This calculator is offered as a tool in helping to determine proper air pressure for alternative tire sizes. Never use a pressure lower than that specified by the vehicle manufacturer. The vehicle manufacturer will determine air pressure based on many factors such as ride quality, fuel efficiency, performance and load capacity. The calculation offered here is only for determining air pressure required to support the GAWR of the vehicle. For an original equipment size, use the vehicle manufacturers required air pressure. Results assume the tire is mounted on a wheel within the approved rim width range. The system cannot account for other modifications made to a vehicle which would increase the required load carrying capacity. If the selected vehicle and tire combination results in the required load exceeding the tires rated capacity, an error message may be displayed. Such a tire size is not recommended for the selected vehicle and would not be covered by Atturo’s standard warranty.