Corrected Fuel Economy Calculator
Correct dash fuel economy for a tire size change. Convert indicated mpg, L/100 km and km/L into true values with one factor.
Adjust distance-based fuel economy readings.
Corrected Fuel Economy Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Corrected Fuel Economy Calculator Works?
The Corrected Fuel Economy Calculator works by correcting the distance part of the fuel economy reading and leaving the fuel volume unchanged. The tool uses 3 steps.
Set the correction
Enter both tire sizes or a correction factor, for example 1.0349.
Enter the reading
Type the indicated economy in mpg (US), mpg (UK), L/100 km or km/L.
Read the true economy
The calculator multiplies mpg and km/L by the factor, divides L/100 km by the factor, and shows all units.
Corrected Fuel Economy Calculator Formula
The Corrected Fuel Economy Calculator formula is MPG_true = MPG_indicated × CF, and L/100 km_true = L/100 km_indicated ÷ CF.
mpg_true = mpg_ind × CF ; km/L_true = km/L_ind × CFL/100km_true = L/100km_ind ÷ CFL/100 km = 235.215 ÷ mpg- CF
- Correction factor OD_new ÷ OD_cal
- 235.215
- Conversion constant for US gallons
Worked example
A truck with a CF of 1.0349 shows 18 mpg (13.1 L/100 km). True economy is 18.6 mpg (12.6 L/100 km). The taller tires look 3.4% worse on the dash than on the road.
Corrected Fuel Economy Calculator Conversion Table
The Corrected Fuel Economy Calculator conversion table converts 7 indicated readings into true mpg, L/100 km and km/L for a +3.49% tire upsize.
| Indicated | True mpg (US) | True L/100 km | True km/L |
|---|---|---|---|
| 15 mpg (15.7 L/100 km) | 15.5 mpg | 15.2 L/100 km | 6.60 km/L |
| 18 mpg (13.1 L/100 km) | 18.6 mpg | 12.6 L/100 km | 7.92 km/L |
| 20 mpg (11.8 L/100 km) | 20.7 mpg | 11.4 L/100 km | 8.80 km/L |
| 25 mpg (9.4 L/100 km) | 25.9 mpg | 9.1 L/100 km | 11.00 km/L |
| 30 mpg (7.8 L/100 km) | 31.0 mpg | 7.6 L/100 km | 13.20 km/L |
| 35 mpg (6.7 L/100 km) | 36.2 mpg | 6.5 L/100 km | 15.40 km/L |
| 40 mpg (5.9 L/100 km) | 41.4 mpg | 5.7 L/100 km | 17.60 km/L |
What is Corrected Fuel Economy Calculator?
A Corrected Fuel Economy Calculator is a tool that fixes the distance error inside a fuel economy reading after a tire size change. Fuel economy equals distance divided by fuel, and the distance comes from the same sensor as the odometer.
Taller tires make a vehicle look less efficient than the vehicle really is. Part of the apparent drop after an upsize is measurement error, not real fuel loss.
Real fuel use often rises with larger tires as well, from added weight, rolling resistance and aerodynamic drag. The corrected figure separates measurement error from that real change.
What are the uses of Corrected Fuel Economy Calculator?
There are 4 main uses of the Corrected Fuel Economy Calculator, including before-and-after comparisons and fleet reporting.
Before-and-after comparisons
Compare fuel use before and after a tire change on equal terms.
Fleet reporting
Report true fuel economy for vehicles with non-stock tires.
Fill-up logs
Correct hand-calculated economy from fuel receipts and trip readings.
Tire choice
Measure the real fuel cost of an all-terrain upgrade.
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