Real MPG and real emissions

Some friends are looking to change car soon. They are obsessed with emissions issues and look for low MPG cars with low carbon. Their current car (Smart) does not come remotely close to its real MPG. Its predecessor (Skoda Fabia 1.9 TDI) always did as claimed.

To obtain real emissions, would a reasonable proxy be to uplift the carbon value by claimed MPG over Real MPG? If so their Smart is only marginally better on emissions than their old Fabia which achieves 101% of its claimed MPG figure.

Asked on 10 October 2016 by Busmanuk

Answered by Honest John
Absolutely. If a car gets half the NEDC combined fuel economy it is by definition using twice as much fuel and emitting twice as much CO2.
Similar questions
I purchased a brand new Hyundai Tucson Ultimate and I am generally happy with all the toys. But two big disappointments to me are the fuel economy and very hard ride. I did take a test drive and thought...
I am looking to buy a small petrol car which has a big range. I have family who live in Currie, Edinburgh, approximately 400 miles away from where I live. I am looking for a small car that can do this...
I have a Vauxhall Insignia and all seems mechanically sound with 68000 miles on the clock, a recent service and full service history plus new discs brakes all round. When I bought it I was getting around...