Running costs
Tire size and fuel economy
There is no reliable universal fuel-economy percentage for a tire-width change. Several mechanical effects move together.
Separate rolling resistance from dimensions
Compound, tread, construction, inflation pressure and load affect rolling resistance. A wider or heavier assembly can change energy use, but width alone cannot tell you by how much. Use comparable tire data where available and follow the vehicle’s pressure guidance.
Watch the distance measurement
A tire-size change can affect odometer distance as well as speed. If distance is under-recorded after fitting a larger tire, a fuel-economy calculation based on that distance can look worse even before any physical efficiency change is assessed. Correct the measurement basis before comparing tanks.
Run a scenario rather than inventing a prediction
At 12,000 km/year and a fuel price of 1.50 per litre, 12 km/L costs 1,500 per year. If measured economy later becomes 11.5 km/L, cost becomes 1,565.22. That 65.22 difference is a scenario calculation, not a predicted effect of any tire size.
Method and references
Examples use nominal geometry and fixed-price scenarios, with no vehicle-specific specifications implied. See our calculation methodology and editorial policy.
Unit reference: NIST Guide to the SI: conversion factors. Financial examples are arithmetic illustrations, not market-price forecasts.