Understanding Tire Corrected Mileage
Bigger tires change how far a vehicle moves per wheel turn. The odometer still counts turns as if the stock tire remains installed. A taller tire travels farther each revolution. Your dashboard may understate distance. That makes raw mileage look worse or confusing.
This calculator corrects that problem with a diameter ratio. It compares old tire diameter with new tire diameter. Then it multiplies the indicated trip distance by that ratio. The result is a better estimate of actual distance traveled. It also corrects speed, odometer error, cost per mile, tank range, and yearly fuel impact.
Why Tire Size Matters
A tire marked 265/70R17 has three useful parts. The first number is section width in millimeters. The second number is sidewall height as a percent of width. The final number is wheel diameter in inches. Two sidewalls plus the wheel create total tire diameter. This tool can calculate that value from tire size fields. It can also accept a direct diameter when you already know it.
Using Fuel Data
The most accurate method uses a full tank record. Fill the tank. Reset the trip meter. Drive normally. Fill again. Enter the indicated miles and gallons used. The calculator corrects the trip miles first. Then it divides corrected distance by fuel used. This gives corrected miles per gallon.
Planning Bigger Tire Changes
Bigger tires can affect more than the odometer. They may add weight. They may change gearing. They may add rolling resistance. The optional baseline section compares corrected mileage with your previous mileage. It can estimate annual fuel cost changes. That helps you judge whether the change is practical.
Reading the Results
A positive odometer error means actual distance is higher than shown. A corrected speed of 64 mph at a 60 mph indicated speed means the vehicle is moving faster than the dashboard shows. Use these results for planning only. Confirm speedometer changes with safe testing or a professional scan tool. Tire pressure, tread design, terrain, wind, load, and driving style can change real fuel use. Keep records across several fill ups for the best average. A single tank can be misleading. Compare results after re-gearing or calibration because those changes can alter readings.