17/4/12

Overview: BMW Mini Roadster

You can’t accuse BMW of not getting the most from the Mini brand. Apart from the standard hatchback model, there are Clubman, Countryman and Coupé derivatives, each living in its own market niche with no obvious direct competitor. There is also the Convertible, which has been around for three years and offers open-top motoring for four, albeit with next to no luggage space.

When we say that the Minis have no direct competitors, we are not suggesting that they are somehow flawless, beyond the reach of other products. Far from it. The point is that it is not function but style and driver-appeal that sell the Mini range. They are all agreeable to drive, and they all suffer infuriating design quirks that their owners are more than happy to live with. They have ‘character’. Maybe a Fabia Combi is more accommodating than a Mini Clubman, but that’s missing the point. The Škoda’s not cool, is it? It also doesn’t drive like a sportscar, and in this respect BMW has the substance to go with the style. Minis might have their faults — not the least of which is their trendiness, some might say — but they are good to drive.

And so we come to the Roadster. A second soft-top Mini. Squeezing the pips a bit, isn’t it? Modular design and production engineering are wonderful things, but these two cars are — barring the platforms — not variants of the same thing. The structures and interiors are appreciably different: there is a lot of investment in engineering here.

Before we get cracking with a description of the Roadster, it’s worth commenting briefly on names. ‘Roadster’ was what British drivers called soft-top sportscars before such imported terms as Convertible (American) and Cabriolet (French) put in an appearance in the 1950s. It’s a harking-back to village-green Britishness. ‘Convertible’ and ‘Cabriolet’ historically referred to soft-top versions of cars that otherwise would have had proper roofs, often quite ordinary saloons. So BMW is being true to the etymology.

In the context of the Mini range, the Roadster is a two-seater while, as we mentioned, the Convertible has room for four (with a giant glove-box behind). A Roadster comes with a manually-operated roof and an almost-respectable 240l boot, while the Convertible uses an electro-hydraulic system that will work with the car moving at up to 30km/h. The Convertible’s boot-lid drops down, like the original Mini’s, to reveal a volume of either 125l or 170l, depending on whether the top is up or down. The seats do fold, though.

All variants of the Mini Roadster carry the Cooper name in their model titles. The three petrol engines are all derivatives of the 1598cc BMW-PSA power-plant, while the single diesel model takes the 1995cc all-alloy BMW engine familiar from 1-, 3- and 5-series BMWs.

The entry-level model, badged Cooper, uses an atmospheric version of the 1.6 petrol engine. Valve timing and lift are controlled using a version of BMW’s Valvetronic system. Headline outputs are 122PS at 6000rpm and 160Nm at 4250rpm — this is an engine that needs to be worked.

The Cooper S Roadster adds a twin-scroll turbocharger and direct injection. The exhaust ducts are combined into two pairs, with each pair delivering exhaust gas to one of the two primary turbines in the blower. This arrangement (says BMW) reduces exhaust back-pressure and improves response. The direct injection system’s multi-hole injectors are supplied with fuel by a two-piston high-pressure pump, with injection pressures up to 12MPa. Outputs peak at 184PS and 240Nm — the latter arriving at a convenient 1600rpm. An overboost function offers a brief 260Nm.

The third petrol model is the John Cooper Works Roadster. The engine is substantially modified compared with the Cooper S variant, and is not dissimilar to that used in the Mini Challenge Clubsport series. Maximum outputs are 211PS and 260Nm (or 280Nm with overboost).

We have always felt that the Cooper SD is the most enjoyable Mini to drive across country, for the simple reason that its torque allows you to maintain a cracking pace without much effort. Unlike the humbler Cooper D, the SD uses a ‘proper’ BMW engine — though we mean no offence to the excellent 1.6-litre PSA-Ford unit in the Cooper D, which does a splendid if less spectacular job. The Cooper SD engine features solenoid injectors and a variable-geometry single-scroll blower; peak outputs are 143PS and 305Nm.

All Roadster models bar the Works derivative feature a package of familiar energy-saving measures: kinetic energy capturing, automatic stop-start, electric power steering, a variable-displacement oil-pump controled by the engine map and on-demand ancillary operation. There’s also a gearchange indicator on the dash. All have a six-speed manual gearbox as standard, and all except the Works model can be had with a six-speed automatic which provides a considerably wider span of ratios and higher overall gearing. Shift paddles to go with the automatic box are an option. Curiously, the Cooper S and Cooper SD use identical gear ratios, despite their profoundly different engines.

A Sport button on the centre console — standard in the case of the Works Roadster and optional for all other models — allows the driver to adjust the car’s steering characteristics and accelerator responses. If the optional six-speed automatic gearbox is specified, pressing the Sport button also shortens shift times.

BMW boasts of the Roadster body-shell’s torsional rigidity, though figures are not available. Necessarily, the structure is reinforced to make up to some extent for the lack of B- and C-pillar hoops. The windscreen frame is described as ‘exceptionally rigid’: it, along with the hoops behind the seats, provides roll-over protection. Reinforcement is incorporated into the front and rear of the body and the sills. The structural alterations result in a slightly higher front axle load compared with the standard Mini; the use of a comparatively lightweight, manually operated soft-top roof lowers the car’s centre of gravity.

Running-gear is the usual very competent Mini fare. McPherson struts look after the front wheels, while the rears have a multi-link axle with aluminium longitudinal struts and centrally-pivoted control arms. The electric power-steeping is speed-sensitive. All models can be specified with sports suspension, which brings stiffer damper settings, sturdier anti-roll bars and upgraded springs. The standard Dynamic Stability Control system selectively brakes individual wheels and reduces engine power to limit under- or oversteer. The system includes anti-lock braking, Electronic Brakeforce Distribution, Cornering Brake Control, Brake Assist and Hill Start Assistant. DSC also adds Dynamic Traction Control with Electronic Differential Lock Control for the driven axle as standard on the Works Roadster and as an option on all other models.

As we mentioned earlier, the Roadster’s roof is manually operated. It is opened by turning the release lever on the windscreen frame though 130 degrees and swivelling the soft-top back behind the seats, where it locks into place. To close the roof again, you need to press a button between the roll-over bars, which allows the roof to extend out of its anchorage points. It can then be pulled forward, using a recessed grip and assisted by gas-pressure springs, and fixed in place again against the windscreen frame. The side windows are automatically lowered during the closing process to reduce the effort required to move the soft-top into place. The folded roof does not encroach into the load space. You will need to pay extra for the ‘wind protection insert’ — a rather minimal take on the mesh structure used on many open cars to reduce wind turbulence in the passenger compartment.

Air-bags for the head and thorax of the occupants are built into the seats. A tyre defect indicator is fitted, though a spare wheel isn’t.

The Roadster is fitted with an active rear spoiler, integrated into the tailgate. It extends automatically when the car reaches 50mph and retracts at 37mph. Predictably, the spoiler can also be operated manually for ‘washing’ (posing). The spoiler provides up to 40kg of downforce when travelling at maximum speed. As usual with Minis, the drag coefficients recorded by the various Roadster models are rather poor.

BMW Mini Cooper Cooper S Cooper SD John Cooper
Works
Cylinders 4I 4I 4I 4I
Block/head Al/Al Al/Al Al/Al Al/Al
Valves 4 4 4 4
VVT IE IE IE
Aspiration/
geometry
A Tts T/v Tts
Bore/stroke 77.0/85.8 77.0/85.8 84.0/90.0 77.0/85.8
Swept volume 1598cc 1598cc 1995cc 1598cc
Compression
ratio
11.0:1 10.5:1 16.5:1 10.0:1
PS/rpm 122/6000 184/5500 143/4000 211/6000
Nm/rpm 160/4250 240/1600 (1) 305/1750 260/1850 (2)
Maximum speed 123 141 131 147
0-100km/h 9.2 7.0 8.1 6.5
Urban MPG
(l/100km)
39.2
(7.2)
37.6
(7.5)
53.3
(5.3)
29.4
(9.6)
Combined MPG
(l/100km)
49.5
(5.7)
47.0
(6.0)
62.7
(4.5)
38.7
(7.3)
CO2 g/km 133 139 118 169
Emissions EU5 EU5 EU5 EU5
Transmission
— I
— II
— III
— IV
— V
— VI
— Final drive
M6 (A6)
3.214
1.792
1.194
0.914
0.784
0.683
4.353
M6 (A6)
3.308
2.130
1.483
1.139
0.949
0.816
3.706
M6 (A6)
3.308
2.130
1.483
1.139
0.949
0.816
3.706
M6
3.308
2.130
1.483
1.139
0.949
0.816
3.706
Driven wheels Front Front Front Front
Fuel tank 40l 50l 40l 50l
Kerb mass † 1120 1185 1200 1185
PS/t 109 155 119 178
Nm/t 142 202 254 219
Length 3728 3734 3734 3758
Width 1683 1683 1683 1683
Height 1384 1390 1390 1391
Wheelbase 2467 2467 2467 2467
Track
— front
— rear

1459
1467

1453
1461

1453
1461

1453
1461
Brakes
— front
— rear

Dv280
D259

Dv294
D259

Dv294
D259

Dv316
D280
Tyres 175/65R15/84H 195/55R16/87V 195/55R16/87V 205/45R17/84W
Steering ratio 14.1 14.1 14.1 14.1
CdxA (m²) 0.35x1.97 0.37x1.97 0.37x1.98 0.36x1.99
† DIN kerb mass. For E.U. kerb mass, add 75kg.
(1) Overboost: 260Nm at 1730rpm; (2) 280Nm at 2000rpm.
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