Compare two setups
Setup A RPM–
Setup B RPM–
Difference–
Estimated RPM = mph × transmission ratio × transfer ratio × axle ratio × 336 ÷ tire diameter. Converter slip and actual tire diameter can change real results.
Reading the result
A numerically higher axle ratio raises engine RPM at a given road speed; a taller tire lowers it. The “right” result depends on engine, transmission, vehicle weight, elevation, intended speed, towing, and trail use.
Historical context
Axle ratios became a common Jeep-owner calculation as larger tires moved from specialized trail rigs into daily-driven Wranglers. Read the Dana and Spicer axle history and how the JK changed aftermarket expectations.