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Gear Ratio Guide

A simple formula

The most simple formula for the correct gear ratio is this:

	New Tire Size x Old Gear Ratio
New Gear Ratio =	―――――――――――――――――
	Old Tire Size

Example:

The original tire size is 30" and the original gear ratio is 3.91. You plan on moving up to 38". Then the formula would be calculated as: (38*3.91)/30 giving you 4.95. Not all gear ratios are available so you have the choice between 4.88 and 5.13, 4.88 being the closest.

Choose a little bit lower gear ratios if you do a lot of off-road driving and a little bit higher if you do more long distance highway trips.

This chart is based on 65 MPH and a 1:1 gear ratio, on manual transmission (4th gear). Please NOTE: If your vehicle is equipped with an automatic transmission the RPM wil be higher than shown on the chart, because some slippage will occur in the transmission and torque converter. With overdrive transmission, your RPM in overdrive will be 15 - 30% less than indicated, depending on the vehicle.

RPM Chart

Gear Ratio
Tire Size		2.73	3.07	3.55	3.73	4.11	4.27	4.56	4.88	5.13	5.29	5.38	5.71
	28"	2129	2395	2769	2909	3206	3331	3557	3806	4001	4126	4196	4454
	29"	2056	2312	2674	2809	3095	3216	3434	3675	3863	3984	4052	4300
	30"	1987	2235	2584	2715	2992	3109	3320	3553	3735	3851	3917	4157
	31"	1923	2163	2501	2628	2896	3008	3213	3438	3614	3727	3790	4023
	32"	1863	2095	2423	2548	2805	2914	3112	3331	3501	3610	3672	3897
	33"	1807	2032	2349	2489	2720	2826	3018	3230	3395	3501	3561	3779
	34"	1754	1972	2280	2396	2640	2743	2929	3135	3295	3398	3456	3668
	35"	1704	1916	2215	2328	2565	2664	2845	3045	3201	3301	3357	3563
	36"	1656	1862	2154	2263	2493	2590	2766	2961	3112	3209	3264	3464
	37"	1611	1812	2095	2202	2426	2520	2692	2881	3028	3123	3176	3370
	38"	1569	1784	2040	2144	2362	2454	2621	2805	2948	3040	3092	3282
	39"	1529	1719	1988	2089	2303	2391	2554	2733	2873	2962	3013	3198
	40"	1491	1676	1938	2037	2244	2331	2490	2664	2801	2888	2937	3118
	41"	1454	1635	1891	1987	2189	2275	2429	2599	2733	2818	2866	3042
	42"	1420	1596	1846	1940	2137	2220	2371	2538	2668	2751	2798	2969
	43"	1387	1559	1803	1894	2087	2169	2316	2479	2606	2687	2733	2900
	44"	1355	1524	1762	1851	2040	2219	2263	2422	2546	2626	2670	2834

	Highway Driving, Good Fuel Economy
	Daily Driver, Best Overall Performace
	Towing and Power, Reduced Fuel Economy

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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.

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.

Tire
Dia.

Gear Ratio

	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

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