The odometer is undoubtedly one of the most important instruments on your car’s instrument cluster. However, how the odometer works can depend entirely on your vehicle because the way an odometer works is dependent on the size of your car’s tires.
That’s why different odometers are calibrated differently from one another. So in that regard, do bigger tires affect how the odometer works?
Bigger tires affect the odometer as larger tires naturally travel greater distances with every revolution made by the tire. However, that is only when you recalibrate the odometer to account for a tire size change. If you don’t recalibrate the odometer, bigger tires won’t affect it.
Changing your car’s tire size to bigger ones will not necessarily automatically affect your odometer because you still have to recalibrate it.
However, while the odometer isn’t automatically affected, the actual mileage of your car is affected. Therefore, you need to make sure that you recalibrate your odometer to reflect your car’s actual mileage.
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How do large tires affect odometer reading?
You should know how vital your odometer is to your car as early as now. The odometer is responsible for keeping track of your car’s mileage or the total distance it has traveled since day one.
This is quite important whenever you want to know when you should have your car maintained, but this is even more important when selling your car because buyers base their decisions on the mileage. That’s why the law has specific laws to protect against odometer tampering.
While you may not have tampered with your odometer, the law also requires that you ensure that your odometer shows the correct readings to your car’s actual mileage. And this can be affected by a simple change in the size of your car’s tires.
The tire size can affect the odometer reading because your car’s odometer is calibrated to the size of the stock tires it came with. And we would have to make a quick review of how odometers work for you to understand that.
An odometer works by having a sensor in the transmission of the car’s front tires. This sensor keeps track of the total revolutions made by your tires and then sends the signal to your car’s engine control unit or ECU.
This is where the ECU allows the odometer to calculate the car’s total distance traveled based on the revolutions made by the tires and on an equation that considers your car’s tire size.
After all, the size of the tire is what determines how far the car has traveled because the revolutions that a car makes are essentially the steps that a person takes when he is walking.
Naturally, the larger your steps, the bigger the distance you cover. So, in that sense, the same principle applies to cars as larger tires cover more ground with every revolution they make.
So, when you change your tire size to larger ones, the car will naturally have a mileage that will tick faster because your vehicle is now covering more distances with every revolution its tires are making. As such, odometers on cars with larger tires
are supposed to tick faster.
However, the problem here is that odometers come calibrated to the size of your car’s stock tires. Therefore, changing the tire size won’t automatically change how the odometer is calibrated.
Your car’s odometer will still count the distance traveled using its original calibration. And this could get you into trouble because your vehicle won’t be reflecting its actual mileage.
When you change your car’s tire size to a larger one, you need to have your odometer recalibrated so that it can now calculate the distance traveled based on the new size of your car’s tires. This will allow you to make sure that your car’s odometer is now reflecting its actual mileage.
How do smaller tires affect the odometer?
In the same way, smaller tires also affect the car’s mileage as larger tires do. However, it’s supposed to be the opposite now because smaller tires cover less ground than larger tires.
Your car’s mileage should be moving slower when you have smaller tires instead of larger ones. Also, in the same way, changing your car’s tire size to a smaller one requires that you have your odometer recalibrated to fit the change in the tire size.
And the key here is always to make sure that you don’t use your car before the recalibration because of how your odometer will end up counting miles that aren’t accurate.
Do large tires affect the speedometer?
While the odometer and the speedometer are not directly connected, you need to know that both these instruments rely on the same concept whenever they show the values they are supposed to show.
The speedometer also relies on how many revolutions the tires are making. This means that the size of the tire also affects the way the speedometer works.
From there, it becomes easy to understand changing your tires to a larger size will also require the speedometer to get recalibrated so that it will now calculate the speeds at which the car is going based on the new tire size.
That’s because, again, larger size can affect the car’s overall speed. After all, the larger diameter will make the wheels turn slower. So, in that sense, your speedometer should now reflect slower speeds as long as you recalibrated it based on the tire size change.
Large tire speedometer calibration
So, after changing your tire’s size to a larger one, here is how you can recalibrate the speedometer. Use this calculator to approximately determine whether or not you have correctly recalibrated your speedometer:
Mechanical Speedometer
- Open the hood and locate the transmission. Unscrew the speedometer cable from the transmission and then remove the plate to expose the two gears that drive the speedometer. Look for the drive gear that is mounted inside the transmission. Count the number of teeth on the drive gear and take note of it.
- Measure the car’s diameter from the top of one of the wheels to the bottom. Divide that number by 20,168 to determine the car’s total revolutions per mile.
- Multiply the revolutions per mile by the number of teeth you counted in the drive gear. Then, after that, look for the axle ratio in the documents of your car. Multiply the axle ratio with the number you came up with after multiplying the revolutions per mile with the teeth.
- Divide that number with 1,001. This will give you the number of teeth you need in the new drive gear. Purchase a new drive gear with the number of teeth you calculated and replace the one in the speedometer.
- Put everything back the way it was.
Electronic Speedometer
- Look for the distance of the test drive in your car’s owner’s manual so that you can determine the distance you need to test drive your car to recalibrate its speedometer.
- Press and hold the calibration button on your speedometer. Start the vehicle and then release the button.
- Press the calibration button again and drive the distance needed for your car’s test drive.
- Press the button a third time after traveling the prescribed test drive distance. This will recalibrate the speedometer to fit the new tire size.