeter / inch system. A classic example of an inch-pattern scooter tire size is the 3.50-10. These are still very common on vintage Italian scooters, their modern clones and look-alikes. Simply read 3.50-10 as the inch measurement of the scooter's rim; in this case, 3-1 / 2 inches by 10 inches. Other popular inch-pattern sizes are 3.00-10 and 3.5-8.
The newer hybrid millimeter / inch coding is where it becomes a bit complicated. This will always read as three sets of numerals separated by a slash (the millimeters) and a hyphen (the inches). A typical example is the common size 120 / 70-10. The numbers before the slash (in this case 120) designates the width of the tire in millimeters when mounted and inflated. These two or three digits will range from about 80 to 160.
The two digits following the slash are called the Aspect Ratio, usually between 50 and 90, and are read as a percentage. Multiply the width (the number before the slash mark) by the aspect ratio number, and the result gives the tire's height between the rim bead and the tread. For example, multiplying 120 x.70 shows this tire has a height of 84 mm. The number following the hyphen represents the inch measurement of the rim diameter.
Thus a 120 / 70-10 tire would be 120mm wide, 84mm from tread to rim, and 10 inches from top to bottom of the rim. Buying the best rubber scooter parts becomes really simple when you learn to read the code.
Many of the early scooters from the 1950s and '60s, and many of today's retro-styled models, sported front and rear rims of the same size. Usually in an 8 or 10 inch diameter, these were the classic 'little wheels' of the Golden Age of scooterdom. Sharing an attribute with their larger motorcycle siblings, many contemporary scooters require a wider or even larger diameter tire on the rear wheel than on the front. This is most often the case with scooters bearing larger displacement engines; the 50 and 125cc powerplants of yesterday just did not require the same amount of rubber on the blacktop to ensure gyroscopic stability as today's 250cc maxi-scooters.
Most major scooter tire manufacturers such as Kenda and Michelin have fitment charts on their websites. Making matters simple as possible for the scooter owner; you can just search for your scooter's make and model, and then see just what rubber is made for it. Selecting the right rubber parts for scooter rims has never been so painless.