Knowledgebase
Knowledgebase: Support
GM Speedometer Calibration

Standard V8 Rear Wheel Drive Applications (1999 to Current)

  1. Using Gear/Tire wizard in VCM Editor (Edit> Gear/Tire Wizard) Insert your new tire and gear in the columns on the right. If your tire height has not changed, enter the same value. If your gear has not changed enter the same gear value.
  2. When you have entered the correct values for your vehicle click the "Adjust" button. This will use the values you entered to determine the new VSS Pulses/Mile, Trans Revs/Mile, Final Drive ratio, Tire revs/dist values found below.
  3. When you are satisfied with your changes, click the Save Changes button on the top right of the form.


V8 Rear Wheel Drive Applications With Transaxle (Corvettes) and V6 Front Wheel Drive Applications (W Body)

  1. Insert your new tire and gear in the columns on the right. If your tire height has not changed, enter the same value. If your gear has not changed enter the same gear value.
  2. When you have entered the correct values for your vehicle click the "Calculate for New Values" button. This will use the values you entered to determine the new VSS Pulses/Mile and Trans Revs/Mile found below.
  3. When you are satisfied with your changes, click the Save Changes button on the top right of the form.


V6 Rear Wheel Drive Applications (All)

  1. To make changes enter in your new tire height (in inches) divided by your new gear ratio.
  2. When you have entered the correct values for your vehicle click the "Calculate for New Values" button. This will use the values you entered to determine the new VSS Pulses/Mile and Trans Revs/Mile found below.
  3. When you are satisfied with your changes, click the Save Changes button on the top right of the form.


Transaxle or Front Wheel Drive:
      If your vehicle has a transaxle like the corvettes, or is front wheel drive like W Bodies, select yes. In most cases this will be auto-selected for you but in some cases you may need to select it manually.


Axle Settings

  • Tire Size: Tire Height measured in inches (NOTE: this is in inches regardless if metric units selected)
  • Gear Ratio: Gear Ratio (eg: 2.73, 3.08, 3.23, 3.42, 3.73, 4.10, ...)


Speedometer Scalars (We do not recommend that you manually adjust these values)

  • VSS Pulses/Mile: This value is used to calculate the speed value for the engine routines and gauge cluster. It is the number of pulses received from the VSS sensor per mile traveled. If you know your gear, tire and location of your VSS sensor you can calculate this value manually.
  • VSS Pulses/Rev: This is the number of pulses received from the VSS sensor per output shaft revolution (used to calculate trans output RPM). It is usually equal to the number of teeth on the VSS sensor (depending on the sensor location).
  • VSS Pulses/Rev - Trans: This is the number of pulses received from the VSS sensor per output shaft revolution (used to calculate trans output RPM). It is usually equal to the number of teeth on the VSS sensor (depending on the sensor location).
  • Trans Revs/Mile: The number of trans output shaft revolutions per mile. This value is used to calculate the speed that is used for shift and TCC calculations. (A tire sanity check value is provided alongside so you can check the trans tire size calibration against the speedo tire size calibration. This is also useful for troubleshooting accurate speedo but trans shifting strangely issues).
  • Drive Sprocket Ratio: This is the drive chain/sprocket ratio from the engine to the trans. (eg. for a Pontiac GTP V6 the final drive ratio is 2.93. This is calculated from a diff ratio of 3.29 divided by the drive sprocket ratio of 1.121).
  • VSS Tire Revs/Dist: The number of tire revolutions per mile or kilometer.
  • VSS Tire Revs/Dist - Err: The number of tire revolutions per mile or kilometer. Used when a VSS Error is detected.
  • VSS Tire Revs/Dist - Trans: The number of tire revolutions per mile or kilometer.
  • VSS Tire Revs/Dist - Trans Error: The number of tire revolutions per mile or kilometer. Used when a VSS Error is detected.
  • Final Drive Ratio: The final drive (differential) gear ratio.
  • Final Drive Ratio - VSS Error: The final drive (differential) gear ratio, used when a VSS error is detected..
  • Final Drive Ratio - Trans: The final drive (differential) gear ratio.
  • Final Drive Ratio - Trans Error: The final drive (differential) gear ratio, used when a VSS error is detected..


Auto Scale Transmission tables

This option will automatically scale the transmission tables to adjust for a new gear or tire to maintain similar shift RPM's. There is also a manual scaling option where you can enter you own scaling factor to scale the trans tables up and down.

(0 vote(s))
Helpful
Not helpful