Member Since: 30 Jan 2010
Location: Sussex
Posts: 106
My first tank was a claimed 29.5mpg, but 25mpg in reality. Second fill up will be today, but it's claiming slightly less at the moment.
It seems like mpg calculators in cars/bikes are very inaccurate. Our BMW tourer bike claims 5-8mpg higher than reality, and that seems to be par for the course.
I'm going to reserve judgement on the mpg in the Disco until I've done a couple of thousand miles. One thing to bear in mind is that mpg figures are calculated using a rolling road, not real driving, so I think you're doing well if you get close to them! And technique makes a big difference...
I am going to calibrate my speedo with a roadangel, if the computer shows 27.7 average and i'm really getting 24.7, then there is a 10% over-read, so if my speedo shows 70 then i'm really doing about 64.
A new tyre (Scorpion Zero) is 75cm in diameter but can wear down by about 8mm. This is about a 2.0% variation in diameter, and hence in distance travelled per revolution. The computer on-board is counting revolutions, so this will affect the distance travelled figure used in the mpg calculation, and also the displayed road speed.
One could independently measure distance travelled using an external SatNav and a long straight road. Then one could calculate the correction factor for that vehicle at that time. We can't then apply that factor to any other vehicle, or use it once the tyres wear a bit, of course.
So comparing the displayed mpg between vehicles is somewhat meaningless. We cant even rely on using fill-to-fill calculations between vehicles because of this variation in distance measurement.
All that can be read into the numbers is whether they are better or worse than previous on the same vehicle.A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
Last edited by Navigator on 25th Apr 2010 11:54 am. Edited 2 times in total
A new tyre (Scorpion Zero) is 75mm in diameter but can wear down by about 8mm. This is about a 20% variation in diameter, and hence in distance travelled per revolution.
You might want to check your workings on this one...........
Edit: Answer is about 1% for new v's bald tyre. You're a navigator........ you'll work it out! The older I get, the more I realise that people confuse wrinkles for wisdom
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21st Apr 2010 4:50 pm
wobbly
Member Since: 25 Feb 2010
Location: Zumerzet
Posts: 50
I had a little play today, but am going to have another go tomorrow.
Firstly, roadangel doesnt like the disco windscreen, so attached it to the sunroof!
With the roadangel showing 30mph, the speedo shows 32mph
With roadangel at 40mph, the speedo shows 43mph.
Roadangel at 50mph, speedo shows 54mph.
didnt get to 60,but am guessing it will show 65, and 70 will record 76.
Thats showing some like 5 to 7% over-read, which is perfectly normal for a car and within legal limit.
I tend to drive off the roadangel speedo all the time, keeps me spot on legal, and I do tend to be slightly faster in things like 50mph average checks, which I put down to other vehicles using their speedos which are likewise over-reading.
Of course, from a mpg point of view this is worse, cos it means you havent actually driven the mileage shown, but about 5 - 7% less! Maybe best not to think about it.
No vehicle, with the exception of my Chevy G20 dayvan, has given me this much driving pleasure, so mpg not an issue, but am interested in seeing whether the mpg increases with use.
Cheers
PeteMay the road rise with you.
May the wind always blow at your back.
And the sun always shine on your face.
May God always hold you in the palm of his hand.
21st Apr 2010 8:50 pm
Winger Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
The speedo is set to over read; the odometer records the actual mileage. The fuel consumption is based upon actual mileage and fuel used, so the speedo overage does not impact on either a manual calculation or the optimistic onboard chappie.
The speedo over reads because it is electronically adjusted to do so. The formula used to adjust the indicated speed in the UK is speed+3.5%+2km/h.
21st Apr 2010 9:16 pm
wobbly
Member Since: 25 Feb 2010
Location: Zumerzet
Posts: 50
That makes sense, can see the obvious road safety angle.
did wonder about the odometer, but if they are set seperately then there is no adverse affect on mpg.May the road rise with you.
May the wind always blow at your back.
And the sun always shine on your face.
May God always hold you in the palm of his hand.
Relying on a GPS device for speed is not always accurate either - going up and down hills will affect the reading - the steeper the hill, the more the difference.
If you imagine a triangle, the vehicle travels along the hypotenuse, whereas the GPS measures the speed along the adjacent. The bigger the angle between them, the bigger the error.
Checking on a flat road is not an issue though.Mark.
2006, D3 SE Auto - gone but not forgotten.
2014 BMW 530d M Sport Tourer.
1977 Triumph Spitfire 1500
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22nd Apr 2010 4:58 am
Winger Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
If you have Sat Nav on your Discovery, you can check the GPS speed via the diagnostic screen.
22nd Apr 2010 6:38 am
wobbly
Member Since: 25 Feb 2010
Location: Zumerzet
Posts: 50
The gps was checked along a flat straight road to avoid this very issue.
I havent used the on-board gps yet - only because the roadangel has itself been calibrated using a calibrated speedo (which in turn has regular checks etc) and it is known to be accurate, whereas I havent yet checked the calibration of the LR system and probably wont as it will be accurate enough for car navigation.
I will be taking it out today to check the calibration on the odometer - there is a 'measured mile' used by Police near to us - I expect it to be correct based on the post above by Winger, but I want to confirm this physically against known quantities.
Too much time on my hands....
PeteMay the road rise with you.
May the wind always blow at your back.
And the sun always shine on your face.
May God always hold you in the palm of his hand.
22nd Apr 2010 7:43 am
Winger Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
I should have added that you can compare the GPS speed with the MOST speed (which is was the speedo uses as its reference).
22nd Apr 2010 8:12 am
daimlermg
Member Since: 31 Jan 2010
Location: N Yorks
Posts: 140
I want to check my speed and MPG this way but my diagnostic screen will not show. I have pressed in the right places and the dealer was unable t make it work.
Is it possable to enable and disable it in the CCF file and if so can you guid me to the right setting please.
I have a MSV-2.
TIAFaultmate MSV-2
500,000 plus miles in RR,s and trying for more without breakdowns this time
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22nd Apr 2010 9:42 pm
baconbutty
Member Since: 28 Mar 2010
Location: N Yorks
Posts: 34
Fuel economy improved dramatically as it is now on the back of a recovery truck somewhere in France! Engine Sytem Fault says the dash. Nice french mechanic picked me up and quipped 'ah, so zat is vhy zay call zem Land Rover Recoveries eh'
24th Apr 2010 5:04 pm
Russell
Member Since: 23 Aug 2007
Location: Kent
Posts: 10564
baconbutty bad luck, have you been given a loaner? If so what did you get, or are they bringing you home.MY17 D5 1st Edition Namib Orange
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24th Apr 2010 6:09 pm
baconbutty
Member Since: 28 Mar 2010
Location: N Yorks
Posts: 34
Land Rover Recovery were excellent. The car was recovered within an hour and a half and we were in a rental car (ok only a Citroen Picasso) but we were on our way. Changed this at Calais for a UK Vauxhall Insignificant and we got home. Going to post elsewhere but now wondering what to do as I need a 4x4 and need a tow bar. Recovery guys told me 4x4 maybe but no tow bar possible. Guess LR Customer Care best port of call?
26th Apr 2010 6:32 am
jwblue
Member Since: 19 Sep 2008
Location: On the sand
Posts: 22
Are we still talking about an LR4? The advertised MPG for LR4s in the States is 12 city/17 highway.
I have never seen a vehicle here in the States go above the advertised MPG as much as people are getting in this thread.
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