I`m referring to real life *cold multi stop start* usage where the engine temp gauge never gets off the peg in winter.
Does the `urban` figure actually reflect this usage? when a Diesel in real life is vastly superior under these circumstances.
Just how many stop starts from cold ( and I mean a temperature and usage that would have a petrol running constant enrichment) over what mileage is done to get the figures.
Because I`m suggesting that the `urban` figure is not the definitive test for multi cold stop start work and it has generated a myth that only high mileage saves money with a diesel.
Regards
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From the VCA website;
Urban Cycle:
The urban test cycle is carried out in a laboratory at an ambient temperature of 20oC to 30oC 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 31mph (50km/h), average speed 12mph (19km/h) and the distance covered is 2.5 miles (4km).
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 75mph (120km/h), average speed is 39mph (63 km/h) and the distance covered is
4.3miles (7km). Combined Fuel Consumption Figure:
The combined figure presented is for the urban and extra-urban cycle together. It is therefore an average of the two parts of the test, weighted by the distances covered in each part.
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Thank you for that Gongfarmer, I tried to find it and couldn`t
It confirms what i thought about temperatures. Only one `cold` ( if you can call 30C that) start . Perhaps they should reset the temperatures to 4c to be representative of winter.
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My Rovers combined figure when new was 49.2, I get 48-52 in mixed driving, about 46 urban, which is less than 1 mpg off the 47 odd gov figures say for this car, so I would say they are fairly accurate atleast as far as my car is concerned. And my car is 12 years old and not at its best.
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Sure, i`m not saying their figures are wrong. Just that a real life (extreme) stop start usage doesnt reflect the test. The fact that they can test at 30C says it all really.
Example, Its on freezing point, you`re a home care worker, stop starting every few hundred yards all day. 3/4 hours between stops with an icy wind blowing onto the engine.
There`s no way that usage is reflected by a start and run at 20 to 30c for 2.5 miles on a rolling road.
It favours the petrol engine
Edited by oilrag on 23/01/2008 at 21:07
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The MPG figures aren't supposed to conform to anyone's real usage. All they provide is a benchmark, a consistently applied series of tests which allow you to compare car A with car B when buying.
There are all sorts of usage patterns which will give you a variation from the results of the official tests - probably the most common in the UK being sitting in a traffic jam "engineered" by the donuts in the town hall!
Number_Cruncher
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I'm baffled by the 20-30 degree cold starts. When UK started with standard tests, 75, 56, Urban we simply adopted California emission tests. This was heavily criticised because of the warm "cold" start - I thought that subsequent EC tests used a much lower temperature to be more representative.
To emphasize NC's point, the whole objective of consumption figures is to allow comparison between models, free of individual manufacturers marketing spin.
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sure I agree, but it doesn`t show a real world comparison between petrol and diesel in UK winter, multi cold stop start motoring.
Amazing that we just used a California test schedule, a warm country figure that minimises the fuel consumption deficiencies of a petrol engine running, one 30c ! start enrichment.
That doesn`t reflect our home care workers winter use, or for that matter, recently retired`Auntie Nellie` who only goes to the shops, church and visiting her friends in the village.
Problem is, `Auntie Nellie` has been told that diesel will only benefit her if she drives 20,000 miles a year pulling a loaded twin axle trailer with a `Worrier` road tractor.
In reality she could save a high percentage of her fuel costs by buying that £6,300 diesel Panda, rather than the petrol version that would, in her usage, spend the next 15 years of her motoring retirement, guzzling along on permanent fuel enrichment.
Regards
Edited by oilrag on 24/01/2008 at 07:54
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Why do you think that diesel cold start is more efficient than petrol. According to the on board (inaccurate) mpg consumption indicator on my 1.6 HDi Picasso, enrichment lasts for about 5 miles in the morning. It heavily increases consumption for this time. It takes about 6-7 miles before the heater output becomes effective. A benefit of modern lightweight diesel technology?
My old BX 1.7 turbo was overall about as economical and warmed up much quicker.
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>Example, Its on freezing point, you`re a home care worker, stop starting every few hundred yards all day. 3/4 hours between stops with an icy wind blowing onto the engine<
I hope my home care worker - if I ever need one - will be driving a petrol runabout.
At least I can be sure she'll have clean hands...
;-)
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She`ll wear latex gloves when washing you down Mike ;) , wouldn`t want to take anything home..
So I`m told ;);)
Regards
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I won't take it personally but wow, I can hardly wait...
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SWMBO has taken note and is sending her male co-worker who used to be a fireman. ;);)
Regards
( nothing personal of course, just a little humour ;)
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Not much support for a more representative, UK temperature, test then? ;)
Regards,
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Not much support for a more representative UK temperature test then? ;)
The tests use EC standards. A UK test might give different numbers but make virtually no difference to the comparison between different models, which is the objective of the tests.
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>>probably the most common in the UK being sitting in a traffic jam "engineered" by the donuts in the town hall!>>
I agree!
Much more could be achieved in lowering motoring derived CO2 by investing in the roads system to free up traffic flow and raising average speeds AND raising average MPG AND thus shortening journeys, a WIN WIN WIN situation, than by legislating people into ever more economical cars.
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