Driver's Seat: BMW M4 convertible comfortable, but fun takes some effort.

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The impressive BMW M4 Convertible is almost too smooth for its own good at top speeds.

2015 Chevrolet Corvette Stingray Convertible Z51 vs. 2015 BMW M4 Convertible: Price up, top down.

This week: 2015 BMW M4 Convertible.

Price: $96,075. A base starts at a much more reasonable $72,500; I'll expand on add-ons later.

Marketer's pitch: "M. The most powerful letter in the world."

Conventional wisdom: Oooo. Aaaah. BMW.

Reality: Open-road roominess. The fun is there, too, but can be hard to find.

Up to speed: Last week we toured the region in a Corvette, which offered speed and unbridled fun in the sun for two.

Two, two, two cars in one: Take the BMW out for a spin without overdoing it, and you're treated to a car that out-Cadillacs Cadillac. Here's a roomy luxurious ride, smooth and supple all around.

Spread out in the sun: One place the M4 wins is in seating. Every occupant in the four-seater convertible thought that the car was roomy and comfortable. The seats were covered in supple Sakhir orange/black full leather coverings for a mere $2,550, and I'm sure even the cow that once wore them feels honored.

What's new: The BMW M4 engine shrinks a bit for the 2015 model, back to a 3.0-liter inline six, where formerly the company used eight cylinders.

Super fast: The TwinPower Turbo engine creates 425 horsepower. That's a whole bunch of horses, and rockets the car to 60 in 3.9 seconds, but it's packed with so much smoothness that it took a while for me to feel that I was having fun.

On the road: The handling is clear and competent, but that feeling of zip or zig I got from the Corvette or a Jaguar F-Type (or even from Audis and other BMWs) was decidedly absent.

Exhaust note: A key ingredient for my driving pleasure is an engine that creates a symphony of cylinders. The M4 offers some noise after it's warmed up in the right mode, but I never fell in love with the sound.

Painful sum: Having to brutalize the engine while not feeling a sense of fun at normal speeds almost dares drivers to overdo it. Speeds of 80 and beyond are far too easy to reach and the M4 is so obligingly calm that the phrase "Officer, I truly had no idea" becomes believable.

Shifty: The $2,900 double-clutch transmission seems to be more trouble than it's worth. It shifts harshly like a stick without a clutch pedal, and is needlessly complicated to operate. A stick is available and slows that 0-to-60 by 0.2 seconds.

Hot seat: Did you know that you can buy a car for close to $100 grand and still suffer from a sweaty back when you arrive at work?

That's right; for $96,075, the M4 I tested did not come with cooled seats. For that price, I can get four of the Lovely Mrs. Passenger Seat's Kia Souls with cooled seats and a panoramic sunroof.

I think BMW should send along a protégé for four years or 50,000 miles to fan the backs of owners.

Let the sun shine in: Like the Corvette, the M4 top requires operators to keep the button raised or lowered during the entire process. The M4's hardtop moved much more smoothly than the Corvette's soft top, and as a hardtop let in scant little outside noise when it was up.

Fuel economy: I was averaging 23 m.p.g. on mainly highways, but it slid down to 21 after a few country-road tours. Feed the M4 premium.

Where it's built: Regensburg, Germany.

How it's built: Consumer Reports isn't buying a near-$100,000 car to test (no surprise) so no reliability data are available. The popular 3 Series is made at the same plant and it ranges from below average to average reliability.

In the end: Though both offer convertible fun without a budget, similarities end there. If you need a comfortable four-person unit, the BMW will fit the bill without complaint. But if you're just out for some fun, the Corvette satisfies.


ssturgis@phillynews.com215-854-2558