WITH summer now officially with us and the sun making more regular appearances, many car buyers' thoughts go towards open-top motoring.

Wind-in-the-hair offerings come in all shapes and sizes from Alfa Romeos to Mazdas and Mercedes Benz to Bentleys and most car manufacturers offer at least one convertible option in their range.

While some of those stick to more traditional soft tops, more and more are now going down the road of folding tin-tops.

German premium brand BMW went down this route when they introduced an electrically-operated folding metal roof in place of a canvas top in their current Z4.

This feature turned their two-seater into something of a Jekyll and Hyde character, for roof up it is a stunning sports coupé, while at the touch of a button it changes into an open sports car which is about as good as you can get.

On its introduction in 2009, three six-cylinder petrol engines were set aside for the Z4 range: a 2.5-litre 200bhp offering and two three-litre units producing either 255 or 306bhp.

It was the range-topping, twin-turbocharged 35i model, complete with optional seven-speed semi-automatic gearbox I had the good fortune to get to grips with while the weather was going through a nice, warm spell.

Pumping out 306 horses at 5,800rpm, the BMW could power its way from standing to 62mph in just a tad over five seconds and it could keep on powering on until the electronic speed limiter kicked in at 155mph.

It produced 400Nm of torque from a low 1,300rpm for effortless acceleration, yet returned a combined fuel consumption figure in excess of 30mpg.

Hood down, climate control turned up a little to keep any chill at bay, it doesn't get much better than to be behind the wheel of a Z4.

Roof down on a motorway blast, there was little road or wind noise to spoil things with the windows up, while there was also little wind buffering to make things uncomfortable.

Out on the secondary roads the Z4 also handled a dream, with masses of grip giving a real sense of security.

But what really impressed is that everything about the car screamed class. Sumptuous figure-hugging leather seats and door panels were the order of the day, while leather covered just about every other interior surface.

What little plastics there were on show were also top notch, as were the switches, audio controls and display dials.

As for safety and comfort, the Beemer came lavishly equipped. Dynamic stability control and front and side airbags help protect occupants, while adaptive suspension, including electronically-controlled dampers which lowers the ride height, offered the choice of either a sporty or a more relaxed driving mode.

And the boot of the BMW is large enough to stow a set of golf clubs ... or two if you find a model with the optional through-loading system between the seats.

Expect to pay between £14,875 and £19,970 for a 2010, 10-plate version and between £17,145 and £22,415 for a one year newer 2011 11-plate model, something of a bargain considering today's new price is in excess of £44,000.

However, a less powerful 23i sDrive version might appeal more, with a 2010 10-plate costing anything from £9,610 to £12,905.