BRIEF­ING

Why the new fuel econ­omy and emis­sions test could lead to lighter, nat­u­rally as­pi­rated per­for­mance cars

Evo - - CONTENTS - by JOHN BARKER

John Barker in­ves­ti­gates the per­for­mance car’s weight prob­lem and a po­ten­tial so­lu­tion, Porsche re­veals its new GT3 RS and Dany Ba­har is back!

WSo why can a car that ar­rives for test weigh-in at 50kg or more in ex­cess of what its maker claims? It doesn’t add up

E LIKE WEIGH­ING CARS here at evo. We have a set of cal­i­brated scales that al­lows us to mea­sure the cor­ner weights to an ac­cu­racy of a few kilo­grams, so, as with per­for­mance and econ­omy fig­ures, we can find any sig­nif­i­cant vari­ance from what a car maker claims. We care about weight be­cause it in­flu­ences how a car drives, af­fects all dy­nam­ics – ac­cel­er­a­tion, brak­ing and cor­ner­ing. It also af­fects fuel econ­omy and emis­sions, and that’s about to be­come much more im­por­tant for new cars.

So why can a car that ar­rives for test weigh-in at 50kg or more in ex­cess of what its maker claims? The evo Su­pertest in is­sue 240 fea­tured the MercedesAMG C63 S Coupe, which has a quoted kerb weight of 1725kg. That made it the heav­i­est car present by some mar­gin, but on our scales the test car came in at 1847kg. Op­tion­ally, it had a panoramic glass sun­roof (circa +15kg) and Burmester stereo up­grade (circa +10kg), but also had the op­tional car­bon-ce­ramic brakes (circa -20kg). It doesn’t add up.

So why can vari­ances oc­cur? Some car mak­ers have a ‘trim level zero’ that lacks heavy fea­tures such as air con­di­tion­ing and elec­tric seats, but which can’t be re­quested. Or the kerb weight as­sumes the fit­ment of ex­pen­sive op­tions such as spe­cial al­loy wheels, car­bon brakes, bon­net, roof, etc, or the man­ual gear­box that has a mere five per cent take-up rate.

Change is com­ing, though, for car mak­ers and car buy­ers, with weight com­ing un­der in­creas­ing scru­tiny. The cur­rent fuel con­sump­tion and emis­sions test that car mak­ers self-cer­tify against – the NEDC (New Euro­pean Driv­ing Cy­cle) – is about to be re­placed. The NEDC was de­signed in the 1980s and does not re­flect fuel econ­omy fig­ures and emis­sions in real-world use. Its re­place­ment, WLTP (World­wide Har­monised Light Ve­hi­cle Test Pro­ce­dure), has been de­signed to be more rep­re­sen­ta­tive; it’s a 30-minute test (ten min­utes longer) based on re­al­world driv­ing pat­terns, and sub­se­quently in­cludes more speed phases and a higher av­er­age and top speed.

In the NEDC test, mod­els were clas­si­fied within weight bands, and a sin­gle model with the low­est kerb weight and low­est rolling re­sis­tance would take the test.

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