Table 2

Engine Revolutions Per Tire Turn*

(Assumes 35” diameter tires)

 Four-Speed Transmission     

 

Rear Axle Ratio1

1st Gear

2nd Gear

2nd

OD

3rd Gear

3rd

OD

4th Gear

RPMs2

At

60 mph

4th

OD

RPMs2

At

60 mph

3.71 (14/52)

12.61

8.24

6.42

5.53

4.30

3.71

2,136

2.89

1,662

 

 

 

 

 

 

 

 

 

 

3.47 (15/52)

11.80

7.70

6.00

5.17

4.03

3.47

1,998

2.70

1,554

3.25 (16/52)

11.05

7.22

5.62

4.84

3.77

3.25

1,871

2.53

1,456

3.06 (17/52)

10.40

6.79

5.29

4.56

3.55

3.06

1,762

2.38

1,371

2.89 (18/52)

9.83

6.42

5.00

4.31

3.35

2.89

1,664

2.25

1,295

2.74 (19/52)

9.32

6.08

4.74

4.08

3.18

2.74

1,577

2.13

1,227

 

Three-Speed Transmission     

 

Rear Axle Ratio1

1st Gear

2nd Gear

2nd

OD

3rd Gear

RPMs2

At

60 mph

3rd

OD

RPMs2

At

60 mph

3.71 (14/52)

10.61

5.60

4.38

3.71

2,136

2.89

1,662

3.47 (15/52)

9.92

5.24

4.09

3.47

1,998

2.70

1,554

3.25 (16/52)

9.30

4.91

3.84

3.25

1,871

2.53

1,456

3.06 (17/52)

8.75

4.62

3.61

3.06

1,762

2.38

1,371

2.89 (18/52)

8.27

4.36

3.41

2.89

1,664

2.25

1,295

2.74 (19/52)

7.75

4.14

3.23

2.74

1,577

2.13

1,227

Table 2 shows the number of engine revolutions for each revolution of the rear tires.  For example, with a four speed transmission in first gear (3.71 rear axle ratio), the engine revolves 12.61 times for each revolution of the rear tires.  The fourth gear output (high gear) is directly proportional to engine RPMs times the rear axle ratio, or 3.71 in this example.  With the Gear Vendors overdrive engaged, engine revolutions drop to 2.89 per rear tire revolution, or approximately 22% less than top gear without overdrive.

 1Ring and pinion gears shown in parenthesis.

 2Approximate RPMs at 60 mph are shown for each rear axle ratio in top gear with and without overdrive.

 

Section 1 - Disconnecting Torque Tube
Section 2 - Removing the Front Section of the Torque Tube
Section 3 - The Mathematics of an Overdrive
Section 4 - Checking Universal Joint and Bearnings
Section 5 - Installing Overdrive in Drive Line
Section 6 - Overdrive Lubrication
Section 7 - Connecting Speedometer and Electric Controls
Section 8 - Hooking up the Electronic Control Box
Section 9 - Hooking up Speedometer and Calibrating Output
Section 10 - The Overdrive in Operation
Section 11 - Overdrive Service
Section 12 - Crusing in Overdrive
Endnotes - Endnote
Table 1 - Silver Ghost Rear Axle Gear Ratios Comparisons
Table 2 - Engine Revolutions per Tire Turn
Table 3 - Overdrive Speedometer Gears for the Silver Ghost