Gear Ratio Guide

Gear Ratio Guide for Larger Tires When 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. Good "rule of thumb" calculation is to mutiply .12 by your tire diameter. (.12 X 38" = 4.56) (see more formulas at bottom of page) 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. Next find your new tire size and follow that across to the closest RPM to your original and that will be first choice.  If you are interested in a change that will give more power or better fuel mileage use the color coding as a guide.   Highway Driving, Good Fuel Economy   Daily Driver, Best Overall Performance   Most Power and Towing, Reduced Fuel Economy This chart is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Please NOTE: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated. 2.35 2.73 2.94 3.07 3.21 3.31 3.42 3.55 3.73 3.91 4.11 4.27 4.56 4.88 5.13 5.29 5.38 5.71 6.17 7.17 22 2333 2710 2919 3048 3178 3286 3395 3524 3703 3882 4080 4239 4527 4845 5093 5252 5341 5668 6125 7118 23 2231 2592 2792 2915 3048 3143 3248 3371 3542 3713 3903 4055 4330 4634 4871 5023 5109 5422 5859 6808 24 2139 2484 2675 2794 2921 3012 3112 3231 3394 3558 3740 3886 4150 4441 4668 4814 4896 5196 5615 6525 25 2053 2385 2568 2682 2804 2892 2988 3101 3259 3416 3590 3730 3984 4263 4482 4621 4700 4988 5390 6264 26 1974 2293 2470 2579 2696 2780 2873 2982 3133 3284 3452 3587 3830 4099 4309 4444 4519 4796 5183 6023 27 1901 2208 2378 2483 2597 2677 2766 2872 3017 3163 3325 3454 3689 3947 4150 4279 4352 4619 4991 5800 28 1833 2129 2293 2395 2504 2582 2668 2769 2909 3050 3206 3331 3557 3806 4001 4126 4196 4454 4813 5593 29 1770 2056 2214 2312 2417 2493 2576 2674 2809 2945 3095 3216 3434 3675 3863 3984 4052 4300 4647 5400 30 1711 1987 2140 2235 2337 2410 2490 2584 2715 2846 2992 3109 3320 3553 3735 3851 3917 4157 4492 5220 31 1656 1923 2071 2163 2261 2332 2409 2501 2628 2755 2896 3008 3213 3438 3614 3727 3790 4023 4347 5051 32 1604 1863 2007 2095 2191 2259 2334 2423 2546 2669 2805 2914 3112 3331 3501 3610 3672 3897 4211 4894 33 1555 1807 1946 2032 2124 2191 2263 2349 2469 2588 2720 2826 3018 3230 3395 3501 3561 3779 4083 4745 34 1510 1754 1889 1972 2062 2126 2197 2280 2396 2512 2640 2743 2929 3135 3295 3398 3456 3668 3963 4606 35 1466 1704 1835 1916 2003 2065 2134 2215 2328 2440 2565 2664 2845 3045 3201 3301 3357 3563 3850 4474 36 1426 1656 1784 1862 1947 2008 2075 2154 2263 2372 2493 2590 2766 2961 3112 3209 3264 3464 3743 4350 37 1387 1611 1735 1812 1895 1954 2019 2095 2202 2308 2426 2520 2692 2881 3028 3123 3176 3370 3642 4232 38 1351 1569 1690 1764 1845 1902 1966 2040 2144 2247 2362 2454 2621 2805 2948 3040 3092 3282 3546 4121 39 1316 1529 1646 1719 1798 1854 1915 1988 2089 2190 2302 2391 2554 2733 2873 2962 3013 3198 3455 4015 40 1283 1491 1605 1676 1753 1807 1867 1938 2037 2135 2244 2331 2490 2664 2801 2888 2937 3118 3369 3915 41 1252 1454 1566 1635 1710 1763 1822 1891 1987 2083 2189 2275 2492 2599 2733 2818 2866 3042 3287 3819 42 1222 1420 1529 1596 1669 1721 1778 1846 1940 2033 2137 2220 2371 2538 2668 2751 2798 2969 3208 3728 43 1194 1387 1493 1559 1630 1681 1737 1803 1894 1986 2087 2169 2316 2479 2606 2687 2733 2900 3134 3642 44 1166 1355 1459 1524 1593 1643 1698 1762 1851 1941 2040 2119 2263 2422 2545 2626 2670 2834 3063 3559 Here are some common gear formulas: Gear Ratio Crawl Ratio P-Metric to Inch Diameter Tire Change (find new gear ratio) Speedometer Adjuster (with oversize tires) (New Tire Diameter / Old Tire Diameter) * Speedometer MPH = Actual MPH Simple Gear Ratio Formula Ring Gear Teeth Count / Pinion Gear Teeth = Gear Ratio