About the BMW - contenued
In 1972, the 5 Series was launched to replace the New Class sedans, with a body styled by Marcello Gandini. The New Class coupes were replaced by the 3 Series in 1975, and the New Six became the 7 Series in 1977. Thus the three-tier sports sedan range was formed, and BMW essentially followed this formula into the 1990s. Other cars, like the 6 Series coupés that replaced the CS and the M1, were also added to the mix as the market demanded.

The current BMW model line-up is split into what they call "Series", traditionally identified by a single digit - e.g. the 3 Series.

In 2004 BMW announced plans to make odd-numbered models sedans and estates or wagons (BMW calls its estates/wagons Touring models), while even-numbered models will be two-door coupes and cabriolets. This convention started informally in 1976 with the introduction of the 6 Series and later continued in 1989 with the 8 Series, but died off when the latter was discontinued in 1999. This practice was revived as the Z4 replaced the aging Z3 roadster in 2003 and continues as the new 6 Series augments the existing BMW 5 Series.

Coupe versions of the 3 Series sedans have always been named 3 Series vehicles, as well. The company had considered renaming future 2-door derivatives of the 3 Series as 4 Series cars, but this plan has reportedly been shelved. more [...]