Why is my speedometer off after changing tire size?

If your speedometer seems to be reading higher or lower than your actual speed after installing new tires, you are not alone. This is a very common issue when switching to a different tire size and there is a straightforward explanation for why it happens. Here is everything you need to know.

Why does this happen?

Your speedometer is calibrated by your vehicle's manufacturer based on the size of your factory tires. Here is how it works:

• Your speedometer calculates your speed based on how many times your tires rotate per mile
• A larger tire has a bigger circumference than a factory tire, which means it covers more ground with each rotation and rotates fewer times per mile
• A smaller tire has a smaller circumference and rotates more times per mile
• When you install tires that are a different size than your factory tires, the number of rotations per mile changes, which causes your speedometer to read inaccurately
• The bigger the difference between your new tire size and your factory tire size, the more noticeable the speedometer discrepancy will be

Will my speedometer read high or low?

The direction of the inaccuracy depends on whether your new tires are larger or smaller than your factory tires. Here is what to expect:

• If your new tires are larger than your factory tires, your speedometer will read lower than your actual speed. This means you may be traveling faster than your speedometer indicates
• If your new tires are smaller than your factory tires, your speedometer will read higher than your actual speed. This means you may be traveling slower than your speedometer indicates

Does this affect anything else on my vehicle?

Yes, a change in tire size can affect more than just your speedometer. Here is what else may be impacted:

• Odometer accuracy: Your odometer calculates mileage based on the same tire rotation data as your speedometer. If your speedometer is off, your odometer may also be recording mileage inaccurately
• Transmission shift points: Some vehicles use wheel speed data to determine when to shift gears. An inaccurate reading from a larger or smaller tire can affect how and when your transmission shifts
• ABS and traction control: Your vehicle's ABS and traction control systems rely on wheel speed sensors that can be affected by a change in tire size. In some cases this can trigger warning lights on your dashboard
• Fuel economy estimates: If your vehicle displays a fuel economy estimate, this calculation may also be affected by the change in tire size

How do I fix my speedometer?

The good news is that a speedometer that is off due to a tire size change is a correctable issue. Here are the most common solutions:

• Tuner or programmer: A handheld tuner or programmer can recalibrate your speedometer to account for your new tire size. This is one of the most common and affordable solutions and is available for most popular truck and SUV platforms. Many local shops or performance tuners can handle this for you
• Dealership or shop recalibration: Many dealerships and local repair shops can recalibrate your speedometer to match your new tire size using diagnostic software. This is a quick and straightforward process for most vehicles
• PCM or ECU recalibration: For some vehicles, a more in depth recalibration of the powertrain control module or engine control unit may be needed to fully correct the speedometer and other affected systems

Is it safe to drive with an inaccurate speedometer?

While a slightly off speedometer is not an immediate safety emergency, it is important to be aware of the inaccuracy while driving. Here is what to keep in mind:

• If your speedometer reads lower than your actual speed, you may unknowingly be exceeding the speed limit
• It is always a good idea to get your speedometer recalibrated as soon as possible after installing a significantly different tire size
• Until your speedometer is recalibrated, be mindful of the inaccuracy and use extra caution when monitoring your speed

How do I know how much my speedometer is off?

There are a few ways to get a rough idea of how much your speedometer has changed with your new tire size:

• Online tire size calculators are available that compare your old and new tire sizes and calculate the approximate speedometer error. Simply enter your old and new tire sizes to get an estimate
• Using a GPS device or navigation app that displays your actual speed is another easy way to compare against your speedometer reading

Not sure what tire size is right for your vehicle?

Using our guided fitment tool on our homepage is the best way to find tire sizes that work well with your specific vehicle. You can also reach out to our sales team and we will be happy to help you find a setup that minimizes the impact on your speedometer and other vehicle systems!