Vistalite
Totally Hooked
I suspect that the figures being quoted from the dash display are not to be fully relied upon and the more accurate method is tank full to tank full and establish the volume used from the distance travelled.
Time to throw a cat among the pigeons.
The dash display calculates the average MPG by simply checking how much fuel has been used, over over a set distance, presumably the same distance as is recorded in the trip computer.
Everyone says this is not accurate, and that instead the only accurate way to calculate your fuel usage is by taking note of how much fuel you put in after a fill up to the brim, and then dividing that by.....the distance travelled in the trip computer.
Why is is that we universally agree that the car's trip computer is not reliable enough for method one to be accurate, yet is somehow reliable enough for us to make method two accurate?
Not saying you are wrong, by the way. I do it that way too. It just occurred to me recently that we all do this, claim the car's computer is inaccurate, and then use another method which relies on figures provided by the exact same computer
I guess the claim is that brimming the tank is somehow a more reliable way of measuring how much fuel has been used between fill-ups. But there seems to be enough variables which affect the fuel cut off at the pump (sometimes the pump cuts off if you hold it at a slightly wrong angle) that I can't see how it's considered more accurate than the car's ECU, which presumably knows precisely how much fuel is passing through the injectors every second.Would welcome any engineering input on this.
Distance travelled isn't the hard thing to calculate. Fuel used is. The control of how much to inject isn't likely to be logged - probably isn't even measured by volume. And then there's adjustments they may make for physiological benefits. If you use same pump and angle then brim to brim is pretty accurate - especially when averaged.
Oh. I would have thought that any remotely modern car with an injection system would measure this quite precisely in order to be able to adjust fuel mixture for emissions and stuff. Fair enough.
The thing is, I'm less bothered about economy nowadays. I used to religiously check it after every fill up (manual method). Now, I check it every so often and take an average between that check and what the dash MPG shows. But really, I'm only really concerned about the trend, economy is going up or down, and that's easier to see with the dash display, even if the figure is 1MPG out.
midlife_sportscar
Totally Hooked
It's done more by injector time, and correction by monitoring the combustion via lambda sensor - the fuel volume will be calculated.
That calculation will have a, hopefully small, error, but cumulative over the many injection cycles.
Vistalite
Totally Hooked
I hope I haven't set the cat among the pigeons? I am old school and prefer to deal in physical amounts rather than relying on software.
I questioned it on account of a recent trip I made in the car to Cardiff this week, which according to the dash display suggested it was achieving over 41 mpg which I find difficult to accept
I questioned it on account of a recent trip I made in the car to Cardiff this week, which according to the dash display suggested it was achieving over 41 mpg which I find difficult to accept
Yeah , the auto gearbox gives much better mpg.
A year back I brimmed the tank set the trip and reset the MPG and then compared the two methods and it came out identical and I do mean identical not near enough. After that I just relied on the recorded MPG. Had a new 440 BMW for a day and clocked 150 miles and it was horrific on fuel yet there always people on line saying they get 40 on a run. Put what a I thought was enough fuel in for the day about 60 miles from home realized it need topping up put what I thought was more than enough and had to stop again all below 80 dual carriagway and motorway. Made the GR86 seem super economical.
Silver Fox
Totally Hooked
- May 7, 2022
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Weight.
Not sure which one you had, but a quick Google reveals that the current M440i Coupe xDrive or whatever it's called is 1,810 kg. Which is f**king ridiculous.
In terms of my current mpg - I seem to be hovering around 37 mpg for mixed driving, and can get low 40s on a longer run. For example, a pleasant gentle cruise home from Caffeine & Machine this week (30 miles) with the windows down enjoying the cool evening air saw 41.2 mpg for the journey, which was nice.
midlife_sportscar
Totally Hooked
That's always going to be the most reliable way.I hope I haven't set the cat among the pigeons? I am old school and prefer to deal in physical amounts rather than relying on software.
I questioned it on account of a recent trip I made in the car to Cardiff this week, which according to the dash display suggested it was achieving over 41 mpg which I find difficult to accept
The dashboard average on mine is 30.9, and the measured average over the same period is 30.3 which seems pretty fair.
I had a 3.0 diesel about 15 years ago and the trip computer was OK under average conditions, but it wasn't linear - if you were getting high mpg it was very optimistic, but would under read low mpg. You could see anywhere between 25 and 45 but in reality it was probably 30 to 40, and at 35 it was about correct.
TorqueOfTheDevil
Obsessed member
Wait until you see how much the new M5 weighs
Silver Fox
Totally Hooked
- May 7, 2022
- 3,604
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If it's over two tons BMW can go eat a bag of d!cks.Wait until you see how much the new M5 weighs
*checks BMW website*
*orders huge sack of d!cks for BMW*
It was a 2023 version so yes current. When I get back from a short break I am going to see how many MPG I get if I really try if it’s not 40 I will have to hang up my string backed driving gloves
SJR202
Totally Hooked
The reason I think the mpg figures are overly optimistic as I don’t think it’s counting being stationary. Whenever you come to a stop the display goes to —— dashes which would to me suggest it’s not recording mpg when it’s effectively 0. Im consistently getting 32-33 on my commutes which is a mix of stationary traffic and slow moving, and accelerating quite hard out of roundabouts. It feels even an ecomonimcal petrol car would struggle with those figures day to day
Have now done just over 3k miles, working out the mileage on each tank full, tend to get in the 28-29 region. But most of the driving is ‘fun’!
Having only recently realised how to re-set the display mpg, today had 41.7 when going from home to office along A roads in traffic.
Things were better on the journey from that office to the one I’m based at, which are along very nice Welsh ‘B’ roads, that part of the journey was showing 21.5mpg (but with a much higher ‘smiles per mile’ ratio!!)
Having only recently realised how to re-set the display mpg, today had 41.7 when going from home to office along A roads in traffic.
Things were better on the journey from that office to the one I’m based at, which are along very nice Welsh ‘B’ roads, that part of the journey was showing 21.5mpg
(but with a much higher ‘smiles per mile’ ratio!!)
Silver Fox
Totally Hooked
- May 7, 2022
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140-odd mile trip to the coast, mixed roads mostly smooth flowing at or near to NSL, occasional bursts of enthusiasm tempered by the tut-generating fun sponge in the passenger seat.
A frankly almost unbelievable 39.7 mpg.
A frankly almost unbelievable 39.7 mpg.
CPH6R
Devoted member
Biggest worry in purchasing was that car would drink fuel when not in fun mode, So after first 7000km I have averaged 6.9l per 100kms or 40.9MPG! (per the trip computer), Not sure if this is something to be proud of or ashamed of!
That has involved some massive trips from Sweden to U.K. and U.K to mid Spain. When driving very long distances I have always adopted a 'minimise effort' approach - it is just much less tiring to sit behind an HGV for a bit vs battling traffic. So these trips I guess spanned 80kph (German roadworks speed limit) back up to a normal 110kph cruise. I have also had some fun in the mountains of Northern Spain so not all motorway / boring stuff. Anyhow wallet pleased! I am going to tick the top button in the survey now.....
That has involved some massive trips from Sweden to U.K. and U.K to mid Spain. When driving very long distances I have always adopted a 'minimise effort' approach - it is just much less tiring to sit behind an HGV for a bit vs battling traffic. So these trips I guess spanned 80kph (German roadworks speed limit) back up to a normal 110kph cruise. I have also had some fun in the mountains of Northern Spain so not all motorway / boring stuff. Anyhow wallet pleased! I am going to tick the top button in the survey now.....
midlife_sportscar
Totally Hooked
I went to York and back (from Manchester) last week - steady away, nothing special, but it pushed the tank average up from the typical 31mpg to about 36.
With some dodgy maths, I reckon I averaged about 38 for the trip, which I think is pretty good.
I filled up with 13 miles remaining according to the car (the light came on at 19) but it still only took 42 litres after covering about 330 miles.
With some dodgy maths, I reckon I averaged about 38 for the trip, which I think is pretty good.
I filled up with 13 miles remaining according to the car (the light came on at 19) but it still only took 42 litres after covering about 330 miles.
TorqueOfTheDevil
Obsessed member
I'm off on a 4 hour round trip to Ashford later... Bringing my dad and sister so taking the V8 Hilux..
Might get 20 if I behave
Might get 20 if I behave
