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As a youngster, I was obsessed with power-to-weight ratios and the closely related acceleration figures: They were so definitive descriptive af a sporty car. 40 years later I realized they can be quite meaningless.

This dawned upon me one beautiful morning behind the wheel of my Jaguar XJ12 (only very recently acquired and the process and thoughts behind that – as well as the car itself – was presented in the article My first Jaguar: XJ12 Sovereign) as I turned a corner in the almost two tonnes of super saloon. Everything about the big Jaguar is just so effortless. It’s amazing really, and rather difficult to grasp just how the boys at Jaguar actually managed this feat.

The 5.3 litre V12 under this bonnet is not only a magnificently quiet and smooth engine – it also makes the XJ12 quite a rapid machine.

As I turned the corner from standstill and depressed the accelerator, all that weight was apparantly gone – but this is actually much easier to understand: The 5.3 litre V12 delivers a mighty 432 Newtonmeter (that’s 319 ft-lb for you non-metrics out there) against the weight, and despite being limited by a threespeed automatic ‘box of the older era, the car gains speed with an equally effortless attitude.

In fact, “effortless” is perhaps not quite the word if you truly bury the right pedal (and regarding the wording, please note that you can not, in an XJ12, call this pedal “the loud pedal”, as the V12 never releases much more than a slight murmur even when stomped on), as the XJ12 was regarded as as seriously fast car. In its early years as no less than the fastest saloon in the world – and although by 1987 the game had moved on, the XJ12 was still no slouch.

How fast is it then? Well, should you for some odd reason decide to put the XJ12 on a quartermile strip, it would turn out a time of 15.8 seconds and cross the line with a speed of 146 km/h. As I’ve never done that (and probably never will either) those numbers are pretty abstract to me. But let me nonetheless compare them to my Alpine Renault A310, which is of course a much more sporty car. Well, a proper sports car, even. My Alpine would cover the same quartermile in 15.5 seconds and cross the line with a speed of 147 km/h. Keep your foot thoroughly planted for a full mile in both cars and they would cross the line side-by-side in an identical 28.3 seconds.

The driving experience in the Alpine could barely be any further removed from that of the Jaguar – yet the two turn out almost identical performance numbers.

That’s amazing, isn’t it? The reason is of course to be found in the power-to-weight ratio: In the Jaguar every horsepower has to haul 6.5 kilos; in the Alpine it is more at 6.8 kilos. Ahh yes, the power of power: 295 horsepower against the Frenchman’s 150 yields those numbers.

Mind, in those aforementioned youngster years, I would have still triumphantly exclaimed “Yes, the sports car IS the faster” and pointed to the clear advantage of .3 of a second. Nowadays, I understand that it would actually demand some seriously heavyhanded use of the cluth as well as perfectly timed and executed gearshifts to manage those times in the Alpine – while the Jaguar would merely require a heavy foot to depress the pedal deep into the thick pile carpet. In the real world, the big cat would probably turn out faster a lot of the times. Top speed? It could barely be more irrelevant – but in case you’re wondering: The Jag would continue to 233 km/h where the Alpine would top out at 225.

Jaguar XJ-material doesn’t make much fuss about performance as such: The car is not really about that.

Thing is though – those numbers are not an important aspect anyway. Sure, the numbers may be very similar but almost nothing else is – and certainly not the way these two cars deliver those numbers. THAT is the important thing: The Jaguar and the Alpine represent two totally different approaches towards performance. Or rather towards building a car as such. In fact, I think one could even say that the performance of the Jaguar is actually more a by-product of the effortlessness which the development team pursued. Of course you’re not doing quartermiles in an XJ12; you’re wafting. But in order to waft with proper disdain for inclines, the elements and loads, you need a surplus of power. The XJ12 has just that!

The Alpine is much more a matter of efficiency: It delivers the same numbers with only half the power, as it is a sports car bred for performance. But even the A310 isn’t really about straight line acceleration and topspeed anyway. As a true sports car, it really comes alive in the corners which is where it shines like few others. I have no doubt whatsoever that it would leave the Jaguar behind on a track – but even the mere thought of actually attempting such a comparison of lap times is completely perverted and would be every bit as irrelevant as acceleration figures.

For me, the Alpine is more about the driving.

My point here is that numbers can never tell the complete story. In fact, I am sure that they can even tell the wrong story: I don’t think I’ve ever driven a car so refined, accomplished and utterly superior as the XJ12! Yet the numbers don’t portray this in any way. In short: You should not buy an XJ12 for its grand numbers – but much rather for enjoying its grandness when you drive it.

3 Responses

  1. Tony Wawryk

    Nail hit firmly on head, Claus. While numbers make all the difference in a game of Top Trumps, on the road it’s surely always been about how power is delivered and the manner in which a car does what it does.
    It’s why enthusiastic drivers love the lightness and handling of, for example, a Lotus 7 (or indeed a Europa or Elan) – the power-to-weight ratio of these cars is just part of the story. These cars might well be more fun on a country road, but for Autobahn cruising, I’d much rather be in your Jaguar. These are two extremes in terms of, well, almost everything, but you could pick many more examples (including yours) that illustrate the point.
    We used to have an Audi Avant 2.0 TDi as the family workhorse (I can hear the cries of derision from here) and let me tell you, as a motorway cruiser, it was superb, and thanks to the way it delivered it’s relatively ordinary 140bhp, it accelerated very nicely once on the move, thank you. Was it much fun? Of course not, but that wasn’t it’s point.
    You used the word “wafting” – perfect, as Jaguar saloon drivers bought their cars not to hurl them around corners (except when used as getaway cars), but for the “Grace, Space and Pace” they were promised. And that was the point.

  2. Claus Ebberfeld

    Thanks, @tony-wawryk . Maybe I should mention that as a youngster I was also obsessed with lightweight cars, Lotus in particular. I hope to get to that at a later stage…would also be a nice antidote to the XJ12!

  3. Anders Bilidt

    Just to ram Claus’s point home once and for all, I’ll just add to the discussion that what was possibly the most entertaining ride I’ve ever owned, had all of 55hp from a pewny 875cc engine. Needless to say, the little Sunbeam Imp Sport couldn’t brag about astonishing acceleration figures and even less so about galactic topspeeds. But hurl the tiny rear-engined Imp down a twisty lane or through a succession of roundabouts, and oh-my-god did it make me grin like a Cheshire cat… :-)
    Perhaps the only car I’ve owned which beat the Imp for smiles per mile was my Toyota Trueno 1600GT, which mustered all of 110hp from its 1.6-litre twincam. Granted, that’s exactly double the output of the Imp Sport, but in the grand scheme of things, it’s still a pretty humble figure.

    All of which is not at all to say that big engines with masses of power can’t be fun. Of course they can! But they just aren’t by default – at least not outside of the pub… ;-)


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