Unless you???re a serious performance junkie, torsional rigidity may not be something that???s kept you awake at night. A modicum of flex in a vehicle???s structure doesn???t hurt, but overall, you don???t want too much torsion in your car???s body. Why not? Low rigidity results in vibrations and degrades handling performance. A decent handling car relies, to a greater extent than many realise, on suspension designs that optimise tyre and road contact under all conditions. Introduce too much torsion into the equation and the maths gets tricky really quickly. In short, the wheels are no longer where they are supposed to be relative to each other. In these cases, even well-engineered suspensions don???t stand a chance. This problem tends to affect cars that have been cheaply converted into drop tops. Cars that were designed from virtually a clean sheet of paper to be convertibles usually have the right amount of torsional strength built into their chassis. Cars like the Vauxhall Astra TwinTop for example. Drive the TwinTop 2.0T and you???ll feel a little more flex than in its hatchback sibling but not much. Drop a wheel deliberately into a pothole and you???ll feel a little kick in the steering and spot the rear view mirror vibrate momentarily before composure is regained. It???s an impressive showing for a car with its roof in the boot. What???s more, this model encourages enthusiastic driving. No, it???s not going to give the VXR hatch a run for its money on a hillclimb route, but the 2.0T model is plenty quick enough to entertain, getting to 60mph in a vanishing 8.3 seconds and running on to a top speed of 146mph. You???ll want to put the roof up for that sort of endeavour though. It???s one of the better engines that Vauxhall produce and, for what it???s worth, I think it???s a more impressive engine than the one that powers the VXR hatch - a car that feels as if it???s got a few too many ponies for its own good under the bonnet. With 197bhp on tap and a relatively lag-free turbo installation, the 2.0T unit is tractable, reasonably melodic and built like a tank. Blow one of these things up and you probably merit some sort of award.

Priced at ??20,740 on the road, the 2.0T isn???t pocket change but compares favourably with cars like the entry-level Volvo C70 coupe-cabriolet which runs around ??5,000 more and is down on power as well. Only one trim level is offered, Design, although this comes with all manner of goodies including 17-inch 10-spoke alloys and a sports steering wheel as well as other styling features to add a dynamic edge. Rain-sensitive windscreen wipers, an anti-dazzle rear view mirror, automatic lighting control and a windbreak are also all standard. There???s even an automatic pop-up roll-over protection bar, making the lines even sleeker without compromising safety. The TwinTop has some great genetics to back it up. The old Astra Convertible may have relied on a relatively low tech fabric roof, but a combination of sleek Bertone styling, a range of surprisingly punchy engines and some very attractive pricing ensured that it was a big seller. It may not have been the sharpest drive but it was blatantly populist and curiously endearing. The Astra TwinTop moves the game on by offering a folding roof that???s composed of three main sections instead of the usual two piece affair. This means that you don???t need to fold two huge pieces of metal into the car???s rear end, avoiding the strangely misshapen looks of some coupe-cabriolets. At the press of a dash-mounted button, the two overhead sections of the roof stack on top of the glass rear window and hinge backwards into the boot, offering the usual benefits of added security and safety of a hard topped car with the wind in the hair feel of a convertible. What???s more, the Astra TwinTop isn???t merely an Astra hatch that???s had an angle grinder taken to it. As we???ve already explained, the body was designed from the ground up as a convertible and Vauxhall reckon the two cars share at most 30 per cent of their body parts. With excellent chassis rigidity when the roof is in place, driving dynamics approach those of the lauded Astra hatch. Designed at GM Design Europe in Germany, the Astra TwinTop goes into battle against the likes of the Peugeot 307 CC and Renault Megane CC although at almost 4,500mm in length, it???s usefully bigger than both of these French rivals. The styling is also better resolved thanks in no small part to that clever folding roof arrangement. The rear end carries over the petal-shaped lights of the Tigra and luggage space is better than you might expect, even with the roof stowed. Utility is enhanced by 'Easy Load', a feature raising the horizontally stacked parts of a folded roof at the push of a button, making cargo easily accessible. Great when you???ve got an armful of shopping in other words. How well this car does relies on how customers perceive its value proposition against the Ford Focus coupe cabriolet and Volkswagen Eos. With the far slower 2.0-litre FSI version of the Eos costing more than the turbocharged Astra, it???s fair to say the Vauxhall has the VW???s measure but the Ford is a tougher rival. Grab a seat and tuck into your popcorn. This one could get interesting.