Moses Ludel’s 4WD Mechanix Magazine – How-to: Measuring Speedometer Error
This how-to provides two simple methods for checking the speedometer and odometer accuracy.
(If bandwidth permits, view this video in ‘full-screen’ mode and HD 1080P quality!)
The magazine’s Ram 3500 “makeover” and 4.56:1 ring-and-pinion gear change now make the Dodge Ram a better trailer puller. For tire clearance, we raised the truck, using a 4-inch Mopar suspension lift. Oversized BFG tires and aftermarket 18″ wheels round out the package. In the process, the 35″ diameter tires and 4.56:1 axle gearing altered the speedometer calibration. Now we need to calibrate the speedometer!
The DRBIII scan tool enables speedometer calibration on 1998-2006 Chrysler vehicles. For models with a tone ring ABS sensor, the calibration involves changing the tire revolutions per mile in the PCM. Before using this scan tool, you need to know the percentage of speedometer error! (See the HD video for details.)