Differential Gear Ratio to Tire Size Guide

How Tire Size & Gear Ratio Combos Affect Fuel Economy & Performance

BIG MEATS

This page is a Differential Gear Ratio Chart for comparing tire size to axle gear ratio and the combined effect on power and fuel economy.

About this Engine RPM / Tire Size chart:

The following chart of Tire sizes and axle gear ratios are meant to give a general idea of the relationship between the differential gear ratio and the tire size and what effect the ratio has on power output and fuel economy. The chart is based on RPM levels at 65 mph (105 kph) and a drive train running at a 1:1 gearing ratio, meaning the transmission and transfer case are passing power straight through at a one to one ratio without reducing or overdriving the engines rotations per minute before it reaches the differential. It is also worth noting that a manual transmission will be the most efficient at transferring power through to the axles and that an automatic transmission will have some inherent slippage without a locking torque converter. Also with an overdrive transmission, your engine RPM will be approximately 20 to 30% less than shown here depending on the overdrive ratio.

  
 
Good Fuel Economy but less power, good for flat highway driving
  
 
Best Overall Performance, good for daily driving
  
 
Highest for Power and Towing but reduced fuel economy, higher engine RPM
Tire
Size

DIFFERENTIAL GEAR RATIO 2.94 – 4.27

2.94
3.07
3.21
3.31
3.42
3.55
3.73
3.91
4.11
4.27
28
2293
2395
2504
2582
2668
2769
2909
3050
3206
3331
29
2214
2312
2417
2493
2576
2674
2809
2945
3095
3216
30
2140
2235
2337
2410
2490
2584
2715
2846
2992
3109
31
2071
2163
2261
2332
2409
2501
2628
2755
2896
3008
32
2007
2095
2191
2259
2334
2423
2546
2669
2805
2914
33
1946
2032
2124
2191
2263
2349
2469
2588
2720
2826
34
1889
1972
2062
2126
2197
2280
2396
2512
2640
2743
35
1835
1916
2003
2065
2134
2215
2328
2440
2565
2664
36
1784
1862
1947
2008
2075
2154
2263
2372
2493
2590
37
1735
1812
1895
1954
2019
2095
2202
2308
2426
2520
38
1690
1764
1845
1902
1966
2040
2144
2247
2362
2454
39
1646
1719
1798
1854
1915
1988
2089
2190
2302
2391
40
1605
1676
1753
1807
1867
1938
2037
2135
2244
2331
41
1566
1635
1710
1763
1822
1891
1987
2083
2189
2275
42
1529
1596
1669
1721
1778
1846
1940
2033
2137
2220
43
1493
1559
1630
1681
1737
1803
1894
1986
2087
2169
44
1459
1524
1593
1643
1698
1762
1851
1941
2040
2119

 

Tire
Size

DIFFERENTIAL GEAR RATIO 4.27 – 5.71

4.27
4.56
4.88
5.13
5.29
5.38
5.71
28
3331
3557
3806
4001
4126
4196
4454
29
3216
3434
3675
3863
3984
4052
4300
30
3109
3320
3553
3735
3851
3917
4157
31
3008
3213
3438
3614
3727
3790
4023
32
2914
3112
3331
3501
3610
3672
3897
33
2826
3018
3230
3395
3501
3561
3779
34
2743
2929
3135
3295
3398
3456
3668
35
2664
2845
3045
3201
3301
3357
3563
36
2590
2766
2961
3112
3209
3264
3464
37
2520
2692
2881
3028
3123
3176
3370
38
2454
2621
2805
2948
3040
3092
3282
39
2391
2554
2733
2873
2962
3013
3198
40
2331
2490
2664
2801
2888
2937
3118
41
2275
2492
2599
2733
2818
2866
3042
42
2220
2371
2538
2668
2751
2798
2969
43
2169
2316
2479
2606
2687
2733
2900
44
2119
2263
2422
2545
2626
2670
2834

 

1 Comment

  1. I have an 1986 Jeep Comanche2.5L I4 with % speed manual Transmission and a 4.11. I only get 14 to 16 mpg at 55mph and an rpm of 2600 at 60 mph my rpm is 2900. what would be the best thing to do to get better mileage. The window sheet says I should get between 22 to 26 mpg.

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