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Or lower if you have gone with a smaller tire than stock. Our speedometer calibration calculator will get you the answer you are looking for. Enter your original tire size, your new tire size, and then play with the miles per hour to see how much faster you are going at different speeds.


A tire with a diameter of 30 inches will cover more ground -- about 94.2 inches. Calibration adjusts for these variances and is done by the manufacturer, which sets up the speedometer gear to correspond with the factory-installed ring and pinion ratio and tire size. A car owner may have to recalibrate his speedometer if he makes changes that ...


The faster the gears spin, the more electromagnetic field is created and the further the needle goes up on the speedometer in the dashboard. Therefore, as long as the wheels and tires are stock sized, the speedometer will read accurately. Let's look at why changing tire size would affect the speedometer.


Tire Size and Speedometer Accuracy . If you are planning on, or have already replaced your original equipment tires with a different tire size, it is important to remember that changing your tire size can affect the accuracy of your speedometer.


Bigger tires will cause your speedometer to register a speed that is slower than your actual speed. For example, if your speedometer says 35 miles per hour on 20-inch diameter tires, changing to 23-inch diameter tires will make your true speed 40.25 mph, even though your speedometer will still show 35 mph.


How a Change in Tire Size Affects Speedometer Accuracy When you change out your tires and wheels for a larger wheel, you always want to respect the overall diameter (OD) of the original tire. A lower profile tire must be placed on a larger wheel to keep the OD close to the same as the tire/wheel combination being replaced.


Speedometer ratio adjustment calculator. Ever wonder how far off your speedometer is with your new bigger tires? I'm using a simple ratio calculation, so this info will only approximate your corrected speed and depends on the accuracy of tire size diameters (assumimg nothing but tire size has changed).


How to Fix Your Speedometer for Different Size Tires. Have you changed your tire size or final-drive gear? You just made your speedo and odometer inaccurate.


To find out speedometer error, in the calculator below select the original tyre size, the new tyre size, enter kilometers or miles per hour into the "Enter Speedometer Reading" section and then click on the "Calculate Actual Speed" button to see how much faster or slower your car actually is going at different speed readings on your speedometer .


Tire Change / Speedometer Change Calculator July 12, 2016 Roadkill Customs Technical Info This calculator is designed to give information related to tire size changes and the general impact they have on the calibration of a speedometer.