Gear Ratio Chart: Step-by-step

Simple guide to choosing the best diff gear ratios for your Jeep or 4x4 truck

I often get questions like:

What is the best gear ratio for 37 inch tires?
What gear ratio do I need for 35 inch tires?
What does a 1:1 gear ratio mean?
What diff gear ratio is best for fuel economy?
What is the best rear end gear ratio for my Chevy Silverado?
What axle ratio gears should I run with for 38 inch tires on my 4x4 Ford F-150?

If you are planning on 35" or 37" or even bigger tires for your Jeep or 4x4 truck this guide will show you the best ratio to choose. In this gear ratio guide you'll find the formulas and a simple chart that shows how you should lower your ring and pinion gear ratio.

1:1 Gear Ratio

The gear ratio of 1:1 means that the driven gear rotates at the same speed as the driving gear and is usually true for the ratio between the engine and the transmission when it is in 4th gear in a manual transmission. Going higher and you are in overdrive where the output of the transmission is revolving faster than the engine's output.

Differential Gear Ratio

The gear ratio most interesting to 4x4 truck owners is the ratio between the driveshaft and axles - the differential gear ratio or axle gear ratio. It is controlled by the number of teeth on the ring vs. the pinion. A ratio of 4.56 means that as the axle turns one whole circle the driveshaft turns 4.56 circles. The higher the number the lower the ratio becomes.

Chart Gear Ratio

The correct axle gear ratio is important for drivability and economy. When you increase the tire size without changing the gear ratio you increase fuel consumption and you can not drive at the low speeds needed for the off roads.

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.

For calculating this formula on-line go to the Tire Size Calculator.

An Old Axle Gear Ratio Formula

To calculate the rotations pr. minute of the engine you can use this formula.

This formula is for 4x4's with a 1:1 final drive ratio (no overdrive). It should work fine for manual transmission as well as an automatic when they are not in overdrive.

	MPH x Gear Ratio x 336
RPM =	―――――――――――――
	Tire Size

Example:

Adding to the last example. You usually start with 65 MPH, since that is the natural highway speed, multiply by 3.91 and then again with 336, dividing all by 30 gives you the before RPM of 2846. Calculating for the after ratio of 4.88 gears and 38" tires gives the RPM of 2805.

A 4x4 Differential Gear Ratio Chart Table

To sum it all up it can be handy to use this table for both your front and rear axle gear ratio selection. It is based on the above formula. You can use it to quickly estimate your trucks best gear ratio.

Tire
Size	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
30	2410	2490	2584	2715	2846	2992	3109	3320	3553	3735	3851	3917	4157	4492	5220
31	2332	2409	2501	2628	2755	2896	3008	3213	3438	3614	3727	3790	4023	4347	5051
32	2259	2334	2423	2546	2669	2805	2914	3112	3331	3501	3610	3672	3897	4211	4894
33	2191	2263	2349	2469	2588	2720	2826	3018	3230	3395	3501	3561	3779	4083	4745
34	2126	2197	2280	2396	2512	2640	2743	2929	3135	3295	3398	3456	3668	3963	4606
35	2065	2134	2215	2328	2440	2565	2664	2845	3045	3201	3301	3357	3563	3850	4474
36	2008	2075	2154	2263	2372	2493	2590	2766	2961	3112	3209	3264	3464	3743	4350
37	1954	2019	2095	2202	2308	2426	2520	2692	2881	3028	3123	3176	3370	3642	4232
38	1902	1966	2040	2144	2247	2362	2454	2621	2805	2948	3040	3092	3282	3546	4121
39	1854	1915	1988	2089	2190	2302	2391	2554	2733	2873	2962	3013	3198	3455	4015
40	1807	1867	1938	2037	2135	2244	2331	2490	2664	2801	2888	2937	3118	3369	3915
41	1763	1822	1891	1987	2083	2189	2275	2429	2599	2733	2818	2866	3042	3287	3819
42	1721	1778	1846	1940	2033	2137	2220	2371	2538	2668	2751	2798	2969	3208	3728
43	1681	1737	1803	1894	1986	2087	2169	2316	2479	2606	2687	2733	2900	3134	3642
44	1643	1698	1762	1851	1941	2040	2119	2263	2422	2546	2626	2670	2834	3063	3559
45	1606	1660	1723	1810	1898	1995	2072	2213	2368	2490	2567	2611	2771	2995	3480
46	1572	1624	1685	1771	1856	1951	2027	2165	2317	2436	2512	2554	2711	2929	3404
47	1538	1589	1650	1733	1817	1910	1984	2119	2268	2384	2458	2500	2653	2867	3332
48	1506	1556	1615	1697	1779	1870	1943	2075	2220	2334	2407	2448	2598	2807	3262
49	1475	1524	1582	1663	1743	1832	1903	2032	2175	2287	2358	2398	2545	2750	3196
50	1446	1494	1551	1629	1708	1795	1865	1992	2132	2241	2311	2350	2494	2695	3132
51	1417	1465	1520	1597	1674	1760	1829	1953	2090	2197	2265	2304	2445	2642	3070
52	1390	1436	1491	1567	1642	1726	1793	1915	2050	2155	2222	2260	2398	2591	3011
53	1364	1409	1463	1537	1611	1694	1760	1879	2011	2114	2180	2217	2353	2543	2955
54	1339	1383	1436	1509	1581	1662	1727	1844	1974	2075	2140	2176	2309	2495	2900

Choose lower numbers for better economy and highway usage and higher numbers for towing and better off road capabilities.

Get your ring and pinion gear ratio today!

4.88 Gears for sale today!

Offroad Tire Size Calculator

Tire Size Calculator helps in your decision making while planning modifications for your newest project.

How to select the perfect 4x4 offroad tire?

Belief it or not, after the truck it self, the off road tires along with the appropriate wheels are the most important ingredient to a good usable 4x4!

Lifting your 4x4 truck is what you need when fitting the big tires and wheels. Custom modified and lifted 4x4 trucks are less subject to damage in situations like river crossing and rocky trails.

Thrandur Arnthorsson

Thrandur is the chief-editor and owner of 4x4 Off Roads and an 4x4 off road enthusiast. Living in Iceland he loves to share the coolest 4x4 trucks and supporting more offroad freedom. If you want to get YOUR 4x4 featured on 4x4OffRoads you can post your story here.