TAKING a gas-axe to the roof of a hatch or coupe can leave enthusiast drivers with an axe to grind, given that weight and wobbliness are often added, and performance and dynamics subtracted.

For this new Mini Convertible that now wears the John Cooper Works (JCW) racing nameplate, that may especially be the case given the tough-chassis reputation preceding models with those three letters, increasing the potential to shake the windscreen header rail right off its A-pillar mounts.

On the flipside – but not necessarily upside – this third-generation new JCW has traded some of the previous models’ raw aggression for a more rounded personality.

Settle into the bucket front seats of the Mini JCW Convertible and the soft-touch dashboard plastics, soft mood lighting, and superb 8.8-inch screen are in another league to previous models that were seemingly inspired by a Toys ‘R’ Us catalogue.

Everything feels semi-premium inside, although the lack of standard heated front seats is a cold move for a model that can go topless in wintry months.

Likewise, the extra-cost leather trim, keyless auto-entry and forward collision alert, all of which can leave the pricetag starting with a ‘6’.

Rear seating is a typical garden gnome-only affair, with the usual upright backrest, while folding the roof reduces boot volume behind the flip-down tailgate from a small 260 litres to a tiny 160L.

It is speaking loosely to say the roof goes down in the JCW Convertible, however. Rather it goes back and folds onto the rear decklid, and when it does the driver will find the rear-view mirror is virtually redundant.

Such pluses and minuses are shared with the regular Mini Convertible models that range from $37,900 (three-cylinder turbo) to $45,500 (four-cylinder turbo S). For the extra near-$10K over the latter model, the JCW raises power and torque of the shared 2.0-litre from 141kW to 170kW, and from 280Nm to 320Nm.

Look closely and note the 1320kg kerb weight of the JCW Convertible is 105kg heavier the JCW Hatch, leaving the 0-100km/h performance claim at 6.5 seconds with the standard six-speed automatic – just two-tenths faster than a significantly cheaper $39,900 three-door S auto.

Unsurprisingly the JCW feels more like an S on the road, though similar could be said (but to a lesser degree) for the extremely polished JCW Hatch.

The rawness and alertness of old has mostly vanished, replaced firstly by softer on-centre steering that then moves in a tight and progressive fashion.

As a child of the BMW Group, there are multiple modes to consider, and in the case of the steering that means dainty Normal or dull, weighty Sport.

Adaptive suspension is standard on the JCW – although fixed sports suspension is a no-cost option – and despite 40-aspect 18-inch run-flat tyres, there is excellent comfort in the default Normal and only slight jitteriness but with excellent body control in Sport.

Even large bumps fail to elicit major shake in the chassis, leaving this Mini Convertible to do a mostly convincing impression of a Mini Hatch. With the roof up there is noticeable road noise, and a rear rattle in the case of two of the test cars at the national media launch, but refinement is generally more than acceptable.

Delivering sharp throttle response with either the intelligent automatic or slightly rubbery and notchy manual – we sampled both transmissions – the turbocharged four-cylinder petrol engine shifts the JCW Convertible in a brisk, rather than speedy, fashion.

It never feels heavy on its feet, but 170kW/320Nm from a 2.0-litre turbo is below average by today’s standards and is a deliberate move by Mini to hold the engine back for later updates and/or more expensive editions. Essentially the same engine in a BMW 330i makes 185kW/350Nm.

The decision somewhat prevents this flagship Mini Convertible from feeling like a proper JCW.

Another very un-JCW decision is to fit Pirelli Cinturato P7 touring tyres (although Mini hinted that other types could be available). Already the chassis of this third-generation model has traded sharpness for stability, but the soft compound tyres do little to aid the adept chassis underneath.

The result is greater initial understeer than expected, while lift-off oversteer is beyond the ability of its generic dynamic repertoire. Poised and planted behaviour at modest cornering speed will be major upsides for many buyers, though, and can be fun, while the stability control is well calibrated.

Feed in staccato pops – but not crackles – from the standard sports exhaust on overrun, and the new Mini JCW Convertible could perhaps be an even more charming proposition than its hard-top stablemate. Then again, it probably adds little to the experience over the $15K-cheaper Cooper S – just add the optional sunroof if need be.

Any new generation bodystyle of S or JCW is overwhelmingly more convincing than older models, from the quality cabin, increased technology, smoother ride and faster performance.

The exception, however, is ultimate fun and character. A fast Mini used to have its own pin-pointy and go-kart darty personality that was like no other hot hatchback, but this latest JCW conforms to the agenda of polished mainstream rivals. It is just lucky the JCW Convertible has so few of them.