Each individual who owns a vehicle must get his or her speedometer calibrated periodically. This should be done to ensure that the torque created by the magnetic field appropriately matches the actual speed of the car. This calibration must keep several factors in mind, such as the proportions of the gears in the drive cable, the final drive proportion in the differential, and the tires’ diameter. Each of these factors plays a role in the overall speed of a vehicle.

Think about tire size, for one. When the axle of a wheel completes one full spin, the tire that it is attached to is able to make one revolution. The thing is, if a vehicle is equipped with larger tires—that have a large diameter—it will travel a greater distance than a car equipped with smaller diameter tires. This is because the distance covered by a tire in one revolution is equal to its circumference. A tire with a 20 inch diameter will travel 62.8 inches of ground in one revolution, while a 30 inch diameter tire will cover approximately 94.2 inches, which is clearly more ground.

Paying the speedometer calibration cost will adjust for these variances. The speedometer gear is set up to correspond with the factory installed ring and pinion proportion, as well as tire size. The owner of a vehicle may have to get his speedometer recalibrated if he makes changes that will no longer qualify the vehicle as factory specifications.

If you do not want to pay the speedometer calibration cost at the dealer, you can try to do the reset from home. Recalibration can be accomplished by tinkering with the hairspring, the permanent magnet, or both. The strength of the magnetic field is typically the simplest component to change. However, it requires a strong electromagnet that can be used to adjust the permanent magnet’s strength in the speedometer. This has to be done until the needle balances the input from the rotating drive cable.

Of course, there is another option besides attempting recalibration from home or paying the expensive calibration cost at the dealer. The smart thing to do would be to send the unit in to the company Safety Restore. Safety Restore provides quality and affordable speedometer calibration services.