23 MPG combined isn’t going to win any fuel economy awards, but for the 2015 BMW 640i xDrive Convertible with its smooth 3.0L inline-six and all-wheel drive, it’s a reasonable compromise. This isn’t a car bought by someone prioritizing lower fuel costs above all else. It’s for the affluent driver who wants open-air thrills, effortless performance, and the prestige of the BMW badge, even if it means accepting a slightly higher fuel bill.

City and highway performance

The EPA ratings for the 2015 640i xDrive Convertible break down to 20 MPG in the city and 29 MPG on the highway. The city number reflects stop-and-go traffic, where the car’s weight and the need to constantly accelerate impact fuel consumption. The highway figure is more respectable. Driven carefully on long stretches of open road, the 640i can approach its EPA estimate, thanks to its well-engineered eight-speed automatic transmission that keeps the engine at relatively low RPMs at cruising speeds. That automatic is key to how this car balances performance and economy, and it helps the 640I MPG across all years stay reasonable.

Annual fuel cost

According to the EPA, the annual fuel cost for the 2015 BMW 640i xDrive Convertible is estimated at $2,500. This figure is based on driving 15,000 miles per year, with 55% of those miles driven in the city and 45% on the highway. It also assumes gasoline priced at the national average. This is just an estimate; your actual fuel costs will vary based on your driving habits, the type of fuel you use, and local gasoline prices. Still, $2,500 offers a useful benchmark when considering the overall cost of ownership.

Real-world expectations

While the EPA figures provide a baseline, real-world fuel economy often differs. Drivers who accelerate hard or frequently the engine’s ample power will likely see figures below the EPA estimates. Those who accelerate smoothly and maintain consistent speeds can often match or even slightly exceed the highway MPG number. Traffic conditions, weather, and tire pressure also play a role. Expect a range, and understand that the 640i’s performance can tempt you to dip into the lower end of that range.

How it compares

The 2015 BMW 640i xDrive Convertible sits in a competitive segment. The Mercedes-Benz SL450 from the same year posts a slightly better 20 MPG city and 30 MPG highway, giving it a small edge. However, the Jaguar F-Type V6 Convertible, while thrilling to drive, achieves only 19 MPG city and 27 MPG highway, making the BMW seem relatively frugal. All Bmw fuel economy data shows this car is right in line with the other performance models. For the buyer considering a car like this, the differences of a few MPG often take a backseat to factors like styling, performance, and brand image.

Tips to maximize efficiency

Use the 640i’s driving modes. Selecting “Eco Pro” mode will remap the throttle response and shift points to prioritize fuel efficiency over outright performance. This can be helpful during city driving or on long highway stretches where maximum power isn’t needed.

Ensure your tires are properly inflated. Underinflated tires increase rolling resistance, forcing the engine to work harder and reducing fuel economy. Check your tire pressure regularly and maintain the recommended PSI listed on the driver’s side door jamb.

Avoid hard acceleration and braking. Smooth, gradual inputs are easier on your tires and brakes and contribute to better fuel efficiency. Anticipate traffic flow and maintain a consistent speed whenever possible.

Minimize idling. If you’re stopped for more than a minute or two, turn off the engine. Modern engines are designed to restart quickly and efficiently, and idling wastes fuel unnecessarily.

Keep up with scheduled maintenance. A well-maintained engine runs more efficiently. Follow the recommended maintenance schedule for your 640i, including regular oil changes, air filter replacements, and spark plug inspections.