Manufacturer MPG claims

[obi_waynne]

How accurate are MPG claims by manufacturers? It seems that they can do these tests in perfect lab conditions and there is also some leeway in the speeds they have to maintain.

I'm assuming that an auto is more likely to be accurate than a manual. The most shocking figures seem to come on Turbo's with the tests being typically run off boost and on boost MPG figures are half of those claimed!

What has been your experience? How much do you add to the MPG figures to make it accurate?

 

[HDi fun]

The lab like conditions mean that even though the figures themselves will never actually be accurate but because of the stringent criteria you can at least compare between different makes and models.

 

[stamford]

What he said ^^ just use the figures as a comparator and make your own mind up as to what they might be. Other than that check out owners forums on mpg figures before looking to buy.

 

[WLBjork]

Pretty decent.

On a "normal" drive they're a little short, but not too bad.

On a "good" drive - that is, I don't have to stop for any junctions, and at optimum acceleration, I can - on a 5 mile journey, most of which is limited to 30mph - get close to the extra-urban mpg.

Then I have to take 10% off for the inaccuracy of the computerised mpg widget

 

[bigbadjoe]

This was on watchdog a few weeks back.

I have always had quite good luck when it comes to MPG. Ok, that is according to the cars that I have had. The worst was the mazda. Averaging about 25mpg. My Evo, yes averages 18mpg driving around but I expected that. What I didn't expect to get was 31mpg on the motorway with her!! That was a nice suprise!!

I wouln't go by what the manufacturer's say tho, Id find out using forums and what not.

At the end of the day, I find, the bigger engine cars are more acurate with there manufacture mpg claim, as they have nothing to lose, where as the little ''fuel savers'' the manufactures squeez every last drop out of the car so they can back up there claims.

 

[HDi fun]

It's much simpler than this. None of us does an average journey. So the testing authorities have quite simply created laboratory sample journeys. At least this way the test is repeatable and reliable.

Much like CO2 figures. Depends on driving style. Perhaps it should be banded much like CO2 figures.

 

[bigbadjoe]

CO2 figures are a joke anyway.

Why pay more for the more CO2? There is no machine out there turning all this CO2 back into O2 is there.

Mind, I dont ever have the mpg problem. Always buy second hand, so after research will find the mpg range.

HDI, the manufacturer will find the best mpg at a certain speed in a certain gear (say 5th gear at 54mph) and run the car from a full tank to an empty one on a rolling road.

No wind involved, No alteration in speed. No traffic lights. Nothing. Constant speed. This is why manufacture figures are unfair to the users.

 

[HDi fun]

That is no longer the case. In the 1980s this was common practice and the makers would jet the carbs to be super lean at whatever revs coincided with exactly 56mph in fifth gear and then do as you said. This is how the myth came about that 56mph was the most economical speed.

The current urban/extra-urban/combined cycles are much more rigorous and repeatable.

CO2 figures are a joke anyway.

Why pay more for the more CO2? There is no machine out there turning all this CO2 back into O2 is there.

Mind, I dont ever have the mpg problem. Always buy second hand, so after research will find the mpg range.

HDI, the manufacturer will find the best mpg at a certain speed in a certain gear (say 5th gear at 54mph) and run the car from a full tank to an empty one on a rolling road.

No wind involved, No alteration in speed. No traffic lights. Nothing. Constant speed. This is why manufacture figures are unfair to the users.

 

[obi_waynne]

The new triple band MPG figures quoted are useful for comparison. It makes more sense than the old single figure. But manufacturer figures are still way out and not by the same percentage.

Some cars fail to achieve the quoted MPG figures by over 30%. Surely if you granny the car you should be able to get near to the manufacturer figures.

What is your MPG figures like compared to what they should be? Does this bother you much?

 

[Yugguy]

I posted a link a while back showing that nearly all were wildly innaccurate, apart from Aston Martin's.

 

[st24]

The new triple band MPG figures quoted are useful for comparison. It makes more sense than the old single figure. But manufacturer figures are still way out and not by the same percentage.

Some cars fail to achieve the quoted MPG figures by over 30%. Surely if you granny the car you should be able to get near to the manufacturer figures.

What is your MPG figures like compared to what they should be? Does this bother you much?

My car is supposed to do 59mpg overall according to the tests.
I knew this would never happen the best I have seen is 44mpg.
However I don,t always drive with economy in mind.
And no it does not bother me in the least.

 

[VladimirKoteski]

Manufacturers remove anything that would cause extra drag such as side mirrors etc.. and they test cars on sea level to get better numbers.Technically their numbers are accurate for the conditions they test it on however not in real life.Like people claiming audi a4 tdi quattro with 180 hp does 5l/100km which is impossible as it does 8 to 10l if ypu drove like a granny that is.

 

[HDi fun]

Not sure it's quite that contrived any more.

 

[Guybo]

I always thought they set the cars (in the US anyway) to 55 mph on a car treadmill and measured the MPG that way. This fantasy number doesn't take into account aero drag. That's why mileage drops off a cliff at about 60 MPH- aero drag really starts to kick in at 60 and it's over the 55 mph target sweet-spot manufacturers aim for.

 

[HDi fun]

In the pre cat days manufacturers could design in a very lean mixture at the rpm which corresponded to 56mph in top gear.
The official testing process in Europe is not representative of real world driving BUT it is at least consistent across all makes and models thus offering the consumer a means of comparison.

http://www.theaa.com/motoring_advice/fuels-and-environment/official-fuel-consumption-figures.html