We've discussed the nomenclature shift here in quite some detail so I'm not going to dive into the history and legacy BMW is throwing away by filling a number in their naming system. No today is all about the actuall differences BMW gave us between the 3 and 4 series.
The 4 series has more to its identity than the number four. Dimensionally the 4 series is unique from its sedan brethren. The 4 series coupe shares a 110.6 inch wheelbase with the 3 series, but that is where chassis similarities cease. The 4-series is a half inch wider in the front track and 0.8 inches wider in the rear. widening the coupe allow the 4 series to sit 2.1 inches lower than the 3 series. BMW claims that the 4-series has the lowest center of gravity of all BMWs currently on sale. The 4 series wider and lower dimensions also give the coupe a sleeker look and feel compared to the sedan.
The lower and wider 4 series isn't simpley a beauty queen either, its sleeker dimensions should give the 4 series tenacious grip and a ferocious attitude in the corners..
Unlike most of the industry BMW has left the 6-speed MT as a no-cost option.