Actual results may vary. According to the Technology & Maintenance Council (TMC) S.2 Tire & Wheel Study Group, improper tire inflation, defined as little as 10 psi low, reduces fuel economy by about one percent, increases total tire-related costs by approximately $600 to $800 annually per tractor-trailer combination, and changes the tire contact patch which affects stopping and acceleration traction and vehicle handling thereby impacting vehicle safety.