The seats are different, too. Integrated seat- belts are neat and the electric headrests drop automatically when you fold the seats forward. The adjustable lumbar support of the coupe's seats is absent but the seat-back and cushion seem to have a tad more padding and the slight aches and pains and 'wriggle factor' present on longish trips in the coupe have been banished. Being heated, they also make top-down cruising on cool evenings a snug affair.

What of the convertible vs coupe debate in terms of actual driving? Simple. In my opinion, this convertible is a better driver's car than the coupe that went before it and no, I can't quite believe it either. I'd better explain.

On the day of swapping cars, I drove up to Hampshire in my coupe and half-an-hour later did the 150-mile trip back in the convertible. The signs on this back-to-back 'test' were not overly propitious, the convertible definitely lacking some of the coupe's rigidity - highlighted by slight kick-back through the steering column, tremors in the rear-view mirror and a generally softer feel, leaving me wondering if the change was such a great idea after all.

However, over the next week or so, a few top-down first-1200-mile running-in cruises over moorland roads in glorious weather, straight six rasp sounding all the better al fresco, put me in a better frame of mind. It was after the car passed that 1200-mile marker and I aimed it down my favourite twisties in anger for the first time that the surprise came. Turning in to apexes is more immediate and eager and flick-flacking through combinations of bends more fluid than in the coupe before it. Even more surprising, the convertible holds its line more securely through poorly surfaced medium-speed corners which had its predecessor skipping off-line by a foot or so. Only on faster, three-figure- plus smooth sweepers does the convertible seem to lose out, needing occasional tiny steering inputs where the coupe tracked totally true.

I'm pretty sure the wheels are the reason for all this. Despite dire warnings from the entire evo team, who insisted that standard 18s were the wheel of choice, I put bigger 19s on the coupe. The convertible rides on 18s. A knowing nod from a well-known racing driver and M3 owner I was chatting to recently convinced me I'm right, but just to be sure I'm meeting up with a couple of coupe owners next week - one on 19s, one on 18s. I'll let you know the result.