The Mazda6 comes in two different model lines, designated by their respective engines. Economy-minded "I" models get a 170-horsepower, 2.5L 4-cylinder engine, while sportier "s" models come with a 272-hp, 3.7L V6. The base 4-cylinder comes with plenty of power to move the Mazda6 quickly in almost all driving conditions, but the V6 brings truly authoritative performance and the smooth character of a luxury sedan; Mazda says that it's the most powerful V6 in its class. A 5-speed automatic transmission is optional on the 4-cylinder version, while all V6 models come with a 6-speed automatic. Both automatic transmissions come with a manual shift mode and have adaptive shift control, which downshifts automatically around tight corners or steep slopes. The Mazda6 has an absorbent but relatively firm ride, and compared to most other mid-size sedans it has more responsive handling, while also permitting a very tight turning circle for easier parking. Interior space is vast, with enough headroom and legroom in the back seat for all but the largest adults despite the sportier, rakish styling. Trunk space is the largest in the mid-size sedan class, according to Mazda, at 16.6 cubic feet, and the rear seatbacks fold forward. Fuel economy estimates are up to 21 mpg city, 30 mpg highway with the automatic transmission and 4-cylinder engine, and 17/25 for the V6. The base Mazda6 i is one of the lowest-priced mid-size sedans and includes air conditioning, power locks and windows, a tilt/telescope steering wheel, a height-adjustable driver's seat and split folding rear seat, among other features. Safety equipment on all models of the 6 includes front side airbags, side-curtain airbags, anti-lock brakes and electronic stability control. Bumpers are rather tall for a sedan, to help reduce minor parking lot damage from taller SUVs. The Mazda6 i Sport adds keyless entry, cruise control and steering-wheel-mounted controls, while the i Touring includes a CD changer, leather trim, fog lamps, a power driver's seat and larger 17-inch alloy wheels. V6 s Touring and s Grand Touring models add extras like dual-zone climate control, Bluetooth and a Bose Centerpoint surround-sound system, plus showier 18-inch wheels. A Tech Package adds a push-button start system and advanced keyless entry, along with a multi-information display.