The car uses a much wider front track with a 275 section tyre (it used to be a 245). (evo.co.uk)
The demonstration models feature an advanced chassis configuration with a narrow front track and wider rear track for optimum aerodynamic efficiency and handling stability. (greencarcongress.com)
It's also a distinction between the 4 - and the 3 - series, as rear track, which is wider than front track in the 4. (automobilemag.com)