Jeep Speed Calculator

Instructions: The calculator is preloaded with some typical values. To see the speed with other values, click buttons on the lists of common values provided, and watch the speed change. Or fill-in numbers directly in the blanks, and when the cursor leaves the input box, the speed will be recalculated.

Tire size

26"
27"
28"
29"
30"
31"
32"
33"
34"
35"
36"
37"
38"
39"
40"
42"

 Axle Gears

5.89:1 (53/9)
5.38:1 (43/8)
4.89:1 (44/9)
4.56:1 (50/11)
4.27:1 (47/11)
4.09:1 (45/11)
3.92:1 (47/12)
3.73:1 (41/11)
3.54:1 (46/13)
3.31:1 (43/13)
3.07:1 (43/14)
2.94:1 (47/16)
2.72:1 (41/15)

 Transmission

3 Speeds

T90
R 3.798
1st 2.798
2nd 1.551
3rd 1.00

T90C
R 3.798
1st 3.34
2nd 1.85
3rd 1.00

T86
R 3.79
1st 2.79
2nd 1.68
3rd 1.00

T14
R 3.10
1st 3.10
2nd 1.61
3rd 1.00

T15
R 3.00
1st 3.00
2nd 1.83
3rd 1.00

T150
R 3.17
1st 2.99
2nd 1.75
3rd 1.00

Truck 4 Speeds

T98/T18/T19
R 7.44
1st 6.32
2nd 3.09
3rd 1.69
4th 1.00

T18 4:1
R 4.73
1st 4.02
2nd 2.41
3rd 1.41
4th 1.00

NP435
R 8.26
1st 6.68
2nd 3.34
3rd 1.74
4th 1.00

SM420
R 6.78
1st 7.06
2nd 3.58
3rd 1.71
4th 1.00

SM465
R 6.09
1st 6.55
2nd 3.58
3rd 1.57
4th 1.00

Light Duty 4 Speeds

Muncie M20 Wide Ratio
R 3.56
1st 2.52
2nd 1.88
3rd 1.46
4th 1.00

Muncie M21 Close Ratio
R 2.27
1st 2.20
2nd 1.64
3rd 1.28
4th 1.00

Jeep T-4
R 3.76
1st 4.03
2nd 2.37
3rd 1.50
4th 1.00

RTS Overdrive
R 3.25
1st 3.25
2nd 1.92
3rd 1.00
4th 0.78

T-176
R 3.52
1st 3.52
2nd 2.29
3rd 1.46
4th 1.00

5 Speeds

AX15
R 4.76
1st 3.83
2nd 2.33
3rd 1.44
4th 1.00
5th 0.79

NV-3550
R 3.57
1st 4.01
2nd 2.33
3rd 1.39
4th 1.00
5th 0.78

Jeep T-5
R 3.76
1st 4.03
2nd 2.37
3rd 1.50
4th 1.00
5th 0.86

TR4050
R 6.03
1st 6.16
2nd 3.11
3rd 1.71
4th 1.00
5th 0.76

NV4500
R 5.61
1st 6.34
2nd 3.44
3rd 1.71
4th 1.00
5th 0.73

6 Speeds

NSG370
R 4.06
1st 4.46
2nd 2.61
3rd 1.72
4th 1.25
5th 1.00
6th 0.84

Ahead of Tcase Doubler/OD

Novak Novadrive

normal 1.00
od 0.76

NP203 Doubler

high 1.00
low 1.96

D300 Strongbox Doubler

high 1.00
low 2.72

 Transfer Case

Dana 18
hi 1.00
low 2.46
Terra low 3.15
JPet low 5.13

Dana 20
hi 1.00
low 2.03
Terra low 3.15

BW1339 Quadratrac
hi 1.00
low 2.57

NP231/NP242
hi 1.00
low 2.72

Rubicon NP241OR
hi 1.00
low 4.00

Dana 300
hi 1.00
low 2.62
LoMax 4.00

Atlas Options
hi 1.00
low 3.00
low 3.80
low 4.30
low 5.00

Rover LT230
hi 1.003
hi 1.10
hi 1.22
hi 1.301
hi 1.410
hi 1.667
low 3.32

 PTO Port Overdrive/Doubler

Warn/Saturn

normal 1.00
od 0.75

ATV 30% OD

normal 1.00
od 0.70

Rover LT230 Roamerdrive

normal 1.00
od 0.72

BW1339 Low Range Adapted to D18

high 1.00
low 2.57
Calculations
Engine RPM
Transmission Ratio : 1
Ahead of Tcase Doubler/OD : 1
Overdrive Ratio : 1
Transfer Case Ratio : 1
Ring & Pinion Ratio : 1
Tire Diameter inches
 
Total Gear Ratio : 1
Speed MPH

Discussion

The speed at which a vehicle travels can be calculated from the engine speed, the gear ratios, and tire size.

engine rpm * tire circumference in inches * 60 minutes/hour
transmision gear * mid doubler/OD gear * tranfercase gear * PTO OD gear * axle gear * 63360 inches/mile

The total gear ratio is a combination of the transmission, overdrive, transfer case and the axle ratios. Engine RPM divided by total gear ratio, multiplied by the tire diameter and converted for units of measurement, gives vehicle's speed of travel.

This calculator was originally created by Richard B. Grover and the original version is hosted here: https://www.public.asu.edu/~grover/willys/speed.html