Built for 1992–1996 Gas and 1992–1997 Diesel Ford F-Series/Bronco with the factory 85 MPH cluster. Enter your tire size to estimate diameter, then calculate Revs/Mile ≈ 20168 ÷ Diameter. We apply Ford’s factor (108 for Bronco/F-150, 120 for F-250/F-350) to output your PSOM constant + entry number. Note: real tire diameter can vary by brand, tread, and pressure.