| April 12, 2010 |  |
New Luxury Hybrids Demonstrate Value of Downsizing Gas Engines
WASHINGTON (April 12, 2010) — In the first update to their Hybrid Scorecard, auto engineers at the Union of Concerned Scientists (UCS) found that the BMW ActiveHybrid X6 squanders its hybrid drivetrain on boosting power, while the Mercedes-Benz S400 hybrid achieves some success in lowering costs by combining its relatively weak hybrid drivetrain with a downsized conventional gasoline engine.
BMW's first hybrid, the luxury ActiveHybrid X6 is a "muscle hybrid." BMW layered the car's hybrid drivetrain on an already powerful eight-cylinder engine to boost performance, giving it the highest horsepower and torque of any hybrid on the market. By contrast, the new Mercedes-Benz S400 Hybrid, also the company's first hybrid, went from an eight-cylinder to six-cylinder engine compared with its base model.
Downsizing the S400's engine provided significant cost savings and the bulk of its fuel economy improvement over the conventional S550. The S400 Hybrid actually costs less than the S550, a first for a hybrid. The S400 Hybrid is a mild hybrid, which means that it has a hybrid drivetrain, regenerative breaking and its gas engine shuts off when the vheicle is stopped, but it can not run on electric power alone. Notably, it is the first production hybrid that uses lithium-ion batteries, which provide greater energy storage per pound than conventional batteries.
Despite its hybrid label, the BMW ActiveHybrid X6 performs far worse from an environmental perspective than the only other midsize luxury hybrid SUV on the market, the Lexus RX 450h. UCS gave the X6 a low environmental score of 4.4 out of 10, but gave the RX450h a 7.4 rating.
The X6 comes with $10,000 of "forced features," including a deluxe sound system and other features not included in its base model. The S400, conversely, has no forced features compared with its base model. While both cars are already quite expensive luxury vehicles, UCS's initial Hybrid Scorecard analysis found that forced features unnecessarily drive up the cost of hybrid cars across vehicles classes.
The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with citizens across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.
