To Mill­brook for ac­cel­er­a­tion and brak­ing tests – and a po­ten­tially em­bar­rass­ing weigh-in

Evo - - DRIVEN -

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.

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