Electronic Ratio Adapter (ERA)

Now You Have the Solution to Your Speedometer Inaccuracy Problems...

Any change in a vehicle's tire size or rear axle ratio will cause the speedometer reading to be inaccurate. The Electronic Ratio Adapter (ERA) is designed to correct this problem. With the ERA, you simply hook up four wires, set the DIP switches according to the calibration table included with your order, and you are ready to go.

What does the Electronic Ratio Adapter do?

The automotive industry has a great variety of part sizes, types, shapes and descriptions, but regardless of make, model or year, a few things are standard. One of those standards has been the number of revolutions a speedometer cable will make for each mile traveled.  Nowadays, electronic pulses have replaced the rotating cable, but the same principle applies. The Pulse Ratio (the number of pulses per mile traveled) remains the same, regardless of speed, since the same distance is traveled and the same number of pulses have occurred each mile no matter what the speed was during that mile.

However, this Pulse Ratio can be made to vary from the true when modifications are made which change the number of electronic pulses per mile on a particular vehicle. This is most commonly caused by changing the tire size (increasing the outside diameter of the tires will cause the tire to travel further before making a complete revolution), but other modifications could have the same result. When the Pulse Ratio is thrown off, the speedometer/odometer will be inaccurate and corrections must be made.

This relative difference between true speed and the speed indicated on the speedometer is called the Variance Ratio, and it is corrected using the Abbott Electronic Ratio Adapter (ERA).

The first step is to Calculate the Variance Ratio precisely.  There are several ways to calculate this ratio on a particular modified vehicle.

One way is to run the modified vehicle exactly ten miles as measured by highway mile markers and note the speedometer's mileage (odometer) reading at the course's start and finish.  Subtract starting odometer reading from the ending odometer reading to determine indicated mileage over the ten mile course.  Divide the actual distance traveled by the odometer's indicated mileage to get the Variance Ratio.        Example:10 divided by ?? equals Ratio.

Another way is by comparing your vehicles speedometer indicated speed, to a dynamometer, radar, or by driving along side of someone (if their speedometer is accurate).   Divide the actual speed by your shown speed  to get the Variance Ratio.     Example:  Actual divided by shown equals Ratio.

Figure your Variance Ratio and Calculate your new settings.
Calculations Page

The next step is to look up this Variance Ratio in the "ratio" column of the "Abbott Electronic Ratio Adapter Calibration Table" and set your dip switches accordingly.  The signal from the speed sensor is inputted into the Abbott Electronic Ratio Adapter, modified to compensate for the Variance Ratio, and outputted as the correct signal to your ECM/Speedometer.

Wiring Diagram of Abbott Electronic Ratio Adapter:  

Cable-X         ERA         Calculations/Conversions         Variance Ratio (Calibration) Chart

Visit our homepages:

Abbott Enterprises at Atrol.com

Abbott Enterprises at Abbott-tach.com

Need More Information? Send email here...

Abbott Enterprises, Inc.    901 West 4th Ave.       Pine Bluff, AR.  71601  USA  
(870) 535-4973  Fax: (870) 535-4970