When it comes to changing the size of your tire or rear axle ratio in your vehicle, this alteration will render your speedometer inaccurate. You will need a mechanical adaptor for all cable design or the electronic ratio adaptor or ERA for an electronic design. We have explained in detail about these below.
- Mechanical radio adaptor
In almost every vehicle, the speedometer adaptor calibration is based on a specific tire and the transmission ratio. These very factors were considered by the speedometer manufacturer to build a proper combination of gears and worms present inside the head of the speedometer to gather correct speed readings. Many car manufacturers and people getting their cars customized use various tires and/or transmission ratios instead of the equipped OEM. In this case, the ratio should be mandatorily established. Generally, if the transmissions or tires, entailing the car differential has been or will be changed by you, or if any other kind of alterations are made that aren’t deemed original or factory approved ones, the ratio needs to be mandatorily adjusted. And this job is best done by a professional.
How to test ratio: you need to stop a mile marker. Record the odometer rating which includes the 10th as well. Drive 10 miles again and stop at the mile marker. Record the reading, including the 10th again. Subtract the first reading from the second. This is the cable delivery ratio which is incorrect or correct. If the latter, then the answer will obviously be 10.0. If not, then the transmission error and the ratio must be corrected.
- Electronic radio adaptor
The automotive industry comes bearing a variety of part sizes, shapes, types, and descriptions, no matter what make, model or year, however a few things being standard. And one of them is the number of revolutions a speedometer cable makes for each mile you have travelled. These days, electronic pulses are now replacing the rotating cable but the principle is same nonetheless. The Pulse Ratio means the number of pulses per mile travelled always stays the same, no matter the speed, since the distance travelled is also the same and the pulses occurred each mile are same as well, no matter the speed. But this Pulse Ratio can be varied when the changes are made, which can also change the number of electronic pulses per mile on a specific vehicle. This is most commonly occurred because of the changing tire size.
However, other alterations could result the same too. Whenever the Pulse ratio is thrown off, the odometer or the speedometer will be incorrect and the rectifications should be made. This relative distinction between the true speed and the speed shown on the speedometer is referred to as the Variance Ratio. It can be rectified with the help of an Electronic Radio Adapter. It can be installed easily. You just have to input, output, hot, and ground. Set the dip switches by paying heed to the Calibration table on the installation instructions mention on the ERA and you are all set.