If the additional 45kg added to the Mazda’s weight by a metal roof raised eyebrows, the Merc’s 350kg handicap over its Japanese rival calls for Botox injections. However, the SLK is 23bhp and 51lb ft to the good versus the naturally aspirated, 158bhp MX-5 RF, and is both quicker to 62mph (7.0sec against 7.4sec) and more frugal (43.5mpg beats 40.9mpg).
Inside, the SLK is unsurprisingly ritzier. Soft-touch and satin-effect surfaces abound, complementing the leather upholstery and solid, precise switchgear. Ergonomics are equally hard to fault, with firm, enveloping seats that can be set low enough to leave sufficient cranial clearance for a tall driver when the roof is up. A boot divider must be in place before the SLK’s lid can be lowered. It slashes the load capacity from 335 litres to 225, but either configuration easily trumps the MX-5’s meagre 127.
Efforts to suppress cost and weight define the Mazda’s cabin. The stripped-back feel suits the car’s intentions, but you can’t ignore the shortfalls in tactility, adjustability and robustness compared to the SLK. Its seats match the Merc’s for support, but minimal vertical adjustment leaves me a little high, with bonce brushing roof. The steering wheel won’t adjust for reach, there’s no glovebox and the centre console’s infotainment dials are sited too far back to be easy to reach.
However, this being Sport Nav trim, the Mazda gets welcome toys that are missing from the Mercedes, including a responsive 7.0in touchscreen with sat-nav (the SLK’s 5.8in screen is inert and nav-less), rain, dusk and rear parking sensors and heating for its leather seats to broil your behouchie during chilly al fresco sorties.
Firstly, we race the cars without turning a wheel. The Mazda’s elaborate up-and-under folding routine takes the spoils in our top-dropping competition, its roof collapsing in 15sec compared with the more straightforward Mercedes’ 20sec. Neither one requires manual intervention.
Igniting the MX-5’s engine brings a subtle vibration to the cabin. The unit sounds bland when you pull away, but there’s steadfast urge from 1500rpm, and once you’re exploring the purple patch between 3000rpm and the red line’s 6500rpm there is vibrant throttle response, a decent amount of shove and a loud but racy soundtrack goading you on. More enjoyable still is the short-throw six-speed manual gearbox, whose gratifying mechanical action survives the most aggressive of shifts without flinching.
The SLK’s sports exhaust, which came as standard with our test car’s AMG Sport trim, emits some droning during low-speed operations, then a gruff chunter with turbocharged overtones ensues. It becomes quite noisy with revs, but delivers neither the brashness nor the character of the Mazda. Anything from 2000rpm lends the Mercedes strong progress and there’s little in the way of turbo lag, although acceleration wanes a bit at 6000rpm.
The cars are quite evenly matched for pep, but the Merc’s seven-speed torque converter (the prevailing SLK 200 transmission of choice) hampers it, with kickdown that’s not sharp enough and a wearing, one-second delay before it answers paddle inputs. The shifts themselves are quick enough, though, and whumphing exhaust theatrics add some muchneeded aural spice during upshifts in the Sport and Manual driving modes.
Both cars have tweaked chassis: stiffened, 10mm-lowered AMG Sport springs and dampers and thicker anti-roll bars on the SLK; a front strut brace and Bilstein dampers on the MX-5 RF Sport Nav. The Mercedes does without the adaptive dampers and unconvincing speed-sensitive steering of the Dynamic Handling Package that is offered as an option and is better for it, apart from a lowspeed ride that jars over ridges.
Where the Mazda rolls generously and endlessly bobs about on its much shorter wheelbase, the SLK – despite its ballast – is steadier and more settled. Although the steering is heavy and one-dimensional, it is accurate. Add good front-end bite and ample traction from its 245mm-section rear tyres and the SLK slips through corners with both comfort and speed. Tackle the same bends in the flyweight MX-5 RF and it’s like wiping away a layer of gloss: grittier, more dramatic and more involving, with snappier turn-in and more variation and discourse from the lighter steering. Roll is pronounced, but once the Mazda has hunkered down on its outside wheels, there’s a lovely, precise obedience from the steering as it awaits further instruction, with the car’s limitedslip diff primed for a swift exit.
Yet this victory – important though it is – cannot carry the day. With its roof in either position, the SLK is in a different league for refinement, with wind noise and turbulence tamed to levels the clamourous MX-5 can’t imagine. Cruising with the roof up, the aerodynamic roar behind your head and around the Mazda’s buttresses is plain loud, and supplemented by a booming engine. Top down, it can become oppressive. Combined with regular vertical hiccups, it left me surrendering to the SLK’s polish – even at the cost of outright engagement.
For affordable thrills, few cars can match the MX-5. If its formula appeals, save £2000 and go for the incredible value of the rag-top, because the RF can’t quite pull off the twin purpose it strives for. The second-hand SLK, tamer though it is, comes closer to hitting that mark.
1st place - Mercedes-Benz SLK 200 AMG Sport
Price new £36,710 Price now £21,000 Engine 4 cyls, 1796cc, turbo, petrol Power 181bhp at 5250rpm Torque 199lb ft at 1800-4600rpm Gearbox 7-spd automatic Kerb weight 1470kg 0-62mph 7.0sec Top speed 147mph Fuel economy 43.5mpg (combined) CO2/tax band 151g/km, 27%
2nd place - Mazda MX-5 RF 160 Sport Nav
Price new £25,695 Price now £25,695 Engine 4 cyls, 1998cc, petrol Power 158bhp at 6000rpm Torque 148lb ft at 4600rpm Gearbox 6-spd manual Kerb weight 1120kg 0-62mph 7.4sec Top speed 134mph Fuel economy 40.9mpg (combined) CO2/tax band 161g/km, 29%