Speedometer Calibration

You may need to recalibrate your speedometer if you have swapped transmissions or differentials, or if you have changed your tire size. Calibration is performed by changing either or both of the speedometer drive gears (normally located at the rear of the transmission). The following Excel spreadsheet will calculate your new drive ratio:  Speedometer Calibration.   The table below is only a representation of the excel interface. 

Hope this makes your life a little easier :)

Speedometer Calibration
Tire section (mm) 195.00
Aspect ratio 70.00
Rim size (in) 14.00
Rear gear ratio 3.54
Speedo revs @ 60 mph 1024.00 <<<<Most foreign cars are 1024, while American are 1000
Tire diameter 24.75
Distance per tire revolution (in) 77.75
Tire revs per mile 814.94
Tire revs per 60 miles 48896.29
Tire rpms @ 60 mph 814.94
Driveshaft rpms @ 60 mph 2884.88
Req'd speedo drive ratio 2.82 <<<<Number of teeth on pencil gear divided by number of teeth on output shaft
 

Questions or Comments?  E-mail me at:  [email protected] .

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This page was last edited on 12/28/01.

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