Aspect ratio is the ratio of the tire's section height to its section width and is sometimes referred to as the tire "series" (IMAGE 1) . Therefore, a 50-series tire means one with an aspect ratio of 50%.
The resulting figure is stamped on all tires as part of the sizing information (IMAGE 2) The actual dimensions of a tire depend on the rim on which it is mounted. The biggest variable is the tire's section width; a change of about 0.2" for every 0.5" change in rim width. The ratio between the section width and the rim width is pretty important. If the rim width is too narrow, you pinch the tire in and cause it to balloon more in cross-section. If the rim width is too wide, you run the risk of the tire ripping away at high speed.
For 50-series tires and above, the rim width is 70% of the tire's section width, rounded off to the nearest 0.5. For example, a 255/50R16 tire has a design section width of 10.04" (255mm = 10.04 inches). 70% of 10.04" is 7.028", which rounded to the nearest half inch, is 7". Ideally then, a 255/50R16 tires should be mounted on a 7x16 rim. For 45-series tires and below, the rim width is 85% of the tire's section width, rounded off to the nearest 0.5.
For example, a 255/45R17 tire still has a design section width of 10.04" (255mm = 10.04 inches). But 85% of 10.04" is 8.534", which rounded to the nearest half inch, is 8.5". Ideally then, a 255/45R17 tire should be mounted on an 8½x17 rim. If your tire is narrower than the rim, according to rim calculator, RIM RINGZ™ will NOT fit properly, and it could fall off the rim
The "7JJ x 18" part of that is the size of the wheel rim - in this case it has a depth of 6 inches and a diameter of 14 inches. Those information you can find on each wheel (outside or inside wheel). On most aftermarket wheels, they don't want to pollute the lines and style of the outside of the wheel with stamped-on information - it's more likely to be found inside the rim, or on one of the inner mounting surfaces.
Given all the information above, you need to know one last thing. A rim that is too narrow in relation to the tire width will allow the tire to distort excessively sideways under fast cornering. On the other hand, unduly wide rims on an ordinary car tend to give rather a harsh ride because the sidewalls have not got enough curvature to make them flex over bumps and potholes. That's why there is a range of rim sizes for each tire size in Rim Ringz™ Rim calculator. If you install a 225/40R18 tire on a rim narrower than 7.5 inches or wider than 9 inches, you might experience undesired results.
If your tire is narrower than the rim according to Rim Ringz™ Rim calculator and Rim Ringz™ will not fit properly, then Rim Ringz™ could fall off the rim. The tire size is the most important thing for the proper use of Rim Ringz™. Rim Ringz™ is designed according to tire and wheel standards.
Also, if your tire is wider than the recommended size for your particular rim, the tire could lose some air. Any deviation from the recommended size for your particular rim can have a negative impact on Rim Ringz™ and it could fall off the rim. Even if at first it seems that Rim Ringz™ will fit the rims, but the tire size does not match the wheel size, we recommend you do NOT install Rim Ringz™.