IT wasn't that long ago that choosing a BMW was a game of very few numbers. There was the three-series and five-series for the mainstream, and then the six, seven and occasional eight series for the privileged few.
Recently, though, BMW has been filling in the gaps. There's a one-series, a two-series, a three series, a four-series and the sixes, sevens and even the eights are firmly back in the line-up.
Broadly speaking, the bigger the number, the bigger the car.
The one-series is small, the seven-series is big. The three-series is fairly middle-of-the-road – we all know about that one – and the four-series is the two-door version of the three-series.
Except now there's a five-door version of the two-door model from the three-series.
Confused? I'll try and simplify it. The five-door version is a new variant of the four-series and it's called the Gran Coupe. It's still, at least in BMW's book, a coupe but it has four passenger doors and a hatchback-style tailgate.
This newcomer is essentially BMW's answer to the growing demand for coupe versions of existing saloons – think Volkswagen Passat CC, Mercedes CLS, Audi A5 Sportback and so on.
So, if I haven't lost you entirely by this point, it's a four-series coupe with a couple of extra doors and a rear hatch which, remarkably, all fits in to the same footprint of the two-door coupe.
And, even more remarkably, fitting all this into a car the same length as the two-door version doesn't make it feel cramped in any way.
Up front it's largely the same, barring the smaller, pillarless doors, and in the back it obviously has quite a low roofline but there's room for a 6ft adult (just) and respectable legroom.
Being a chopped-about facsimile of the four-series coupe, the engine range is identical with four-cylinder petrol and diesel models, along with a couple of six-cylinder flagships.
The most popular engine is likely to be the two-litre diesel as fleet buyers will be queuing up for this car, but the pick of the bunch is almost certainly the petrol-powered 428i.
In pursuit of strong economy figures, BMW has developed an engine that would normally have a couple of extra cylinders and coaxed 245bhp out of it.
At the top end of the rev-range it's a tad noisy perhaps, but it's a very nice, throaty noise sporty drivers will enjoy and it propels the car with as much force as you'll ever need.
It drives well too. This being based entirely on the coupe's underpinnings, there's no detriment in the road manners from adding on a couple of doors.
You can opt for sports spec, or luxury spec and settings in either can be changed to alter the suspension, responses and gear changes. The balance is near-perfect and it grips well through the corners.
In either guise, you can opt to add all sorts of upgrades at the point of purchase, including four-wheel-drive on some models, but the Gran Coupe comes loaded with plenty of freebies in a bid to help it fight off advances from its closest rival, the Audi A5 Sportback.
However, unlike to the Audi, or more noticeably when parked next to the VW Passat CC or the Mercedes CLS, one of the few things I can find to fault the Four-series Gran Coupe is that it doesn't stand out enough as an individual model.
While the Passat and CLS are penned in a swoopy way to mark them out, almost to the point of being over-styled, the Gran Coupe lacks a bit of flair in my opinion. It's not unattractive, but it somehow feels like the designers have played it safe with the styling.
That won't bother everyone and what you do get is a coupe with typical, fine BMW handling, plenty of room in the back and a decent boot in a car no bigger than the two-door coupe on which it is based.
It's a great new model in a long line-up of variations which BMW has, somehow, found a slot for.