Unit: Imperial Imperial Metric
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Rim Diameter 18.00 in
Rim Width Range 7.50 in - 9.50 in
Overall Diameter 32.07 in
Sidewall Height 7.04 in
The two easiest ways are to check the sticker plate in your car, it should be located inside the driver side door, or look online for the vehicle specifications for your exact make and model. That should tell you the standard rim size.
How do I know what size rims will fit my tires?
For sports cars, the general rule of thumb is to match the wheel width to the tread width in inches. For example a tire size 285/35-19 has a tread width of 9.9". The ideal wheel width would be 10.0" for that tire.
305/65R18 tires have a diameter of 33.6", a section width of 12.0", and a wheel diameter of 18". The circumference is 105.5" and they have 600 revolutions per mile. Generally they are approved to be mounted on 8.5-11" wide wheels.