Real World Fuel Economy

Real World Fuel Economy

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Peter De Nayer, veteran specialist in technical research and fuel economy and performance evaluation carries out real world fuel consumption tests and has generously offered the disparity results to Group members and visitors to the SGMW site.

If you would like Peter’s full results on the cars you are assessing, contact him by E Mail at:

Peter says:

“These ‘Real World’ fuel consumption figures are obtained by driving pre-set test cycles on traffic-free roads, with no random interruptions caused by other traffic. All car instrumentation is corrected before commencing the tests and the target ambient temperature is 10 degrees C, with dry surfaces and low wind speed; the test routes are circular. The car is normally equipped with a fuel flow meter on the delivery side of the engine, which provides an accurate measure of the fuel being consumed in millilitres – 4546 to the gallon.

The URBAN test is a programmed series of stops and starts over a 3.2 mile route, with brief periods of acceleration and cruising up to 40mph; the car is stationary for 27 per cent of the time and the average speed is 16mph.

The RURAL test also has a maximum cruising speed of 40mph but the driving style is much more leisurely and there are no periods of idling, although there are ten junctions over the 10 miles of A and B roads, with an average speed of 30mph.

These two tests establish the normal mpg range for everyday extremes of use; however, the MIXED USE result is not the mean of these two extremes. Three other test cycles are conducted as well – Motorway/70 cruising, Short Journey/Suburban (from a cold start), plus Out of Town/Brisk but Legal.  Between them, the five encapsulate every (legal) driving style and traffic condition one will experience in the UK.

All five results are ‘Combined’ (like the two NEDC cycles, to produce the mileage-weighted MIXED USE AVERAGE; the mileage mix for this calculation is 7% Urban, 13% Suburban, 30% Brisk, and 25% each for Motorway and Rural. This will provide an accurate indication of the car’s overall fuel economy for the user who ‘does a bit of everything’ and is useful for comparison with rivals. However, prospective owners can reliably calculate their own anticipated Overall MPG by adjusting the figures to suit their own pattern of use.”

Peter goes on to say:

“As you can see, the two results are very close in 10 per cent of the cars, yet nearly half of them are more than 20 per cent adrift – so much for the ‘Level Playing Field’ justification for the NEDC (New European Driving Cycle) testing regime.”

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