The Impala is a large, front-wheel drive sedan that comes in three different models ranging from simple to sporty. The base Impala LS comes with a 211-horsepower, 3.5-liter pushrod V6 engine, as does the mid-level LT. Standard on the top-of-the-line LTZ is a 230-horsepower, 3.9-liter V6. With either of the engines, a responsive 4-speed automatic is the only transmission offered, and both V6s provide perfectly adequate performance for keeping up with traffic, even when fully loaded. Additionally, both engines come with flex-fuel capability to accommodate up to 85% ethanol. LS and LT models come with suspension settings that favor ride quality but provide good handling control, with rack-and-pinion steering, front MacPherson struts, and stabilizer bars front and back, with 16- or 17-inch wheels and tires. On these models, the ride is especially quiet and well isolated. The LTZ adds larger stabilizer bars, a sportier suspension tuning and W-rated 18-inch performance tires. The Stabilitrak stability control system is standard on all Impalas, as are six airbags, including side thorax airbags for front-seat occupants and full-length side-curtain airbags. Four-wheel anti-lock disc brakes are also included on all Impala models, and OnStar is included as standard on all Impalas for the first year. The Impala's interior makes the most of available space, with plenty of legroom for front and rear occupants and enough space in back for two adults of nearly any size to be comfortable, but there is room for three. LATCH child-seat tethers are included in all three rear seating positions. Available on LT and standard on LTZ models is a flip-and-fold-flat rear seat, which allows a continuous loading space through the trunk. The Impala is also one of the few remaining cars in its class to offer an available front bench seat, to accommodate three across and six people total. Base LS models come with most of the conveniences buyers expect, including power windows, keyless entry, cruise control and air conditioning, plus dual-zone manual climate control and a 6-speaker CD sound system with XM Satellite Radio. LT models get a number of appearance enhancements, plus a remote start system, cast aluminum wheels and foglamps. LTZ models are the most luxurious and bring a long list of extras like heated seats, a universal garage door opener, Bluetooth hands-free calling, steering-wheel audio controls and a Bose 8-speaker sound system. Nuance leather upholstery with French seams is also included. All sound systems feature an auxiliary input jack for other sources such as iPods. Convenience and Luxury packages are available on the LT, and include many of the amenities found on the LTZ, such as Bluetooth, universal remote, heated seats, heated power mirrors and the Bose stereo. Stand-alone options on the LTZ include a power sunroof and a dealer-installed dual-screen rear DVD system.