Would you buy a Land Rover sports car? What about a Porsche off-roader? Now think carefully. Sure, the Porsche Cayenne will be the worlds fastest and best handling 4X4. So what? The Sultans of Stuttgart will have answered a question no one asked: how do I get a truck to lap the Nurburgring faster than a Nissan Skyline GT-R? Here in the real world, the biggest question vexing MPV drivers is this: what time does Janie's football practice end? Considering the cataclysmic damage these lumbering behemoths inflict on lesser vehicles at a walking pace, the average MPV driver needs less speed, not more. Put Mum in a Porsche off-roader and it's only a matter of time before the entire soccer team is goading her to blow off the jerk in the Merc.

Safety aside (as always), the Cayenne will sell. Plenty of posh Porsche posers will love seeing their Cayenne and Carrera snuggling together in a darkened garage. I find the concept incestuous and redundant. Stick snow tires on a Carrera 4 and you've got a four-passenger car that makes normal sedans seem like Ice Capades rejects. The Cayenne adds elevation to the equation, but it also introduces mass. Drivers will be able to see into next week, but they'll constantly be out-handled by smaller, lighter machines. Still, as a capitalist cheerleader who once owned a TVR, I can hardly begrudge buyers a car they need like they need satellite-controlled headlights that swivel to follow the road. I'm more concerned about the Cayenne's effect on Porsche.

The Cayenne is a sign that Porsche is making too much money: £5385 per car. This phenomenal, seemingly unstoppable success has given Porsche Hitlerian hubris. OK, we've done Europe. Let's invade Russia! OK, we've done sports cars. Let's take on GM, Ford, Chrysler, Land Rover, Mercedes, BMW, Toyota and Mitsubishi! The fact that Porsche can't make enough Boxsters and Carreras to satisfy demand seems to have escaped the notice of their Bored of Directors. Lest they forget, the upcoming, V10-powered GT will put the company toe-to-toe with Ferrari's F60. With the Cayenne, Porsche doesn't blink so much as sneeze. Is this really the same company that agonised for years about making a four-door 928? It's as if they decided to apply their motor sport heritage to designing brief cases. Oh wait, they have.

The process of applying brand values to increasingly disparate products is called brand extension. Like hair extensions, you think you're getting something better. You're not. Mercedes, once proud producer of bank vaults on wheels, slaps its star on downmarket tat. The next thing you know they're making cars so nasty they're called Chryslers. And BMW's product range may lead the casual observer to believe that a carmaker can do it all, but I doubt they've ever tried to corner a Z3 on a greasy roundabout. Mercedes, BMW and Porsche will all learn that extending a brand damages your roots. Sooner or later, they'll all have the economic equivalent of a bad hair day.

A successful carmaker must have Focus. Just ask Ford. All their cars are sold on value for money. Maintaining this single-mindedness imposes natural limits on a brand's potential. Ford will never beat Bentley; value for money is not exactly the luxury car buyer's first concern. Similarly, you'll never see a fifty-acre field filled with pre-registered Bentleys. So what's the point of the Cayenne? It may add a zero Porsche's balance in the short term, but it's an evolutionary dead end. In the 4X4 market, Land Rover owns the high ground, where people still care whether a car can climb a tree (or at least looks as if it can). Ford and Chrysler own the low-road, where middle-class Moms have better things to spend their money on than an off-roader than can hurtle her brood down a highway at 155 miles per hour. The Cayenne will be smack bang in the middle, scrabbling for purchase in a tiny niche, forever fighting off Mercedes' ML and BMW X5.

Meanwhile, carmakers that focus all their efforts on creating machines that go like Hell will continue to thrive. As long as Peter Wheeler shovels massive grunt into lightweight bodies, there will be a TVR hovering around at the bottom of the J D Power survey. As long as Lotus makes cars that corner like roller coasters, TVR will have suitable company on that list. There will always be a hard core of wealthy enthusiasts who believe that driving "off-road" means one thing: they've lost control of their sports car. Every man-hour Porsche spends on the Cayenne—designing, marketing, servicing, etc.— is one man-hour less for maintaining and extending their dominance in the sports car market. In other words, the Cayenne is a waste of time.

At the end of the fiscal year, the best thing a world-class sports car maker like Porsche can make is… wait for it… sports cars! Porsche ignores common sense at its peril. Which reminds me; didn't Lamborghini once build a four-wheel drive thingy? Oh yes, now I remember: the LM02. It was an awesome beast, powered by a 420bhp V12. That was 1986, just before Lamborghini lost their independence. Again.

The new Range Rover is Top Gear's magazine's Car of the Year. Car? I'm sorry, but my definition of a 'car' doesn't include vehicles taller than six feet that weigh nearly two and a half tons. The Range Rover is, according to US environmental and safety regulations, a truck. Truck by name, truck by nature. No amount of ABS, traction control and terrain sensing suspension can alter The Laws of Physics: mountainous mass X V8 acceleration + slippery surface = endless understeer oblivion. As Top Gear's own writer put it, the Range Rover's quest for soft-road world domination will ultimately end 'in a ditch'.

Don't get me wrong; I'm sure the new Range Rover is a damn fine truck. Isn't it? I've yet to pilot the beast, but the few British journos who weren't busy singing 'Land Rover of Hope and Glory' at the truck's launch noticed a few 'glitches'. One version's adjustable air suspension got stuck in mid-air- a problem not unknown to owners of the previous model. One or two reviewers also didn't fail to notice the Ranger's prodigious thirst (12mpg), sloth (0 – 62 in 9.2 seconds) and square-rigged susceptibility to side winds. But hey, what do you expect? It's a truck. A truck that still hasn't released its Euro NCAP crash worthiness rating.

Aside from semantics, build quality, global warming, performance, handling and safety, my biggest problem with Top Gear's selection is that I can't understand their criteria. The magazine avoided the thorny issue of how a Range Rover is superior to a Lamborghini Murcielago (aside from the obvious fact that you can say 'Range Rover' without sounding effeminate) by simply leaving out the bit that explains how they made their choice. Well, TG does say the Range Rover has more 'all round excellence' than the luggage aversive Lambo. OK guys, but what makes the Range Rover more of an all-rounder than a BMW Five Series? The fact that it can drive to places where the rescue service arrives in a Toyota Landcruiser? I don't think so.

It's probably more a case of wishful thinking. TG's post-Empire unconscious must instinctively yearn for an English car that's a world-beater, even if it is a truck. Someone should tell TG that even nostalgia ain't what it used to be. I once took out a small village in a barely controllable, formerly all-conquering Jaguar XK120 (which may have been the car's intention, but not mine). Anyway, like the Royal family oneself, the Range Rover is a murky collection of British and German genetics. Even overlooking its BMW engine, I wonder if TG would have given Ford's latest truck the gong if it had been built in Detroit. Like, say, the similarly inoffensive Cadillac Escalade. Again, methinks not.

TG's editors should take the time to define excellence before they publicly announce it. Otherwise, they open themselves up to charges of misguided patriotism-or worse. (I once saw a vicious pub fight that started over the relative handling merits of a Nova vs. a Saxo. A Black Maria won.) If excellence equals technological innovation, anoraks will remind you that the new Range Rover's monocoque construction and air suspension predate the Defender. If excellence means drop-dead style, only a Multipla owner could deny that Mercedes' new SL is a more elegant evolution of a familiar form. And if excellence means bang for the buck, Scooby Doo, Landie don't.

To be fair, TG did a lot better in the semis. They recognized the Civic Type-R as an engineering masterpiece that costs only slightly more than the VAT on a Ferrari 456. They admitted that the Subaru Impreza Turbo is still the best- if most insect-like- driver's car ever unleashed on English roads. The plastic fantastic Renault Avantine earned a justifiable nod as the boldest new mainstream, um, thing. And who can [be bothered to] argue with their choice of the Nissan Primera as the best 'medium car'? They're all sane, safe choices for Best in Class. Porsche owners may howl with high-octane indignation at TG's conclusion that an Audi TT is better than a 911, but it's hard to share their outrage. After all, they have a 911 with which to console themselves.

I wish TG's final choice had been a little less NHS, and a lot more Pop Idol. A 'chalk or cheese?' people's poll would have been a far more equitable way to select an overall winner from such disparate machines. Perhaps it's a bit much to ask for democracy from a magazine spawned by a TV program on a channel funded by a mandatory tax on people's TV sets. So let's do it ourselves, through that newfangled thing called the Internet! Simply press the comment button below and nominate your own Pistonheads Car of The Year. Don't forget to include your justification. I'll start by nominating the BMW M5. It's the best car in Britain because I bought one. So there.