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The great fuel consumption poll

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View Poll Results: Please select the option closest to what applies to you...
3.2 AWD & FWD - 18 to 25 MPG (US 15-21) 15L/100km - 11L/100Km 1 0.25%
3.2 AWD & FWD - 25 to 33 MPG (US 21-27) 11L/100km - 8.5L/100Km 1 0.25%
3.2 AWD & FWD - 33 to 45 MPG (US 27-37) 8.5L/100km - 6.3L/100Km 0 0%
T6 AWD - 18 to 25 MPG (US 15-21) 15L/100km - 11L/100Km 10 2.54%
T6 AWD - 25 to 33 MPG (US 21-27) 11L/100km - 8.5L/100Km 13 3.30%
T6 AWD - 33 to 45 MPG (US 27-37) 8.5L/100km - 6.3L/100Km 3 0.76%
D5 AWD - 18 to 25 MPG (US 15-21) 15L/100km - 11L/100Km 3 0.76%
D5 AWD - 25 to 33 MPG (US 21-27) 11L/100km - 8.5L/100Km 91 23.10%
D5 AWD - 33 to 45 MPG (US 27-37) 8.5L/100km - 6.3L/100Km 162 41.12%
2.4D DRIVe - 18 to 25 MPG (US 15-21) 15L/100km - 11L/100Km 3 0.76%
2.4D DRIVe - 25 to 33 MPG (US 21-27) 11L/100km - 8.5L/100Km 7 1.78%
2.4D DRIVe - 33 to 45 MPG (US 27-37) 8.5L/100km - 6.3L/100Km 38 9.64%
D3 DRIVe - 18 to 25 MPG (US 15-21) 15L/100km - 11L/100Km 1 0.25%
D3 DRIVe - 25 to 33 MPG (US 21-27) 11L/100km - 8.5L/100Km 4 1.02%
D3 DRIVe - 33 to 45 MPG (US 27-37) 8.5L/100km - 6.3L/100Km 57 14.47%
Voters: 394. You may not vote on this poll

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Old Mar 23rd, 2012, 12:56   #21
wimorrison
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Originally Posted by jimbg View Post
I had a long debate on another thread about mpg, the fuel consumed figure will be very accurate but the distance measurement is the area of possible concern.

But, does the speedo over-reading actually correlate to any error in the distance traveled? Or is the speedo over-reading independent of the distance run?

Need to take a GPS on a very straight road on cruise control to compare speed.

Not sure how to check distance accuracy?
The speedo is only a reflection of the number of times that the wheel has rotated and thus the distance travelled for each rotation of the wheel. The car is 'programmed' to expect a set distance for each revolution of the wheel and as the tyre wears you travel less distance though the car thinks you have gone the same distance and because of this the fuel consumption will appear to get worse as the car thinks you have used more fuel to cover the theoretical distance. The wear effect will be amplified with under-inflation, reduced with over-inflation ~ perhaps this over-inflation effect is the reason the high pressure (39PSI) is called the 'eco mode'

As you suggest a GPS is needed to remove the tyre variation in the distance traveled and speed - many GPS will give you both instantaneous speed and distance travelled from a set point.

@volvorocks - clearly I missed your posts on the subject and I seek forgiveness.
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Last edited by wimorrison; Mar 23rd, 2012 at 13:00.
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Old Mar 23rd, 2012, 13:17   #22
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@volvorocks - clearly I missed your posts on the subject and I seek forgiveness.
You are forgiven

Seriously though, to everyone, I am surprised no one actually considered the theory, so its good it has been brought up again.I think a simple theoretical example I gave was, if there was 100 miles on the trip and 1 gallon had been used then people would work that out as 100mpg using the brim to brim calculations, when in fact, as you also say, due to speedo error, the actual distance travelled may have been say only 95 miles which would equate to 95mpg.

When working out my MPG using miles travelled and fuel used, then whatever figure I arrive at I reduce it by 4% , to be on the safe side.

Regards

EDIT:
I find 32mph on the speedo=30mph and 77mph=73mph.Based on GPS and those flashing "your speed is" town signs Anyone else have any figures like this?

Last edited by volvorocks; Mar 23rd, 2012 at 13:24.
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Old Mar 23rd, 2012, 13:43   #23
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Originally Posted by wimorrison View Post
The speedo is only a reflection of the number of times that the wheel has rotated and thus the distance traveled for each rotation of the wheel. The car is 'programmed' to expect a set distance for each revolution of the wheel and as the tyre wears you travel less distance though the car thinks you have gone the same distance and because of this the fuel consumption will appear to get worse as the car thinks you have used more fuel to cover the theoretical distance. The wear effect will be amplified with under-inflation, reduced with over-inflation ~ perhaps this over-inflation effect is the reason the high pressure (39PSI) is called the 'eco mode'

As you suggest a GPS is needed to remove the tyre variation in the distance traveled and speed - many GPS will give you both instantaneous speed and distance traveled from a set point.

@volvorocks - clearly I missed your posts on the subject and I seek forgiveness.

As you say the car is programmed to calculate speed from the tyre revolutions. But my question is, does this calculation then deliberately introduce the speedo over-read? I only ask because the distance traveled does seem to be fairly accurate?
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Old Mar 23rd, 2012, 14:05   #24
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Speedo's over read by around 10% as a safety margin for mfrs. Imagine if they under read and you were given a speeding ticket for going over the limit when your speedo read under. US lawyers would have a field day and bankrupt mfrs in no time.

Some are more extreme than others, I believe Peugeots are at the high end but 7-10% over read is pretty standard. Your satnav will be pretty close to spot on so check what that reads when your speedo is doing 30, 40, and 70mph to see how your own car fairs.
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Old Mar 23rd, 2012, 14:14   #25
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EDIT:
I find 32mph on the speedo=30mph and 77mph=73mph.Based on GPS and those flashing "your speed is" town signs Anyone else have any figures like this?
At 30mph mine is 2mph out then it seems to be consistently 3mph out throughout the rest of the speed range, although I haven't tested beyond 70mph.
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Old Mar 23rd, 2012, 14:58   #26
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Speedo's over read by around 10% as a safety margin for mfrs. Imagine if they under read and you were given a speeding ticket for going over the limit when your speedo read under. US lawyers would have a field day and bankrupt mfrs in no time.

Some are more extreme than others, I believe Peugeots are at the high end but 7-10% over read is pretty standard. Your satnav will be pretty close to spot on so check what that reads when your speedo is doing 30, 40, and 70mph to see how your own car fairs.
The speedo may over-read by 10%, but the distance does not!

Otherwise over a 100 mile trip, it would show 110 miles and it most definitely does not.
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Old Mar 23rd, 2012, 18:40   #27
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......

Not sure how to check distance accuracy?
Measured over a reasonable straightish stretch on a decent map?
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Old Mar 29th, 2012, 00:19   #28
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Default Tanker Drivers "possible" protest & panic buying!

There is a lot of people over the last 2 days who have started to drive a lot slower as if in "Fuel Saving Mode"........!!!
Maybe it's the additional weight of carrying arround a full tank or perhaps a boot full of topped up jerry cars as advised today by the Transport Minister.

It's amazing how we (excluding self) panic when we hear about a fuel shortages and instead of a weekly £20 fill up suddendly start filling the tank to the brim with £100's worth of fuel. Even a non-accountant can work out that in one day we have suddendly increased demand by a factor of x 5.
What's the betting that tomorrow we start hearing about fuel £ cappings or garages running dry.............oh dear..........how predicable.
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Old Mar 29th, 2012, 00:51   #29
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There is a lot of people over the last 2 days who have started to drive a lot slower as if in "Fuel Saving Mode"........!!!


It's amazing how we (excluding self) panic when we hear about a fuel shortages and instead of a weekly £20 fill up suddendly start filling the tank to the brim with £100's worth of fuel.
Maybe people have started driving slower,yes I agree.

£20 a week though is slightly low do you not think?

The bit in red.....Really??

Most people want fuel or rather need fuel!!

What about businesses that need fuel for deliveries?...Surely they will fill up in anticipation?....or is the post to discourage the public from filling up in order to leave more for business needing fuel for delivery?

I am currently re designing my garden and have ordered some fencing and trellis along with a pergola from a very reputable reliable honest company up in Scotland and I do look forward to a reliable delivery

Regards

Last edited by volvorocks; Mar 29th, 2012 at 00:55. Reason: Crikey I spelt Discourage incorrectly!
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Old Mar 29th, 2012, 14:57   #30
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I am currently re designing my garden and have ordered some fencing and trellis along with a pergola from a very reputable reliable honest company up in Scotland and I do look forward to a reliable delivery
VR. Who are you buying it from out of interest?
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