How Tire Size Affects Speedometer Accuracy
Learn how changing tire size can affect speedometer accuracy, vehicle performance, and handling. Understand tire diameter and choose the right fitment today!
How Tire Size AffectsSpeedometer Accuracy
Your vehicle’s speedometer calculates speed based on how quickly the wheels and tires rotate. When you change the overall diameter of your tires, you change how far the vehicle travels with each rotation. As a result, installing a significantly larger or smaller tire can affect speedometer accuracy.
This is an important consideration when upgrading wheels and tires. At Automotive Expressions, we help drivers explore wheel and tire options while considering fitment, performance, and the effects of changing tire size.
How Does a Speedometer Measure Speed?
Your vehicle’s speedometer uses information from wheel speed sensors or other systems to estimate how fast you’re traveling. The system is calibrated based on the factory tire size and overall diameter.
When you change the tire diameter, the distance traveled during each rotation also changes. This can cause the speedometer reading to differ from your actual speed.
What Happens With Larger Tires?
When you install a taller tire with a larger overall diameter, it travels farther with each rotation. Because the tire rotates fewer times over the same distance, the speedometer may show a lower speed than your actual speed.
For example, if your speedometer shows 60 mph, your actual speed could be higher depending on the difference between your new and original tire sizes.
What Happens With Smaller Tires?
Smaller tires travel a shorter distance with each rotation and must rotate more times to cover the same distance. As a result, the speedometer may show a higher speed than you’re actually traveling.
The larger the difference between your original tire and new tire diameter, the greater the potential impact on accuracy.
How Much Does Tire Size Affect Speedometer Accuracy?
The effect depends on how much the overall diameter changes.
For example, if a vehicle originally has a 28-inch tire and you install a 30-inch tire, the speedometer could show 60 mph while your actual speed is approximately 63.3 mph. This is a simplified example, and actual results vary by vehicle.
A road test can help you compare your vehicle’s speedometer reading with a GPS-based speed reading. You can also compare your speedometer to mile markers over a known distance, although this method is generally less precise.
Why Overall Tire Diameter Matters
When comparing tire sizes, overall diameter is more important than simply looking at tire width or wheel diameter.
When upgrading from a smaller wheel to a larger wheel, you can often use a lower-profile tire to maintain a similar overall diameter. This is commonly known as plus sizing.
Maintaining a similar overall diameter can help minimize changes to speedometer accuracy while allowing you to achieve the larger-wheel appearance you want.
Can Changing Tire Size Affect Other Systems?
Yes. A significant change in tire diameter can potentially affect systems that rely on wheel speed information, including:
- Anti-lock brakes
- Traction control
- Electronic stability control
- Some driver-assistance features
- Certain transmission functions
The impact varies by vehicle, so it’s important to consider your manufacturer’s specifications before making a significant tire size change.
Can You Recalibrate a Speedometer?
Depending on your vehicle, it may be possible to recalibrate the speedometer or adjust electronic systems after changing tire size. Options vary by make, model, and year.
If you’re considering a significant change, consult an automotive professional to determine whether recalibration is necessary or available.
How to Minimize Speedometer Changes
If you want to change your tire size while minimizing the effect on speedometer accuracy, choose a tire with an overall diameter close to the factory size.
When upgrading wheels, a lower-profile tire can compensate for a larger wheel diameter. Before installing a new tire size, compare:
- Original tire diameter
- New overall diameter
- Tire width
- Aspect ratio
- Wheel diameter
- Load rating
- Speed rating
- Vehicle clearance
A tire size calculator can help compare dimensions, but proper fitment involves more than diameter alone.
Get Help Choosing the Right Tire Size
Changing tire size can be an excellent way to customize your vehicle, but it can also affect speedometer accuracy, handling, performance, and other vehicle systems.
At Automotive Expressions, we help drivers evaluate wheel and tire combinations based on their vehicles and goals. Whether you’re upgrading to larger wheels, installing a taller tire on a truck, or creating a custom setup for your car or SUV, our team can help you understand your options.
Contact Automotive Expressions to explore your wheel and tire upgrade options and find a setup designed to fit your vehicle.
Frequently Asked Questions About Tire Size and Speedometers
Do larger tires make my speedometer read incorrectly?
They can. A larger overall diameter may cause the speedometer to display a lower speed than your actual speed.
Do smaller tires affect speedometer accuracy?
Yes. Smaller tires may cause the speedometer to display a higher speed than you’re actually traveling.
Does tire width affect my speedometer?
Tire width alone generally has little effect. Overall diameter is the more important factor, although changing width may also change other tire dimensions.
How can I minimize speedometer changes when upgrading wheels?
Choose a tire size with an overall diameter close to the original tire size. When moving to larger wheels, a lower-profile tire can help maintain a similar overall diameter.
Can Automotive Expressions help me choose the right tire size?
Yes. Automotive Expressions can help you evaluate tire and wheel combinations based on your vehicle, desired appearance, and fitment needs, including considerations related to speedometer accuracy.