Torque is what you get when you, for example, tug on the handle of a wrench to tighten or loosen a nut. Doing so exerts a twisting force still expressed here, in Ye Olde English, in lb-ft, as nobody on this side of the Atlantic has any idea what a newton-metre is.
Torque in an engine is generated by burning a fuel/air mixture in a cylinder, with the pressure of the expanding gases pushing the piston, which is linked to the crankshaft by a connecting rod, downwards.
As this occurs, the angle generated by the crankshaft "throw" increases and the rod, like the wrench handle above, rotates the crank. And that, with a few things such as clutches and transmission gears in between, is what makes your car move.
The Jetta TDI, with its turbocharged diesel engine, does this with a degree of vigour, accompanied by a high degree of overall flexibility not normally experienced in the compact-car category. Most small-displacement gasoline engines don't produce a lot of torque, and what they do is generated at higher engine speeds.
The TDI's four-cylinder engine delivers a disproportionate (for its displacement) amount of low rpm "grunt" that lets it charge off the line like a V-6 but also maintains that strong pulling power at highway speeds.
This allows it to coast along at minimal revs in top gear while sipping fuel at such a frugal rate that 1,000 km per tank wouldn't be an unlikely achievement. In fact, the number on the trip computer that estimates how much distance I had before needing more gas disconcertingly went up for the first hundred kilometres or so that I drove the car.
The TDI's arrival last year marked the return of the popular diesel engine option to the VW lineup in North America � it hadn't been able to sell a diesel here in 2007 due to U.S. emission standards � and the Jetta range now offers three engine choices, each of which gives the car a different driving character.
There's a gasoline-fuelled, 2.5-litre, four-cylinder that makes 177 hp at 5,700 rpm and 177 lb-ft of torque peaking at 4,250 rpm. With six-speed automatic transmission, it delivers very good performance and fuel economy ratings of 10.5 L/100 km city and 7.2 highway.
Also available is a performance-oriented, gas-burning, turbocharged 2.0-litre unit rated at 200 hp at 5,100 rpm and 207 lb-ft of torque from 1,700-5,000 rpm. This makes the 2.0 TSI Jetta a very quick car indeed and, thanks to the turbo, produces plenty of torque over that wide rpm range, which helps it garner very good fuel economy ratings of 9.0 city and 6.8 highway.
The 2.0-litre, four-cylinder diesel engine in the TDI delivers the least power, 140 hp at 4,000 rpm, but the most torque, 236 lb-ft, all of which is available from 1,750 to 2,500 rpm. Its fuel economy ratings are 6.8 city and 4.9 highway. The on-board readout was showing an average of 7.1 L/100 km when I returned it.
The "oil burner" appellation used above is in reference to the bad old days of low-powered and stinky diesel engines. This new one makes 40 hp more than the previous 1.9-litre unit and burns ultra-low-sulphur diesel very efficiently and cleanly and is also quieter.
And the direct shift gearbox (DSG) is a treat, snapping off lightning-quick shifts automatically or allowing you to select gears yourself. Although it takes a while to get used to the fact that it only revs to about 4,500 rpm between the gears, acceleration is surprisingly strong.
And its direct steering, firm suspension and good brakes also contribute to making it a very enjoyable car to drive.
The Jetta TDI is available in base manual transmission Trendline form at $24,275, in Comfortline trim at $26,775 and Highline versions go for $29,775. Our DSG-transmission-equipped tester had a sticker price of $31,175 and an all-in-but-the-taxes cost of $33,510. By comparison, a base gasoline Jetta 2.5 goes for $21,975 and a base 2.0 TSI for $27,475.
The base TDI comes with the usual features at this price, plus cruise control, climate control, 16-inch wheels, exterior temp gauge, a single CD audio system and front, side and side-curtain airbag systems.
The Comfortline has some extra chrome trim, a power-reclining driver's seat, heated seats, leather-wrapped wheel and a premium six-disc audio system. The Highline adds a compass, leather upholstery, a multi-function wheel, a sunroof and a rear armrest/pass-through.
In typical VW fashion, the interior is designed to meet more utilitarian than utopian standards for style. There's rather-uninspired plastic aplenty, not only where you can see it but also feel it � the surprisingly nasty and hard-edged door pull, for example.
The somewhat stark look and feel is ameliorated by stitched padding on the armrests, rather-nice mesh-finish aluminum trim and thin aluminum bezels around the gauges that perk up the plainness a bit.
The cabin is quiet enough at highway speeds, the leather-clad front seats are supportive and comfortable, the rear seat will handle two in comfort, headroom is good front and rear and the trunk capacity is fine at 400 litres.
In fact, if I had to cover a lot of mileage on an annual basis, I'd be happy to do it in the TDI, and would likely save some money if I kept doing it long enough. But the potent 2.0 TSI turbo's fuel economy numbers are pretty good, too, and it would still be my choice among the Jetta triad.
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