WHEN you consider that one of Saab's top-selling models and one of Australia's most popular cabriolets, the 9-3 Convertible, is priced from $65,500, and that BMW's $12,000-cheaper new 1 Series Convertible has no direct rival in the German maker's own open-topped model line-up, it's easy to see why the company has high hopes for its first compact luxury drop-top in more than three decades.

Throw in all the traditional BMW hallmarks like a rear-drive layout (which the 1 Series Convertible is alone in offering in the class), near-50/50 weight distribution and no shortage of performance across the three-engine range, and it's no wonder BMW predicts it will sell more 1 Series Convertibles than 1 Series Coupes – and that most buyers will be new to the BMW brand.

Unlike many of its luxury convertible rivals, the latest BMW soft-top offers both style and substance. BMW says its chassis is as stiff as the 1 Series Coupe upon which it's based and after a full day of driving on testing Adelaide Hills roads, we have no reason to doubt that.

In fact, with a generally softer suspension set-up than both its coupe and hatchback siblings, the open-topped 1 Series not only delivers the sort of steering precision and feedback and chassis agility and balance for which BMW is famous, but combines a level of ride comfort that its fixed-roof stablemates can't match – despite the fitment of run-flat tyres.

Of course, the packaging compromises wrought by the 1 Series' rear-drive layout are less of an issue in the style-concious convertible market, but BMW's smallest soft-top still offers enough space for its two rear passengers and a boot that becomes smaller than class-average only when the roof is stowed. Rear-seat legroom can get cramped when a full-sized passenger sits up front, however.

Front-seat occupants also miss out on the 3 Series coupe and convertible's automatic seatbelt feeder system, but the 1 Convertible's shorter doors mean it's not too much of stretch to reach them anyway. And with the windows up, a surprising lack of wind noise and buffeting means passengers can converse comfortably at speeds of up to 120km/h – even without the standard wind blocker in place.

The fully automatic roof system works quietly and seamlessly in a relatively slow 22 seconds and, as with most convertibles, reduces rear three-quarter vision significantly. Rear-vision through the heated glass rear screen is acceptable, however, and the soft-top stows nicely underneath a well-integrated, flat rear deck and, like the Astra, can be operated at speeds of up to 40km/h.

Concealed pop-up rear rollover hoops are also exclusive to the 1 Series Convertible, which offers other unique features like a dual-zone climate-control system with “convertible mode” and sun-reflective leather trim. There are also familiar 1 Series features like sizeable door storage bins, cruise control, a full-function trip computer and the fiddly, two-stage start/stop button.

While the 2.0-litre four-cylinder engined 120i lacks the eagerness and familiar metallic sound of its six-cylinder brethren, it should certainly be perky enough for most convertible buyers – even if its fuel consumption appraches that of the 125i in silky-smooth six-speed auto guise, which offers handy steering wheel shift paddles on six-cylinder variants but further dulls the 120i's performance.

We spent most of the day in a slick-shifting manual 125i, which didn't feel 80kg heavier than the 120i because of its more muscular power delivery which necessitated fewer gearchanges.

Its broad, linear power output is a good match for the 1 Series Convertible's taut chassis, but still felt a little lacking at engine speeds under 3000rpm. But the characteristic BMW exhaust crackle was still evident when the throttle snaps shut.

The same is unlikely to be said for the white-hot twin-turbocharged 335i, which like the 120i and 125i is available in both six-speed manual and auto guises but is also lower and firmer, but unfortunately didn't arrive in time for last week's media launch.

We doubt the 100kg-odd increase in weight over the brilliantly rewarding 335i Coupe will noticeably blunt the roofless car's 225kW and 400Nm performance figures, and it's a credit to the car's body reinforcement that a small convertible can so readily handle the potential of such a high-performance engine.

'Our' 125i Convertible returned a respectable sub-15L/100km fuel consumption figure after spending all day in the upper half of its rev-range, and the 335i Convertible's extra force-fed performance isn't likely to bring any more than the 0.7L/100km penalty claimed by BMW.

Fifty three thousand dollars may not be chicken feed and the 125i and 135i Convertible are no bargains at $63,000-plus and $78,000-plus respectively. In fact, the latter two prices represent a tidy $9000 and $7000 premium over the 125i and 135i Coupe respectively.

But with plenty of performance from all three engines, wrapped in a stylish and rigid rear-drive chassis that handles like a true BMW should and rides even better, the 1 Series Convertible easily has what it takes to sway many buyers away from popular front-drive coupe-convertibles like Volkswagen's Eos and Holden's Astra TwinTop.