23 MPG combined isn’t exactly “eco-friendly,” but for the 2018 BMW 640i Convertible, it’s a compromise its target buyer accepts. This isn’t a car for maximizing gas mileage; it’s a statement, a reward, an open-air experience powered by a refined inline-six. The 640i Convertible suits those who value luxury, performance, and the joy of driving with the top down, and they’re prepared to pay for it, at the pump and elsewhere.

City and highway performance

The EPA estimates the 640i Convertible at 20 MPG in the city and 29 MPG on the highway. The city figure reflects stop-and-go traffic and the engine’s power delivery. The highway number is optimistic, achievable during steady cruising. The eight-speed automatic transmission helps, keeping the engine in its sweet spot for performance and efficiency. A heavy foot, common in a car that begs to be driven aggressively, will quickly reduce those highway mpg numbers. The 640i’s curb weight of around 4,300 pounds will also impact its real-world figures.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2018 BMW 640i Convertible at $2,500. This is based on driving 15,000 miles per year and assumes fuel prices align with national averages. Actual fuel costs will vary depending on individual driving habits, local fuel prices, and the type of fuel used. The 640i requires premium fuel, so expect to pay more per gallon than the national average. The $2,500 figure is a useful benchmark, but tailor it to your specific circumstances.

Real-world expectations

While the EPA estimates provide a baseline, real-world fuel economy for the 640i Convertible will vary. Owners reporting their figures on sites like Fuelly demonstrate a range. Some meet or exceed the EPA’s combined estimate, while others fall short, especially those in urban areas or with spirited driving habits. Expect to average closer to 21-22 MPG in mixed driving conditions. To help with your expectations, you can find more data about 640I MPG across all years.

How it compares

Compared to other luxury convertibles of its era, the 640i’s fuel efficiency is in the middle. The Mercedes-Benz E400 Cabriolet from the same year, with its similar turbocharged six-cylinder engine, achieves a nearly identical 23 MPG combined rating. The Audi S5 Cabriolet, boasting a supercharged V6, manages a slightly better 24 MPG combined. The V8-powered BMW M6 Convertible sees a significant drop-off to just 17 MPG combined, a price many performance enthusiasts accept for the added power and sound. A prospective 640i buyer likely cross-shops these vehicles, weighing fuel economy against brand prestige, styling, and driving dynamics. For more data, check all Bmw fuel economy data.

Tips to maximize efficiency

Use the 640i’s “Eco Pro” driving mode. It might dull throttle response, but it optimizes engine and transmission settings for fuel efficiency, particularly during steady cruising. It also enables coasting, decoupling the engine from the transmission when you lift off the accelerator.

Monitor your tire pressure regularly. Underinflated tires increase rolling resistance, impacting fuel economy. The 640i’s tire pressure monitoring system can alert you to pressure drops, but proactive checks are always recommended.

Anticipate traffic flow and avoid unnecessary hard acceleration and braking. Smooth, consistent driving is important for maximizing fuel efficiency in any vehicle, and particularly important in a performance-oriented car like the 640i.

Limit idling. Modern engines are designed to be more efficient when turned off than when idling for extended periods. If you anticipate stopping for more than a minute or two, turn off the engine.

Keep the top up when possible at higher speeds. More drag from driving with the convertible top down reduces fuel efficiency, especially above 50 mph. Reserve top-down driving for leisurely cruises at lower speeds to maximize both enjoyment and fuel economy.