The EPA publishes a city figure and a highway figure. Buyers usually glance at the combined number and move on. The distance between the two is where the interesting part is.
| Cylinders | City | Highway | Gap |
|---|---|---|---|
| 3 | 30.6 | 36.8 | +20% |
| 4 | 22.5 | 28.9 | +29% |
| 6 | 16.8 | 23.1 | +38% |
| 8 | 13.6 | 19.0 | +39% |
| 12 | 11.2 | 17.4 | +56% |
The gap nearly triples across the range
A three-cylinder gains 20% moving from town to motorway. A twelve-cylinder gains 56%.
Put another way: the big engine is disproportionately punished by traffic. Its highway figure looks survivable; its city figure is where the real bill comes from.
Why size makes the gap worse
Idling costs the same regardless of speed. A large engine burns considerably more fuel sitting still than a small one, and city driving is full of sitting still.
Acceleration moves mass. Stop-start driving means accelerating the car repeatedly, and large engines are fitted to heavy vehicles. Every launch from a red light costs more.
Efficiency arrives at steady speed. Big engines are most efficient at a light, constant load — precisely what a motorway provides and a city never does.
Small engines are already working hard. A three-cylinder is closer to its optimal load at low speeds, so it has less to lose.
Fuel grade compounds it
Sorted by fuel type instead, premium-petrol cars show the widest gap of any combustion category at +40%, against +31% for regular and +29% for diesel.
Premium is specified on larger and performance engines, so this is the same effect seen from another angle — with the added detail that the fuel itself costs more per gallon. A city-driven premium car pays twice.
Diesel has the narrowest gap of the combustion fuels and the best city figure at 21.7 mpg, which is why diesels remain the efficient choice for stop-start commercial work.
Which number should you use?
Work out your actual split. If your driving is 80% urban, the combined figure overstates what you'll get, and it overstates it more the bigger the engine.
The gap changes what the right car is. Between two vehicles with similar combined ratings, the one with the smaller gap is the better city car — the combined number hides that entirely.
Engines matter more than badges. A single model year can be rated 18 mpg apart across its powertrain options, as we found in two 2025 Civics can differ by 18 mpg. The engine a specific car was built with is encoded in its VIN, and a VIN check decodes it.
We priced what each cylinder step costs annually in each pair of cylinders adds $900 a year.
Frequently asked questions
Why is city fuel economy so much worse than highway?
Idling burns fuel at any speed, stop-start driving means repeatedly accelerating the car's mass, and engines are most efficient at steady light load. The gap runs from 20% on a three-cylinder to 56% on a twelve-cylinder.
Do bigger engines suffer more in traffic?
Considerably. Four-cylinder engines lose 29% moving from highway to city, V8s 39% and V12s 56%. Large engines idle expensively and are fitted to heavy vehicles that cost more to accelerate from every stop.
Which fuel type handles city driving best?
Diesel, with the narrowest combustion gap at 29% and the best city figure at 21.7 mpg. Premium-petrol vehicles have the widest gap at 40%, and pay more per gallon on top of it.
Should I use the city or combined MPG figure?
Work out your own split. If most of your driving is urban, the combined figure overstates what you'll achieve — and it overstates it more the larger the engine. Between two cars with similar combined ratings, the one with the smaller gap is the better city car.
Denis Kataev is a serial solopreneur and the founder of ForCar. With 15+ years in software engineering and 10 years in SEO, he builds data-driven products end to end — backed by a sharp eye for design. At ForCar he mines proprietary vehicle datasets, turning raw numbers into buying advice you can actually trust.
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