Fuel consumption (on-board comp vs. reality) ?

[pavproch]

Since 2013 I covered nearly 80 kkms with my Zet, enthusiasticaly, fuel consumption not my preference, always averaging 15 or 16 liters per 100kms until Tue/today. On Tuesday I fully filled the tank and covered approx 200kms afterwards "my ordinary style" (acceleration/brakes hard, redline often) and added today another hundred of the same, ie. totaling 300kms (onboard comp reading 16l/100km, but fuel still 1/3, not red as always after 300kms). Refilled anyway (preventively) = 36ltrs, ie. real consumption right at 12liters per 100kms.

During my 13years with Zet I sometimes registered slight disproportion between on-board comp and reality (but never more than one liter per 100kms), but today the difference reached full 4 liters (onboard 16 while real 12 only), wtf?

(Not any special fuel, just ordinary gasoline - our ident BA95NA - as ever = from premium CZ brand.)

Has anybody registered anything similar (ie. contradictory)?

 

[Rockhopper]

I don’t do litres (I’m in England) but my observations are that onboard computers are always at least a few mpg more optimistic that reality.

 

[Viper4]

Since 2013 I covered nearly 80 kkms with my Zet, enthusiasticaly, fuel consumption not my preference, always averaging 15 or 16 liters per 100kms until Tue/today. On Tuesday I fully filled the tank and covered approx 200kms afterwards "my ordinary style" (acceleration/brakes hard, redline often) and added today another hundred of the same, ie. totaling 300kms (onboard comp reading 16l/100km, but fuel still 1/3, not red as always after 300kms). Refilled anyway (preventively) = 36ltrs, ie. real consumption right at 12liters per 100kms.

During my 13years with Zet I sometimes registered slight disproportion between on-board comp and reality (but never more than one liter per 100kms), but today the difference reached full 4 liters (onboard 16 while real 12 only), wtf?

(Not any special fuel, just ordinary gasoline - our ident BA95NA - as ever = from premium CZ brand.)

Has anybody registered anything similar (ie. contradictory)?

I keep a spread sheet for my Z4 , and one of the things I analyse is the fuel consumption.

From the onboard computer my Average MPG shows 21.5 miles /gallon, and from my spreadsheet I am showing an ave of 21.0 mpg. Now the spreadsheet is based on the total fuel vs milage since I had the car. The car on board mpg average was reset after the first year.

For reference I went for a blast down to the coast today and my onboard comp showed 20.3MPG, at the start but this increased on the way down, but i was in normal mode and mainly slow B roads roads, on the way back I took fast A roads and motorways and did not spare the horses. Trip down took 2 hours, trip back took just over 1 hour, and in sport mode...nice

Average MPG after the trip increased from 20.3 to 21.5.

 

[pavproch]

I do not keep any fuel records but I am habitting to nulify daily ODO with each full tank, so it´s a very easy math whenever I do so at the gas station, always coming with the figures between 15 and 16 litres per 100kms (= 14 to 15 mpg), so this unique abberation of 12 l/100kms (=19mpg) cought my attention, obviously.