The only truth in the above quote is the fact the tests are done on a rolling road.

On a rolling road there is no wind resistance since the car is stationary, this is factored in later using manufacturers figure which may or may not be accurate.

But taking off the mirrors and taping up gaps would achieve nothing. And disconecting the brakes would make slowing down during the various phases of the test very difficult.

Reality check required (or listen less to pub talk).

Havent read too much of the above replies here but heres my input...

Yes, the tests are done on a rolling road, etc etc. BUT the rolling road is set up with drag factors to simulate rolling and wind resistance. These drag factors, often supplied by the manufacturer, are obtained by running a "production" vehicle in neutral on a level test track at some speed then measuring the distance it rolls to a stop. Several runs back and forth etc ensure "accurate" factors are generated.

This is where the selected vehicle, tyres (e.g. obscure eu base model with eco variant skinny tyres), taped up gaps etc etc sneek into the equation.

Thats my understanding.

Edited by brum on 23/06/2015 at 00:49

To get good MGP it's temping to run an engine lean, remember all the old lean burn engine of the 1990's. (Those produced loads of NOX). Ford has taylored the output to have NOX within EURO 6 limits and no more. when the car is rigged to pass a test.

Compare a VW up engine of 74hp with a 1.0t 100 or 125hp is unrealistic at best. Sadly VW don't have a direct alternative at it falls between the 1.2/1.4tsi engines. For example Ford has a CO2 output of <99g/km with the VW UP 74 hp engine alread at 108g/km. The Bluemotion 1.0 up seams quite able to average around 55mpg. rather better than the fords at 45mpg. This is simply comparing "apples and pairs" as we dont have the same power output. So we have to look at equ. powered engines else ware in the VW 1.2tsi/1.4tsi engines range and back to around the 45mpg once more.

That leaves the open question is nox worse than co2? well NOX is a group of gases not one gas. The new 5 gas analysers don't appear to provide breakdown for what NOX gas is detected in NO2?.So basically it's seams a question with no clear answer (NOX = Smog?).

So until testing standards relate to real world experences I see testing as close to pointless and only usable for TAX calculation purposes.