Find your real cost per mile and annual fuel spend. Compare two vehicles, or regular vs premium, side by side.
The real cost of fuel isn't just the price at the pump - it's the price divided by your fuel economy. A car with 15 MPG costs the same per mile as a car with 30 MPG if the 30 MPG car uses premium at twice the price.
Premium (91-93 octane) is required for many high-performance engines - using regular can trigger knock retard, which reduces both power and efficiency. However, if your car's ECU can safely adapt to 87 octane, the savings may not justify the switch.
A car that gets 25 MPG on premium at $4.29/gal costs 17.2Ā¢/mi. The same car on regular at $3.79/gal is 15.2Ā¢/mi. At 15,000 miles per year, that's $300/year. If knock retard costs you 5 MPG (dropping to 20 MPG), the "savings" evaporate - you're now spending $189 more per year using regular.
EPA estimates typically overstate real-world fuel economy by 10-20% for performance cars, especially in urban driving or spirited use. If your car is rated 22/32 MPG, budget for 18-20 MPG in mixed driving. Track or autocross days can push consumption to 10-14 MPG regardless of the EPA rating.
E85 contains about 30% less energy than gasoline per gallon. At the same pump price, you'd need E85 priced at least 30% below regular for it to break even on fuel cost alone - not counting the power gains from tuning for E85's higher octane rating.
Related Calculators