GM Speedometer Calibration

Standard V8 Rear-Wheel-Drive Applications (1999–Present)

1. Open VCM Editor and go to Edit > Gear/Tire Wizard.
2. Enter your new tire size and/or gear ratioin the columns on the right.
   • If the tire size or gear ratio hasn’t changed, enter the current values.
3. Click Adjust to calculate new values, including:
   • VSS Pulses/Mile
   • Trans Revs/Mile
   • Final Drive Ratio
   • Tire Revs/Distance
4. When satisfied with the adjustments, click Save Changes in the top-right.

V8 Rear-Wheel-Drive with Transaxle (Corvette) & V6 Front-Wheel-Drive (W-Body)

1. Enter your new tire size and/or gear ratio in the Gear/Tire Wizard.
2. Click Calculate for New Values to determine updated VSS Pulses/Mile and Trans Revs/Mile.
3. Click Save Changes once the settings are correct.

V6 Rear-Wheel-Drive Applications

1. Enter the new tire height (in inches) divided by the gear ratio.
2. Click Calculate for New Valuesto update:
   • VSS Pulses/Mile
   • Trans Revs/Mile
3. Click Save Changes once complete.

Transaxle & Front-Wheel-Drive Vehicles

• If the vehicle has a transaxle (e.g., Corvette) or is front-wheel-drive (e.g., W-Body), select Yes in the wizard.
• This setting is usually auto-selected but may need to be manually adjusted.

Axle Settings

• Tire Size: Enter the tire height in inches (even if metric units are selected).
• Gear Ratio: Enter the final drive ratio (e.g., 2.73, 3.08, 3.23, 3.42, 3.73, 4.10).

Speedometer Scalars

**Manual adjustments to these values are not recommended.**

• VSS Pulses/Mile: Number of pulses from the VSS sensor per mile traveled.
• VSS Pulses/Rev: Pulses per output shaft revolution (often equal to the number of teeth on the VSS sensor).
• VSS Pulses/Rev - Trans: Pulses per output shaft revolution (used for transmission output RPM calculations).
• Trans Revs/Mile: Output shaft revolutions per mile, used for shift and TCC calculations.
• Drive Sprocket Ratio: Ratio from the engine to transmission (e.g., Pontiac GTP V6 Final Drive = 3.29 / 1.121 = 2.93).
• VSS Tire Revs/Dist: Tire revolutions per mile/kilometer.
• VSS Tire Revs/Dist - Err: Value used when a VSS error is detected.
• Final Drive Ratio: The differential gear ratio.
• Final Drive Ratio - VSS Error: Used when a VSS error is detected.

Auto Scale Transmission Tables

• This option automatically scales the transmission shift points to match the new gear ratio and tire size.
• A manual scaling option allows users to enter a custom scaling factor for fine-tuning shift RPMs.