Looking out of the window one grey and wet October morning, it's hard to understand why Brits buy more convertibles than any other country in Europe.

Our quick take

The BMW Z4 is one of those cars that some will harshly categorise as a "hairdresser's" car. It's a generalisation, applied to the likes of Audi's TT and Mercedes's SLK too. Yet it's one we find unfair and we suspect applied by people who've never spent any time in these cars. We've driven variants of each, and always come away impressed - and surprised - that they seem much better than their reputation suggests.

The latest updates to the Z4 - tweaks to the materials and trim, the addition of BMW's beautiful corona ring lamps - and the availability of this new, base level engine, only add to its appeal. When the top is down, it's early morning and the sun's coming up we can assure you, you'll not care less about any hairdresser jibes.

It may not be the most arresting car to drive, but it covers most of the important bases and most importantly, feels pretty special most of the time. And while we love our fabric roof roadsters, we can't deny that the Z4's folding hard top shape looks good either up or down, while the roof offers the ability to have a coupe one minute, open-car the next. Better still, as we found out in the first 340 miles of driving, if you tick a couple of important options boxes then you don't have to be of a remotely hardy demeanour to enjoy top-down motoring in the Z4 all year round.

BMW Z4 sDrive 18i Roadster - 4.0 / 5

Perhaps that's because there are now a wide array of cars - like the upgraded BMW Z4 as tested here - that feature a folding hard top, which in theory offers you the best of both worlds: it's a closed coupe when the weather's doing its typical British Bank Holiday thing, and an open-top when the sun has his hat on.

While testing a convertible in October might seem like a contrary thing to do, here at Pocket-Lint we like to put things through what we call a "proper" review. We don't do everything in the rain, but the BMW Z4 with a bit of the wet stuff was an ironic must, wasn't it?

We wanted to find out two things: did the Z4 annoy us by misting up, leaking or being hard to see out of on the day-to-day grind and commute? And second, just for how much of the time during our week-long test with it could we actually manage to keep the roof down?

An important box ticking exercise

We specifically set out to test the most basic of the refreshed Z4 range. The sDrive 18i is a new addition, and in BMW's new and slightly confusing naming policy, sDrive refers to its being rear-wheel drive. The "18i" - there to imply that it's a 1.8 litre engine - in fact means you get BMW's new 2.0 litre, four-cylinder turbo unit. It's in essence the same engine that's in the 20i and 28i models - but here in its lowest state of tune, with 156 horsepower. A little baffling, but there you have it.

The 27hp you forfeit in the 18i compared to the 20i equates to a useful saving of £2,100 on the list price. And given we don't think cars like this are typically bought by the kind of person looking for the performance of an M3, we've got an inkling that your Z4 motoring might best be sampled in the simplest, lowest-power form, complete with an asking price of £27,610.

If you're on a budget but want to make the most of your roadster, you'll need that £2,100 saving - and then some - for the more important options. In our view, the most critical of these to add are the Comfort Package, priced at £1,495, that includes a wind deflector and storage compartment pack, and the heated seats for an extra £295.

Without these add-ons, we couldn't really say how often you'd choose to stow the hard top. But with them, we can tell you that you can make the seat base roasting hot, crank up the heater temperature, don a hat and then still feel perfectly comfortable, warm, and able to listen to the radio with the roof off at motorway speeds in a cool British autumn.

Indeed so impressively refined and warm was the Z4's cabin, that we managed 340 of 400 miles with the roof stowed. On a week when the average temperature was 11C that's not bad going. That and, of course, we're the hard nuts of the tech world, clearly.

Singing in the rain

It's also interesting to note that the Z4's aerodynamics are such that you can drive through moderately heavy rain, with the wipers on constant, and - so long as you're doing more than about 40mph - you and the cabin don't really get wet. Yes, that was us driving through a rain shower on the M1, at 6am last Tuesday. We got some funny looks. But we were having a ball.

Keep a hoodie and a hat in the car - although we're not entirely sure that's the assumed clientele of most Z4 buyers - and we suspect if you're bloody-minded you could drive this car with the hood down most days of the year. So long as you don't park it up and forget.

Inside it's far from a bad place to be too. The roll hoops that rise up behind the seat backs are split by the wind deflector and the windows form a barrier such that you feel very protected and snug once you're down in the seat. Meanwhile, the gauges - a model of typical BMW clarity and washed at night in the gentle-on-the-eye signature orange - are deeply recessed under binnacle hoods. This means you don't get reflections or the inability to see what's going on in bright sunlight, which is not the case in some other cars we could mention.

And that Comfort Package option gives you a nice little array of nets, fold-out bins and arm rest slots which we found swallowed wallets, phones, peripheral cables, water bottles and even an apple - the edible kind, not a phone or tablet - all at the same time.

You sit low too, you feel like you're in a proper sports car - even if the Z4 technically borrows bits from other BMW motors like the 3-Series and isn't what you might view as a bespoke roadster like an Lotus Elise or Mazda MX-5.

READ: Lotus Elise S review

An everyday roadster. Or coupe?

No, being a true, old-fashioned style roadster is not the Z4's remit. It's a car to do the day-to-day in like a BMW saloon, and then fold the top back and get some fresh air wherever you can. And on this promise it delivers.

The cabin truly is as hushed and well trimmed as a fixed-roof coupe with the roof up. Our first test of it was passed with flying colours: it didn't leak, mist up or generally prove a pain to drive to work and back.

We've only two gripes. The first is the positioning of the iDrive controller, which is different from other BMWs and located behind the gearstick. This means that it feels slightly unnatural in use due to reaching backfire it. But more irritatingly, it meant we kept inadvertently pressing the rotary control knob when we were changing gear. Sorry if we inadvertently rang you last week. Otherwise, the iDrive system - in Pro Media Nav format as optioned here for an extra £2,165 - remains as impressive and largely foolproof as ever.

Then there's our second moan: that folding hard top performs a theatrical concertina dance when it stows or erects itself. And while it can be raised and lowered via the key button - which we like a lot - it does take its sweet time to fully stow and put itself back in place. A pain when a summer shower decides to catch you out in town.

The blame lies in the complexity of the several stacked bits of metal and glass involved. A fabric top shows its alternative benefit over the rigid bits employed here, by typically being much quicker to raise and fold away. But then it's not as refined when the roof up. Swings and roundabouts.

The ultimate driving machine? Not so much

Drop yourself low into the BMW Z4's driver's seat and you might expect a searing drive from a car that's not only a roadster - ergo, supposedly fun to drive - but a self-proclaimed ultimate driving machine typical of a BMW.

In the sDrive 18i, we've not got one of BMW's signature straight six engines. Instead it's one of the new breed of turbo-charged fours - started from cold it's clear that the exhaust has been tuned to deliver on the car's sporty promise by giving quite a pleasant little burble and certainly sounding much more engaging than the hushed start up of a 3-Series with this unit. But it's not a patch on a signature BMW straight six.

Still, while the least pokey in the range, this engine nonetheless doesn't feel slow if you're prepared to work it. A 0-60 time of 7.9 seconds is hardly to be sniffed at. It's just that you'll still be out-dragged by a 320d and both the 20i and 28i versions of this engine, which feature more power, deliver the same CO2 and - so BMW claims - fuel economy. In theory you've really got to want to make that couple of grand saving for it to seem worth going for the base engine.

READ: BMW 320D Efficient Dynamics review

Nonetheless, we were impressed by the powertrain - the engine and manual gearbox it was mated with suit the car. And we got about 34mpg when driving relatively hard.

So what's not to like, we here you cry? Well, the problem is that the Z4's suspension can feel a little all at sea on the road. The ride's constantly busy. And the suspension set-up appears to have quite a stiff front end, but then a relatively soft rear.

Combine this with the fact that you're sitting very far back in the car and driving the Z4 can take some getting used to. It's not bad, but at first you find yourself attacking bends in two bites when going for it. And the way the car loads up and communicates what it's doing through the steering wheel - or, more to the point, doesn't - doesn't really inspire confidence to hustle it hard.

Is the latest BMW Z4 an ultimate driving machine? It feels less of one to us than, say, a 3-Series does. Which for a sports car might seem disappointing.

But let's put it in context: keep your effort below seven tenths, drop the roof, and then the Z4's an enjoyable place to be, feels special in its own way and isn't bad to drive per se. Just don't expect it to up its game as happily as other cars in BMW's range when you're truly in a hurry.

To recap

BMW freshens up the Z4 and adds a base level engine that’s not without appeal – just a shame you don’t get better CO2 and fuel economy into the bargain. Otherwise the Z4’s appeal remains undimmed, with a snug cabin roof down, as good as a coupe roof up and a decent tech spec. Only slightly at-sea suspension settings when you’re really going for it let the car down.