It is measured from the wheel rim to the top of the tread. In the example above, the 18-inch tires would have a sidewall height of 60% of the tread width. 60% of 215mm is 129mm. 18 Inch Wheels
are larger, so they could fit bigger brakes to your off-roader. The larger tires can improve the towing capability of the vehicle. As they have shorter sidewalls, it affords stable handling for on-road driving.