Tire & Gear Ratio Chart - Jeep 4x4 | Morris 4x4 Gear Ratio & Tire Size Chart. Considering making modifications to your Jeep? Whether it is changing an axle or going with different tires this chart is helpful in finding the right Tire Size to Gear Ratio that you need to achieve the optimal performance for your particular application. Gear Ratio Guide for Larger Tires | Quadratec Oct 09, 2019When ever you change tire size from the original size to another there will be a direct effect on power and drivability. We have developed this chart to help you select the optimum gear ratio to put your performance back where you want it. Using the chart below, first determine your original gear ratio and tire size and follow to the intersection that should be your approximate RPM at 65 MPH.