To Millbrook for acceleration and braking tests – and a potentially embarrassing weigh-in
PARKED AT THE START OF the Millbrook mile straight, the C63’s engine is settled to a low, purposeful idle that hints heavily at the performance potential. Pull both aluminium gearshift paddles towards you to engage the launch mode, then tap the right one briefly to confirm you’re ready. Plant your left foot on the brake and your right foot on the throttle and wait for the V8 to start bellowing and crackling at a preset 3500rpm before side-stepping the brake and letting the computers do the rest.
It sounds easy, but in reality getting the rear-wheel-drive Mercedes off the line takes practice. Selecting the traction control’s halfway-house Sport setting and carefully feathering the throttle helps the C63 roar to 60mph in 4.3sec, which is a few tenths behind Merc’s claim of 3.9sec to 62 but an impressive achievement when you consider the C63 tips our scales at a portly 1847kg.
The carbonfibre-roofed M4 is far trimmer, weighing in at just 1645kg. This helps explain why it’s just a tenth slower to 60mph than the C63, despite a 59bhp power deficit. That’s about as big as the gap gets between these two, and remarkably they both flash past 150mph in 21.1sec. Launch control is standard, but as in the Mercedes it’s tricky to get the BMW off the line. You can alter the starting revs up to a maximum of 4000rpm, but even then the M4 feels like it’s bogging down on Millbrook’s track surface, possibly explaining why that 0-60mph time is four tenths behind BMW’S 0-62 claim.
No such worries for the Audi. Yes, it weighs a not insubstantial 1799kg, but fourwheel-drive traction and a gearbox that features eight closely stacked ratios allow it to erupt off the line without wasting a single horsepower. As in the M4 and C63 S, there’s launch control, yet unlike in those two, the Audi’s system is brutally effective. Out of the corner of my eye I can see Adam’s head being flung back against his headrest as the RS5 catapults off the line like a fighter jet being fired down the deck of an aircraft carrier. The result is 60mph in a laugh-out-loud 3.6sec. Audi modestly claims 3.9sec to 62.
However, the Audi’s mass and weaker top end tell eventually and beyond 100mph it starts to lose ground to the other two. By 150mph it’s a full two seconds in arrears.
Our braking test features ten consecutive stops from 100mph, which is enough to put even high-performance setups under strain. The Merc’s optional carbon-ceramics give the impression of refusing to wilt, the pedal action remaining resolutely firm. However, the data shows a 21.5-metre difference between the best and the worst stop – the largest spread here. The C63 also records the longest stopping distance, by over 5 metres.
The lighter BMW, on standard castiron brakes, stops in the shortest length, recording 86.5 metres early on – 1.6 metres better than the Merc’s best. However, during the eighth stop the pedal begins to go long and wisps of smoke rise from the underpressure pads. The Audi’s brakes – also castiron – suffer the same symptoms at about the same time, but unlike the BMW, the RS5’S pedal feel and brake bite are fully recovered by the time we hit the road again.