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