Mpg

[Shugster]

Drove 20 miles this morning. Mixture of motorway and B roads. No mode selected.

Computer saying I averaged 72.4 mpg.

Couldn't believe it as wasn't trying to be economical just driving as normal. 😀

Hope computer correct as did not imagine I would ever achieve these figures. 😳

[Parts-King]

It is entirely possible to get those figures BUT it will depend on a lot of factors, and you have only done it over a very short distance

You need to be checking it from fill to fill, my average overall was high 50's in a Prius but that included winter driving too which hits the Prius hard

Kingo

[Shugster]

I know.

Was just delighted to achieve this with so little effort. Especially as motorway driving in high 60s and busy B roads.

[theoilburner]

That's impressive. On a single journey we managed 65 mpg once, the overall average on ours is 56 mpg over 2000 miles. 70 mpg would be something else!

[Ten Ninety]

A mere 72.4? Pah, I give you 92.5!

Unlike you, however, I was trying - as you can see from the graph I try quite a lot! At least you achieved your 72.4 without really making an effort, which must give you bonus points for nonchalance.

[Dasbob]

My PB is 82mpg over 25 miles.... it all depends on so many factors, i suspect the alignment of the stars plays a big role... i did discover after filling up i lost about 15% on my average mpg for that load of fuel :(... just to warn ya

[Shugster]

Jings Crivens!

I must really be a beginner.

Looks like I've got a long way to go.

[johalareewi]

Wind is a big factor (and gravity). Downhill with the wind behind you is the way to go

[Opifex]

A mere 72.4? Pah, I give you 92.5!

Unlike you, however, I was trying - as you can see from the graph I try quite a lot! At least you achieved your 72.4 without really making an effort, which must give you bonus points for nonchalance.

A mere 92.5? Pah, I give you 99.9!

II wasn't trying - just driving down a very long hill.

My best real life mpg was 80mpg - ideal conditions - 50 miles of flat road, warm afternoon, little other traffic, steady 50mph cruise through beautiful countryside.

My average is 55.2mpg over 30,000 miles in three years including a lot of fast French motorway.

[Ten Ninety]

Heh, I thought someone would have a 99.9 image somewhere! :D

My 92.5 was over 29 miles but it was a bit of a cheat as the car had fully warmed up before I filled up with petrol and reset the meter. There was definitely some tailwind involved as well, I think, because I've done the same route several times since and not gone past 85. That's all measured on the display of course, which I find is usually 5-7% optimistic.

It does sometimes feel like the 'alignment of the stars' has an impact; there are days when it seems easier to reach a particular figure despite taking the same route and driving in what I think is the same way. In reality I suspect it's all down to the wind, temperature, wet roads, tyre pressure and the behaviour of other traffic.

However, I have noticed a curious phenomenon regarding engagement of 'milkfloat mode' - there are some days where the car temporarily refuses to drop onto Battery power despite the indicator showing sufficient charge and the speed being appropriately low. This happens in both the wife's Auris and my Prius, so it's clearly by design. However, somewhat freakishly, it only occurs at three specific locations on my commute, and then only maybe one day out of ten. It happens on cold mornings and hot afternoons, so doesn't seem to be related to temperature. I guess it's something to do with Battery conditioning, but it does knock the mpg down a bit when it happens.

[Cirsium]

Sorry to be miserable git but the indicated mpg is usually too high (=garbage). You need to measure it and over at least 100 miles ideally 200 or the errors of measurement are just too great.

[theoilburner]

Oh, you spoil all our fun! :) Last time I brimmed the Prius I found it optimistic by 2%, so not so bad. The C4 GP we had before that was optimistic by at least 10%!

[sanzomat]

I'm finding the displayed mpg to be around 6% optimistic based on a tank full. (albeit after only three fill ups but has been consistently 6%). This makes it the most accurate trip computer of all the cars I've ever owned. For the record most (including Ford, Renault, Vauxhall and Volvo) have been around 10% optimistic and the worst goes to the Audi A6 which was consistently over claiming its mpg by around 16%. It nearly always said I'd achieved around 46mpg but when I worked it out on the miles travelled and fuel used it was usually only 39. The other factor that I've not yet checked is how accurate the odometer is as this can obviously affect the "actual" consumption figure but is hard to allow for as you can't do much but use the figure the odometer records. For interest, the journey from my home to the Hammersmith flyover was exactly 100 miles dead in my Volvo V70 but in a Mondeo the same journey had grown to 105 miles! Assuming odometers work on the number of rotations of a wheel you also need to factor in how worn your tyres are - a tyre on the legal limit will turn about 2% more times over the same distance as a brand new tyre due to the diameter shrinking by around 12.5mm (diameter of a 205/60/16 tyre is around 650mm)

[Parts-King]

I find it amazing that people expect the display to be 100% accurate!

There has to be an inbuilt variable to allow for all of points mentioned by sanzomat. I have found it to be within 5-10% of just about every car ive driven (and there have been hundreds in 30 odd years of company cars) and that will do for me!

Kingo

[Cirsium]

There is a calibration command to allow for new tyres on my T Spirit July 2013. I agree about the optimistic readings but even if the readings had zero optimism you can't measure an accurate mpg using small inputs without big errors. Mine gave a displayed 72 mpg reading today on about 100 miles - I don't really believe it but haven't had time to cross-check using pump volumes and odometer readings.

[timberwolf]

There isn't a device built into the car that directly measures how much fuel has been consumed - AIUI the quantity of petrol used has to be estimated from the operation of the engine, some sensors in the engine operate as feedback loops rather than give a specific value so can't be used. I've always wondered what they use - timing of the injectors maybe, some indirect sensor reading that they know has some correlation with fuel consumed?

[valmiki]

One thing I have noticed is that the mpg indicator tends to be more accurate during the warmer weather, for some reason the cold weather puts it out of kilter even further.