Gear Ratio & MPH

Speedometer Gear

If your speedometer reads too low, use a speedometer drive gear with fewer teeth. If your speedometer reads high, you need a drive gear with more teeth. Do this in one-tooth increments. A drive gear with 18 teeth is going to turn faster (and read faster) than a drive gear with 21 teeth. If your speedometer is reading 10 mph too high and you have an 18-tooth drive gear, you need a 20-tooth drive gear. The highest number of teeth available on a Ford speedometer drive gear is 21. After that, you must run a reducer that was common to Fords with 3.89:1, 3.91:1, 4.11:1, and 4.30:1 rearend gears. Taller tires will make the speedometer read lower. Shorter tires will make it read higher. Even tire inflation can affect speedometer reading.

Here is a good link:  http://429mustangcougarinfo.50megs.com/speedo_gears.htm
 


 Manual Transmission

16-teeth-wine(C0DZ-A) 17-teeth-white(C3DZ-C) 18-teeth-yellow(C0DD-B) 19-teeth-pink(C0DZ-B) 20-teeth-black(C1DZ-A) 21-teeth-red(C4OZ-A)

Automatic Transmission

16-teeth-blue(D0AZ-A) 17-teeth-green(C7SZ-A) 18-teeth-gray(C7SZ-B) 19-teeth-tan(C7VY-A) 20-teeth-orangeC8SZ-B) 21-teeth-purple(D0OZ-B)

Calculator

 
  Miles Per Hour
  Tire Diameter In Inches
  Final Axle Ratio
  Final Transmission Gear Ratio

R.P.M. 

 

 

 

RPM=
 

 MMPH X Trans Ratio (in high gear) X Rear End Ratio X 336
                                 Tire Heighteight
 
13 INCH
TIRES 		TIRE
HEIGHT
175 50 13 19.89
215 50 13 21.46
  
175 60 13 21.27
185 60 13 21.74
195 60 13 22.21
205 60 13 22.69
  
165 65 13 21.44
  
165 70 13 22.09
175 70 13 22.65
185 70 13 23.2
195 70 13 23.75
  
155 80 13 22.76
165 80 13 23.39
175 80 13 24.02
185 80 13 24.65

 

 

 

 

 

 

 

 

 

 

 

 

 
14 INCH
TIRES 		TIRE
HEIGHT
205 50 14 22.07
245 50 14 23.65
265 50 14 24.43
  
185 55 14 22.01
195 55 14 22.44
205 55 14 22.88
  
185 60 14 22.74
195 60 14 23.21
205 60 14 23.69
215 60 14 24.16
225 60 14 24.63
235 60 14 25.10
245 60 14 25.57
  
165 65 14 22.44
175 65 14 22.96
185 65 14 23.47
195 65 14 23.98
  
175 70 14 23.65
185 70 14 24.20
195 70 14 24.75
205 70 14 25.30
215 70 14 25.85
225 70 14 26.40
  
185 75 14 24.93
195 75 14 25.52
205 75 14 26.11
215 75 14 26.70

 

 

 

 

 

 

 
15 INCH
TIRES 		TIRE
HEIGHT
195 45 15 21.91
  
195 50 15 22.68
205 50 15 23.07
225 50 15 23.86
245 50 15 24.65
265 50 15 25.43
275 50 15 25.83
295 50 15 26.61
305 50 15 27.01
  
185 55 15 23.01
195 55 15 23.44
205 55 15 23.88
225 55 15 24.74
  
185 60 15 23.74
195 60 15 24.21
205 60 15 24.69
215 60 15 25.16
225 60 15 25.63
235 60 15 26.10
245 60 15 26.57
255 60 15 27.05
275 60 15 27.99
315 60 15 29.88
  
185 65 15 24.47
195 65 15 24.98
205 65 15 25.49
215 65 15 26.00
  
205 70 15 26.30
215 70 15 26.85
225 70 15 24.70
235 70 15 27.95
255 70 15 29.06
  
195 75 15 26.52
205 75 15 27.11
215 75 15 27.70
225 75 15 28.29
235 75 15 28.88
265 75 15 30.65

 

 

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