Speedo Gear Change Calculator

Got or want a new tire size on your vehicle and curious to know how much your speedometer has been affected? Want to get new gears and worried about the change to the speedometer? This calculator is here to help you determine the overall accuracy of your speedometer based on differential, tire size changes or both.

Have your wheels changed size?

What is the original tire size?

/ R

What is the new tire size?

/ R

Have your differential gears been changed?

ex: 4.10

Original Gear Ratio


New Gear Ratio


Where is your speedometer sensor located?

History of the Speedo Gear Change Calculator

I originally designed the Speedo Gear Chang Calculator because I had bought oversized wheels for my truck. The tires caused my speedometer to offset by almost 18%. I wanted to get the right gears for my rear axle to accommodate the size change. I couldn’t find a calculator that would calculate both the tire change and a gear change together, so I built one. I figured that others could use this hand tool as well. Which not too surprisingly, this tool generates a fair bit of traffic to this website.