A tool used to determine the effects of changing tire dimensions or drivetrain gearing on a vehicle’s performance characteristics. It computes the relationship between engine revolutions, transmission gears, differential gearing, and rolling circumference of the tires to project vehicle speed at a given engine RPM. For example, by inputting current gear ratios and tire size along with proposed modifications, one can anticipate the shift in vehicle speed at a specific RPM.
This calculation is vital for optimizing vehicle performance based on intended use. Altering tire diameter or final drive ratio affects acceleration, fuel economy, and top speed. Understanding these consequences is crucial for applications ranging from off-road modifications requiring increased torque to fuel-efficient highway driving benefitting from lower engine RPMs at cruising speeds. Early iterations of this assessment relied on manual calculations, while modern versions provide streamlined digital interfaces.