Wheel Drive Speed Sensor

  1. Mark the tire on which the speed sensor is installed using chalk or a piece of tape as shown below.

  2. Mark the corresponding spot on the ground.

  3. Count 10 full revolutions of the wheel while traveling in a straight path. The mark must stop with the chalk or tape in the same orientation that it began at the starting point.

  4. Calculating the Speed Cal with a Wheel Magnet Speed Sensor System

  5. Mark the stopping point and measure the distance between the starting and stopping marks on the ground in inches [dm]. Round to the nearest whole number.

    Note:  This measurement is critical to the performance of the ROS device. Measure Carefully. Be sure tire is properly inflated before measuring. If possible, measurements should be made in the type of soil in which the vehicle will be operating. Tire circumference will vary when measured in soft or hard packed soil. For best results, measure several times and average the results.

  6. Enter this measurement as the adjusted speed cal.

Typically, four magnets are used with the wheel drive speed sensor. However, to ensure accurate speed readings for large tires and very low speed applications, additional wheel magnets may be necessary. Any even number of magnets may be used as long as they are of alternating color and equally spaced. After calculating the speed cal, this number must be adjusted according to the number of magnets installed using the following formula:
where ADJ = Adjusted Speed Cal, NM = Number of Magnets used and D = the Distance Measured.

Note:  For Example, the distance measured between starting and stopping marks is 1200 and six magnets are installed.


The Adjusted Speed Cal is 800.

Last Revised: Jul 2024