I’m making my wife sick. Not a new event, surely, but certainly the first time in a car. My normally impervious spouse is in the back seat of a BMW Alpina B7 luxury sedan and we’re on mile 11 of the most vertiginous, cutback roads I’ve ever encountered.

I should know better, but I can’t help myself, attacking corner after screeching corner. Even the leather-swathed back bucket seats aren’t enough to counteract the effects of heavy braking and constant swaying.

“Jason,” Miranda says, face paling. “Really?”

Probably not what she had in mind when I’d suggested a tour through Sonoma wine country in a spacious, sophisticated sedan. Yet my friend and front passenger, another Jason, lives in northern California and knows the best back roads. So maybe Miranda should have known better, too.

Not that this long-wheelbase model rides poorly. Anything but. After all, carmaker Alpina, in Buchloe, Germany, based it on my favorite executive haulers of all, the latest BMW 7 Series. It seems impossible that you could get carsick in one.

There’s a compliment lurking in there. I wouldn’t even attempt this type of death-defying, sports-car driving with any other luxury sedan. If I’d been in a Lexus LS or even a Mercedes-Benz S-Class, I would have stayed on littoral highways rather than cresting a coastal mountain range, slamming on the brakes, skirting a cliff without guard rails, and then sliding the back end around an uphill bend.

The regular, $86,000 750Li is like a Transformer robot which morphs from CEO swaddler to evil Megatron road scorcher with the twist of a dial. The $126,775 Alpina B7 has been revised and retuned so that it’s both faster and plusher, taking the duality even further.

In its home country, Alpina is classified as an official auto manufacturer, though it only works with BMW models. In the case of the B7, the extra $40,000 gets you greater power and more nuanced handling, extra leather and more than $10,000 worth of included options. Alpina differs from BMW’s inhouse tuning division, M GmbH, in that it focuses on adding luxury as well as greater performance. While the U.S. consumers can buy M models ranging from the hardcore M3 coupe to X6 M crossover, the only Alpina currently on offer in the States is the 2011-model year B7.

Alpina got its start in the 1960s when owner Burkard Bovensiepen transformed his father’s typewriter business in southern Germany into a sports-car tuner. It began working hand-in-glove with BMW, and today Alpina models are developed in tandem, and are both warranted and sold by BMW. Burkard’s sons, Andreas and Florian, now run the business.

Priced at $122,875 for the short wheelbase version and $126,775 for the long wheelbase, which is stretched 5.5 inches, the B7 is also available with all-wheel-drive.

Outwardly, it takes a devout Bimmer-head to notice the altered front fascia and rear end. While the word Alpina is embossed on the rear, the BMW badge remains. Most noticeable are the 21-inch wheels with Alpina’s gorgeous, distinctive 20-spoke rims.

The big difference is in the guts. The twin-turbo, 4.4-liter V-8 gets reinforced cylinder heads and bigger turbo chargers, as well as an improved cooling system to counteract the extra generated heat.

The result is significantly more torque: 516 pound-feet versus 450 in the 750Li. Extra horsepower comes your way too, with 100 more adding up to 500.

I subscribe to Alpina’s way of thinking that the torque is the most desirable type of additional power in a heavy sedan. From a standstill, the Alpina surges forward with a smooth and powerful gait.

Alpina says it concentrates on making the B7 both better riding than the 7 in comfort setting and more aggressive in the sport settings, the result of an electronically adjustable suspension that also inhibits body roll.

In the softer mode, the car feels like it rides on a carpet of air, almost to the point of being squishy. Even the car-sick prone could read “War and Peace” on the move and not feel queasy.

Switch the dial to “sport sharp,” and the B7’s lowered ride and sharper suspension suddenly leap to the fore, making it hotter and fiercer than the 750Li.

To my thinking, it’s nearly impossible to beat the cabin of the current 7 Series. Wisely, Alpina mostly stays out of the way, adding extra swathes of hand-stitched leather and some of its own badging. A better stereo, heated rear seats and a head-up display are included.

Our challenging road eventually peters to rough gravel before meeting up with Highway 1, itself one of the world’s most challenging and serpentine routes. My passengers still seem relieved.

I make a quick pit-stop at a roadside store and upon returning find that Miranda has moved up front. She points at me and then juts her thumb toward the back.

I open my mouth, then meekly climb in. Fair play. There are worse places to be stuck in.

2011 BMW Alpina B7

Transmission: Six-speed automatic

Speed: 0 to 60 in 4.5 seconds

Gas mileage per gallon: 15 city; 21 highway

Price as tested: $126,775

Engine: 4.4-liter twin-turbo V-8 with 500 horsepower and 516 pound-feet of torque