Do Bigger Tires Change Your Odometer Reading?

Yes. A taller tire makes your odometer count fewer miles than you really drive, by the same percentage that the tire is taller. Going from 245/75R16 to 265/75R16 makes the tire 3.88% taller, so every 10,000 miles on the odometer are about 10,388 real miles.

A shorter tire does the opposite: the odometer counts more miles than you drive. This guide shows the formula, a worked example and a table of common size changes.

Why does tire size change the odometer?

The odometer does not measure the road. It counts how many times the wheels turn and multiplies that by the distance the original tire covers in one turn. That distance was set at the factory for the original tire size.

A taller tire covers more road in one turn. The car still counts each turn as the old, shorter distance, so the miles on the odometer fall behind the real miles. The speedometer uses the same wheel-turn signal, so it reads low by the same percentage. See how to calculate speedometer error after a tire size change.

How do you calculate the real mileage?

1. Overall diameter of each tire (mm) = rim x 25.4 + 2 x width x aspect / 100.
2. Ratio = new diameter / old diameter.
3. Real miles = odometer miles x ratio.

Example: 245/75R16 to 265/75R16

1. 245/75R16: 16 x 25.4 + 2 x 245 x 0.75 = 406.4 + 367.5 = 773.9 mm (30.47 in).
2. 265/75R16: 406.4 + 2 x 265 x 0.75 = 406.4 + 397.5 = 803.9 mm (31.65 in).
3. Ratio: 803.9 / 773.9 = 1.0388. The new tire is 3.88% taller.
4. 10,000 odometer miles x 1.0388 = about 10,388 real miles.

In wheel turns: the 245/75R16 turns about 661.9 times per mile and the 265/75R16 about 637.2 times. The car still divides by the old number, so it counts each real mile as 0.96 miles.

Over 50,000 odometer miles the gap is about 1,938 miles. If you change oil every 5,000 odometer miles, the engine has really run about 5,194 miles at each change.

To run these numbers for your own sizes, enter both in the tire size calculator.

How much do common size changes shift the odometer?

Table 1 uses nominal diameters from the formula above. "Real miles" is what the vehicle has driven when the odometer shows 10,000 miles.

The reverse works the same way. Going from 265/70R17 down to 245/70R17 makes the tire 3.49% shorter, so the odometer counts more miles than the vehicle drives.

What does the mileage gap affect?

• Service intervals. Oil changes and other services based on odometer miles happen later in real miles.
• Fuel economy. If you calculate miles per gallon from odometer miles, the result is lower than the real figure by about the same percentage.
• Mileage records. Warranty, lease and sale records use the odometer number. Keep a note of the date and the odometer reading on the day you changed tire size.
• Tire wear itself. A worn tire is slightly shorter than a new one, so the odometer error is a little smaller near the end of the tire's life.

How can you check your own odometer error?

The formula uses the size printed on the tire. Real tires differ from it by a small amount, depending on brand, model, load and air pressure. To measure your own vehicle, drive a known distance, such as 10 miles between highway mile markers or a route measured with a GPS app, and compare it with the trip meter. Divide the real distance by the trip-meter distance to get your ratio.

Frequently asked questions

Do bigger tires add miles to the odometer?

No. Taller tires make the odometer add fewer miles than you drive. Shorter tires make it add more.

Can the odometer be corrected after a tire size change?

On many vehicles the tire size setting can be changed with a dealer tool or an aftermarket programmer. Whether your vehicle allows it depends on the make and model. Ask your dealer.

Is a small change, like 1%, worth worrying about?

A 1% change adds up to about 100 miles per 10,000. It is small for daily use, but it still shifts service intervals and mileage records. Compare sizes that stay close to the original with the tire size alternatives tool.