Why are new cars not more fuel efficient than older ones?

Mudassir Ali
Feb 15, 2020 04:58 AM 0 Answers
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Mudassir Ali
- Feb 15, 2020 04:59 AM

There are a number of possible reasons.

The standards for measuring fuel consumption sometimes change, this can result in the test having to be performed differently or with a higher loaded mass, which degrades fuel economy. For ADR (Australian Design Rules) fuel consumption testing, a vehicle’s inertia class (mass) determines how much ballast it must cary for the test or parts there of.

Over the years (and model updates) cars typically get larger and heavier for the same model. Increased mass, frontal area and drag have a negative impact of fuel economy.

There are many reasons why cars tend to get larger and heavier. Saftey ratings and consumer metric tests like NCAP often drive vehicles towards a stiffer / stronger body structure (meaning more metal) and more airbags (though these are not that heavy). Increased feature content and electrification such as powered seats, sunroofs and electric tailgates all add mass as do larger diameter, often wider, wheels and tyres. The desire for better occupant packaging often means the vehicle gets stretched to allow more leg room compared with a previous model. Finally improved opulance and reduced NVH (Noise, Vibration and Harshness) requires more body deadener, sound insulators and even thicker glass (which is heavier than most people realise).

Technology has come a long way. Engines are more efficient, light weight materials and high strength steels (which can be thinner and lighter) get used, along with improved aerodynamics and low rolling resistance tyres, but these only help so much. When the other factors mentioned above become a more significant influence, then fuel economy suffers.

However fuel economy is not the only measure of a car’s performance. Generally speaking, new models are quieter, more comfortable and usually a lot safer.

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