Ford Bronco Speedo Gearing

 

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Ford Bronco Speedo Gearing

 

 


To adjust for changing tire size:

 

http://home.att.net/~jroal/drive.htm

 

Ford Speedometer Driven Gear Calculator

Enter the input values below and click compute. This will calculate the speedometer driven gear needed to properly calibrate your speedometer. Always recheck the speedometer calibration!  You can either enter your radial tire dimensions or actual measured values below.  Select which one you want used for calculations with these radio buttons:
Use Measured Diameter (best)Use Radial Designation     



Inputs

Measured Dimensions

 

Radial Dimensions

Gear Ratio

:1

Radial Size: mm

Tire Diameter

Inches 

Profile: 

Speedo Drive Gear

Teeth

Rim Size: Inches

PSOM Exciter Ring Teeth

Teeth 

Note: Programmable Speedometer/Odometer Modules (PSOM) are used on most 1992 through 1998 Ford trucks, Vans, and RV's only.  Ignore this entry, and the PSOM constant below, for other vehicles.


Results

Revolutions/mile

Rev/mile

Driven gear needed

Teeth

PSOM constant

Radial Diameter: 

Inches

 

 

http://www3.telus.net/cbradley/speedogearchange.html

Old tire x Old Gear / New Tire = New Gear
OT x OG / NT = NG

 

Note - Rumor has it that 31" tires usually had a 19 tooth gear, and 235/75/15 tires had a  21 tooth gear

Example:

Old Tire - 29"
Old Gear - 19 tooth
New Tire - 33"
New Gear - ?

 

235/75/15 = 28.9"

 

If you change tire size and gears (or just gears), you have to go one step further:

New Gear / Old Ratio x New Ratio = New Gear

 

Old Tire

Old Gear


New Tire

New Gear

Old Ratio

 

New Ratio

 

New Gear

 

28.9

x 19

= 549.1

/ 33

= 16.639 (17 tooth)

 / 3.55

x 4.56

21.8

29

x 19

= 551

/ 33

= 16.697 (17 tooth)

/ 3.55

x 4.56

21.8

31

x 19

= 589

/ 33

= 17.848 (18 tooth)

/ 3.55

x 4.56

23.1

28.9

x 19

= 549.1

/ 36

= 15.253 (15 tooth)

/ 3.55

x 4.56

19.59

 

 

 

 

 

 

 

 

 

Each tooth on the speedo gear adjusts your speedometer reading by approx. 5%. So when you add a tooth, you reduce the speedometer reading by 5%.
 

 

If you figure in the old speedo gear size with the new tire size and then adjust for the gear change size by 113%.

 

    19 tooth x 1.13 = 21.47

Rear Gear Ratio

Factory Axle Code

2:73:1 Ratio

8M

3.08:1 Ratio

YZ

3.27:1 Ratio

5E

3.55:1 Ratio

2K

3.73:1 Ratio

6W

4.10:1 Ratio

N/A

 

Internal Drive Gears

Part Number

Description

E3ZZ-17285-B

6 Tooth Internal Drive Gear / Black

E3ZZ-17285-A

7 Tooth Internal Drive Gear / Yellow

F0ZZ-17285-A

8 Tooth Internal Drive Gear / Green


Note: The 6 tooth will offer the most combos for numerically higher gear ratios and the greatest degree of accuracy.

Manual Transmissions with 6 Tooth Drive Gear

  • Not found in OEM applications

Part Number

Description

N/A

3.08 Gear Ratio / Not possible

C0DZ-17271-A

3.27 Gear Ratio / Maroon 16 Speedo Gear

C3DZ-17271-C

3.55 Gear Ratio / White 17 Speedo Gear

C0DD-17271-B

3.73 Gear Ratio / Yellow 18 Speedo Gear

C1DZ-17271-A

4.10 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A

4.30 Gear Ratio / Red 21 Speedo Gear

Manual Transmissions with 7 Tooth Drive Gear

  • 1983-1989 T-5 OEM

  • Pre 1993 T-5 Aftermarket

  • 1996-1998 Cobra T-45 OEM

  • All Tremec Transmissions

Part Number

Description

C0DZ-17271-A

2.73 Gear Ratio / Maroon 16 Speedo Gear

C0DD-17271-B

3.08 Gear Ratio / Yellow 18 Speedo Gear

C0DZ-17271-B

3.27 Gear Ratio / Pink 19 Speedo Gear

C1DZ-17271-A

3.55 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A

3.73 Gear Ratio / Red 21 Speedo Gear

Jeep Part #j3167393

4.10 Gear Ratio / White 23 Speedo Gear

Manual Transmissions with 8 Tooth Drive Gear

  • 1990-1995 T-5 OEM

  • 1996-1998 T-45 OEM Except Cobra

Part Number

Description

C0DD-17271-B

2.73 Gear Ratio / Yellow 18 Speedo Gear

C1DZ-17271-A

3.08 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A

3.27 Gear Ratio / Red 21 Speedo Gear

Jeep Part #j3167393

3.55 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393

3.73 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393

4.10 Gear Ratio / White 23 Speedo Gear

Automatic Transmissions with 7 Tooth Drive Gear

  • 1983-1989 Automatic Transmissions

Part Number

Description

D0AZ-17271-A

2.73 Gear Ratio / Blue 16 Speedo Gear

C7AZ-17271-B

3.08 Gear Ratio / Gray 18 Speedo Gear

C7VY-17271-A

3.27 Gear Ratio / Tan 19 Speedo Gear

C8SZ-17271-B

3.55 Gear Ratio / Orange 20 Speedo Gear

D0OZ-17271-B

3.73 Gear Ratio / Purple 21 Speedo Gear

Jeep Part #j3167393

4.10 Gear Ratio / White 23 Speedo Gear

Automatic Transmissions with 8 Tooth Drive Gear

  • 1990-1998 Automatic Transmissions

Part Number

Description

C7AZ-17271-B

2.73 Gear Ratio / Gray 18 Speedo Gear

C8SZ-17271-B

3.08 Gear Ratio / Orange 20 Speedo Gear

D0OZ-17271-B

3.27 Gear Ratio / Purple 21 Speedo Gear

Jeep Part #j3167393

3.55 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393

3.73 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393

4.10 Gear Ratio / White 23 Speedo Gear

 

 


 

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