Does tire pressure really affect your gas mileage?
Yes, but for most drivers not by much: the EPA's own average is 0.6%, up to 3% in some cases. The bigger cost of low tires is not the gas, it is the tread they wear through faster.
Where the number comes from
0.2% per psi, on averageThe Department of Energy measured it directly: gas mileage drops about 0.2% for every 1 psi the average of all four tires sits under spec. A car 8 psi low across the board loses roughly 1.6%, which on a $1,700 yearly gas bill is about $27.
Most cars aren't 8 psi lowA slow, unnoticed leak or a cold snap can get you there over a season. That is why the EPA's real-world average, across drivers who check sometimes and drivers who never do, lands at 0.6%, not a bigger number.
Tread wear costs more than the gasA tire that runs low for months wears out thousands of miles sooner than one kept at spec. A $150 to $250 tire replaced a year early costs more than several years of the mileage penalty.
What underinflation actually costs
| Tires vs. spec | Mileage effect | Cost, $1,700/yr gas bill |
|---|---|---|
| At spec (checked monthly) | 0% | $0 |
| 2 psi low, average | -0.4% | ~$7/yr |
| 8 psi low, average (a season of not checking) | -1.6% | ~$27/yr |
| Properly inflated after running low | +0.6% avg, up to 3% | up to ~$51/yr back |
Department of Energy Fact #826 (0.2%/psi) and fueleconomy.gov (0.6% average, up to 3%). Dollar figures are this table's own math against a 25 mpg car doing 12,000 miles a year at $3.50/gal, not a site default; run your own car on Fill up.
Check it right
- Use the door-jamb sticker, not the tire sidewall. The sidewall number is the tire's maximum rating. Your car's recommended pressure is on a sticker inside the driver's door.
- Check cold. Driving warms the air inside a tire and raises the reading; check first thing, before the car has moved that day.
- Check monthly, and before a long trip. A season's temperature swing alone can move pressure several psi.
Questions people ask
Does tire pressure really affect your gas mileage?
Yes, but for most drivers not by much. The EPA puts the average gain from keeping tires at the right pressure at 0.6%, up to 3% in some cases. The effect is small at a few psi low and grows the longer a tire runs underinflated.
How much gas do I lose per psi of underinflation?
About 0.2% of your gas mileage for every 1 psi the average of all four tires sits below spec, per Department of Energy testing. A car 8 psi low across the board loses roughly 1.6%. A single tire that is badly low, from a slow leak nobody noticed, can cost more than that on its own.
How do I know if my tires are underinflated?
Check monthly with a tire gauge against the sticker inside the driver's door jamb. Do not use the number on the tire's own sidewall; that is the tire's maximum rating, not your car's recommended pressure. Check cold, before the car has moved that day.
Does overinflating help even more?
A little, but it is not free money. Overinflated tires wear the center of the tread faster, ride harsher, and grip worse in the wet, so the small mileage gain is usually not worth the tradeoff. Stick to the door-jamb number.
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