Both the 128i and the 135i come as coupes and convertibles, but not as four-door sedans as 3 Series.
The 1-Series cars use the same engines and transmissions as the bigger and heavier 3-Series. The 1-Series base car, the BMW 128i, has a 3.0-liter, 230-horsepower inline six-cylinder engine. The BMW 135i has a 3.0-liter inline six-cylinder, too, but with twin turbochargers, pumping out 300 horsepower, the same engine found in the BMW 335i.
Both offer six-speed manual or automatic transmissions.
The 135i has a standard sport-tuned suspension that is firmer than the suspension on the 128i. The 1 Series uses the same set up as the 3 Series with an aluminum double-pivot front suspension and a five-link fully independent rear.
Both are the same size. Compared to BMW 3-series they are about 9 inches shorter, wheel base is four inches shorter and the car's width is two inches less.
Compared to the 3 Series coupe, the 1 Series features a more upright grille and a C-pillar that's not as sleekly styled. From the outside, both 1 Series coupe trims look quite similar, but the 135i is more sporting, outwardly identified by the larger standard 18-inch tires and wheels, compared with the 128i's 17-inchers. The 135i also gets a standard rear spoiler and an "aerodynamic kit" for the lower body. Xenon headlights with an auto-leveling feature are standard on the 135i, optional on the 128i. One of the biggest differences between the 1 and 3 Series is in their looks. The 3 Series looks classic and regal. The 1 Series does not.
Front seats in 1 Series are firm and supportive. Rear seats are best left for sub-5-footers.
The 128i starts at $28,600, and the 135i starts at $34,900 and 3 Series start at about $40000.
There are 11 available exterior colors for 1 Series, but only three are free, and the other eight cost $475 each.
Click here to read why BMW 1 Series might not succeed.