Why You Need a Speedometer Calibrator After Larger Tires or Gear Changes Larger tires are one of the most common upgrades on Toyota and Lexus off-road vehicles. They improve ground clearance, help off-road, and often make the vehicle look better. The downside is that your vehicle was calibrated for the factory tire size. Once the tire diameter changes, the speedometer and odometer may no longer be accurate. That is why we developed the Lutz Auto line of speedometer calibrator