How to figure your final drive ratio or crawl ratio.  
  If you have changed to over sized tires you have probably noticed that your gearing has become higher. Changing the gears inside your differentials can help get your engine running back within its proper power band for street applications. For best off road low range crawling you may want to consider a 4 to 1 (4:1) kit for your transfer case. Your  final drive or crawl ratio should be at least be between 50 to 1 (50:1) and 70 to 1 (70:1) for best rock crawling performance. 

Final drive ratio or crawl ratio is figured by multiplying your transmission 1st gear ratio, transfer case low range gear ratio and differential gear ratio.

Let's use some typical ratios to show the end result.

AX15 transmission has 1st gear ratio of 3.83
NP231 Transfer case low range ratio of 2.72
Differential gear ratio of 4.10

3.83 X 2.72 X 4.10 = 42.71

Rounding the number off to the nearest whole number equals 43 to 1 or 43:1

Jeep Model Transmission Transfer case Axle  Ratios
4 Cyl. YJ & TJ
AX5 Manual 5 speed
1st  3.93
2nd  2.33
3rd  1.45
4th  1.00
5th  0.85
NP231
2.72
 
With 4:1 Kit
3.93
Front Dana 30
Rear Dana 35

NOTE: I have not seen 4 Cyl. equipped Jeep with anything but 4.10 gears from factory.
3.07 Factory
3.55 Factory
3.73 Factory
4.10 Factory
4.56 Aftermarket
4.88 Aftermarket
(See axle tag on differential cover for factory ratio)
6 Cyl. YJ & TJ
AX15 Manual 5 speed
1st  3.83
2nd  2.33
3rd  1.44
4th  1.00
5th  0.79
NP231
2.72
 
With 4:1 Kit
3.93
 
Front Dana 30
Rear Dana 35

Optional  Rear Dana 44 on TJ only.
For 30 and 35 see above

Dana 44

3.07 Factory
3.55 Factory
3.73 Factory
4.10 Factory
4.56 Aftermarket
4.88 Aftermarket
5.13 Aftermarket
6 Cyl. YJ & TJ
32RH Automatic 3 speed
1st  2.74
2nd  1.54
3rd  1.00
NP231
2.72
 
With 4:1 Kit
3.93
 
Front Dana 30
Rear Dana 35

Optional  Rear Dana 44 on TJ only.
For 30 and 35 see above

Dana 44

3.07 Factory
3.55 Factory
3.73 Factory
4.10 Factory
4.56 Aftermarket
4.88 Aftermarket
5.13 Aftermarket
CJ
Not available.
Typical first gear would be 3.10 to 3.50
Dana 18 recognized by the off set to the passenger side.
2.46
With 4:1 kit
3.15
Dana 20 Centered, internal parts interchangeable with Dana 18
2.03
With 4:1 kit
3.15
Dana 300
2.62
Refer to Axle Application Guide
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