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Real world MPG versus official figures

The Prius is definitely on shaky ground. It is possible to achieve it's claims, but you have to drive it in a particular way...something that seems to be very tricky to do, and is quite slow!

The wife's Jazz consistently averages 40mpg, even though she spends most of her time in town
 
It is possible emulate manufacturers' claims, but only if you drive in a very economical manner. A long time ago, mercedes cars came with an insert slip in the manual which gave mpg at constant 90kmh and constant 120kmh. I got this slip with the W124 but not the W202 . The point is I could beat the 90kmh mpg - but only by going constantly a little slower on a long long motorway trip. I think the constant speed mpgs were much easier to understand and allowed you a better comparison against the real world.
Les
 
Anything other than constant speed consumption is at the mercy of weight. Carrying a passenger (say an extra 80kg) you're never going to match the published figures where acceleration/deceleration is involved. Aircon is a significant factor with small cars too, bet the manufacturers figures are with it switched off!

Also, I wonder how accurate a typical trip computer is when giving MPG figures?
 
BTB 500 said:
Also, I wonder how accurate a typical trip computer is when giving MPG figures?

I recently checked this with my £1500 Volvo 850.

1,800 miles round trip to France, it showed me an average of 26.7mpg. Using the odometer and my fuel receipts, I worked it out to 26.2.

I'm pretty happy with that kind of accuracy.

(the OTG also read in excess of 42deg for long periods od time, when parked in the shade and when moving. I'm inclined to beleive that too :eek:)

PJ
 
imadoofus said:
I'm pretty happy with that kind of accuracy.
What? It thinks you used about 5.85 litres less than you did, nearly 2% error! ;)
 
This is the problem. The tests have little connection with real world driving conditions

Urban cycle
The urban test cycle is carried out in a laboratory at an ambient temperature of 20°C to 30°C on a rolling road from a cold start, i.e. the engine has not run for several hours. The cycle consists of a series of accelerations, steady speeds, decelerations and idling. Maximum speed is 31 mph (50 km/h), average speed 12 mph (19 km/h) and the distance covered is 2.5 miles (4 km).

Extra-urban cycle
This cycle is conducted immediately following the urban cycle and consists of roughly half steady-speed driving and the remainder accelerations, decelerations, and some idling. Maximum speed is 75 mph (120 km/h), average speed is 39 mph (63 km/h) and the distance covered is 4.3 miles (7 km).

Combined Fuel Consumption Figure
The combined figure presented is for the urban and the extra-urban cycle together. It is therefore an average of the two parts of the test, weighted by the distances covered in each part.
 
Standards

It's all a question of standards. Whilst cars of a type are all fairly similar, no two drivers or thier typical journeys are. So has any body got a better standard for comparing likley real world fuel economy?
I happen to exceed MB's figures all the time in my E220, but most of my driving is done at legal speeds on main roads not in town traffic. I will be much better off that a city dweller in a hurry.
The published figures are, as they say, and indication of fuel economy not gospel. Why is it that so few people understand Newtons law's?
 

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