Rear gears, tire size and highway RPM explained
A gear ratio that feels great leaving a light can get old after an hour on the interstate.
Understand the tradeoff
Numerically higher axle ratios increase torque multiplication, but also increase engine RPM at a given road speed if tire diameter and transmission ratio stay the same. Overdrive can reduce cruise RPM.
Calculate before ordering
Our calculator uses RPM = MPH × axle ratio × transmission ratio × 336 ÷ tire diameter in inches. It is a theoretical approximation. Torque-converter slip, actual tire rolling diameter and measurement error affect the real result.
Use real tire measurements
A nominal tire size gives an estimated unloaded diameter. Manufacturer dimensions and measured rolling circumference are better inputs. Do not assume two tires with the same labeled size roll identically.
Choose for the entire drivetrain
Consider engine operating range, transmission, vehicle weight, intended use and tire clearance. Gear setup and driveshaft work require proper tools and expertise. The calculator does not confirm mechanical fitment or a safe engine speed.
Reference: Manufacturer technical information ↗