"True speed"?  No such animal.  Some relevant info here: http://www.briskoda.net/forums/topic/103487-true-speed-display-with-columbus-gps/?hl=%2Bsatnav+%2Bmph#entry2410939

 

why dont we put up a post showing how to work it out correctly?

that way people like me who drive  very economically can once again wind everyone else up!

Fill up.  Note mileage and quantity of fuel.

Drive.

Fill up.  Note mileage and quantity of fuel.

Drive.

Etc.

Fuel consumption = miles driven divided by fuel used.  (Gallons = litres x 2.2)

How simple do you want it?
 

.

So?  The mileometer on my Octavia is just as accurate the the mileometer on any other car I've ownerd - they all read the same over the same journey.

 

 

really?

 

my Dad used to drive ~175 miles between Ayrshire and Aberdeen for his work for about 2 years. Same route every time. He noticed that the journey was apparently shorter by a few miles when he moved from "near the limit" worn tyres to using brand new "lots of tread" ones.

Fuel consumption = miles driven divided by fuel used.  (Gallons = litres x 2.2)

How simple do you want it?

 

 

Well, I suppose I'd want it right for a start:

 

 

As 1 gallon = 4.546 litres your equation ends up as follows.....

 

4.546 litres x 2.2 = 10 gallons (nowhere near 1 gallon)

 

Or

 

1 litre x 2.2 = 2.2 gallons (really?)

 

 

Try 0.22 and maybe you'll start to make a bit more sense.

 

 

(1 litre = 0.2199 gallons)

ok so here I go,

 

over 3 fills all of which total to 153Litres I managed 1827 miles.

 

so if my math is correct

 

153litres / 4.546= 33.65 gallons

 

1827 miles / 33.65 = 54.29MPG????

 

am I correct ?

just for reference, my mpg on maxidot reads 1) 50.7mpg 2)52.03

 

the second one hardly changes day to day but the first seams to be real time.

just for reference, my mpg on maxidot reads 1) 50.7mpg 2)52.03

 

the second one hardly changes day to day but the first seams to be real time.

 

"2" is since you last reset it (holding OK until it resets or battery disconnect) regardless of what happens after the reset.

 

"1" is more a journey indicator. It will auto-reset when you haven't used the car for 2 hours. (or you manually reset it).

 

So, in your case, MaxiDot would appear to be under-reading by approx 4%.

This can be corrected with VCDS, but again, I would make sure the speedo is as close to calibrated as possible first. The other upshot of speedo calibration is servicing. As the speedo over-reads, the car will think it has gone further than it actually has. If the Speedo is out by 2% it would mean {not an unreasonable figure} you'll come in for servicing (if you're on a 10k service regime) 200 miles earlier. Whilst is could be argued that 200 miles is neither here nor there in the overall scheme of things, IMHO is seems silly to go through all the effort of trying to save money, only to lose it on having the car serviced earlier. Over 100,000 miles, the car would have been in 2000 miles earlier, which is two months of driving for me. Getting another two months over the servicing life is a reasonable saving, IMHO.

Sniff!

Trip 2 auto re-sets after 20 Hrs or somesuch otherwise arbitary limit.

It definately does NOT continue "ad infinitum"

cheers

m

ok so here I go,

 

over 3 fills all of which total to 153Litres I managed 1827 miles.

 

so if my math is correct

 

153litres / 4.546= 33.65 gallons

 

1827 miles / 33.65 = 54.29MPG????

 

am I correct ?

.

Seems OK to me.  That wasn't difficult, was it?

Just two comments:

- I find it easier to multply litres by 0.22 than to divide by 4.546

- an mpg quoted to two decimal places suggests a probably spurious degree of precision.

I'd simply say you had been getting around 54 mpg.  If you feel like bothering, you could - if you really wanted to - calculate the mpg between each fill-up.  You might find that there is quite a variation, which will indicate the extent to which your mpg varies.

Have a read of my original post!  Between successive fill-ups, my fuel consumption was 39.01, 42.05, 41.26, 41.07, 43.23, 42.13, 42.03 and 42.88mpg.  The overall overage was 41.76 but I find it far more sensible simply to say that most of the time my mpg is between 41 and 43 mpg.

Apart from anything else, remember that you usually only note your mileage to the nearest whole mile, the pump only indicates to the nearest 0.01 litre and there are other random and systematic errors in the data - as well as the fact that you get less fuel in warm weather.  So don't get hypnotised by apparent (and irrelevant) differences of 0.01 mpg.

Even just stating the fuel consumption to the nearest whole number is sufficient for me to be aware that

- the dashboard computer on my Octavia is way out (42mpg compared with 50mpg - around 14%)

- there was a significant difference between two supposedly identcal citroen BXs I had (47mpg compared with 53mpg  - around 9%)

   

Edited 29 April, 201412 yr by Stuarted

Sniff!

Trip 2 auto re-sets after 20 Hrs or somesuch otherwise arbitary limit.

It definately does NOT continue "ad infinitum"

cheers

m

 

From the handbook.....

 

Single-trip memory (memory 1)

The single-trip memory collates the driving information from the moment the ignition

is switched on until it is switched off. New data will also flow into the calculation

of the current driving information if the trip is continued within 2 hours after

switching off the ignition. The memory will be is automatically erased, on the other

hand, if the trip is interrupted for more than 2 hours.

Total-trip memory (memory 2)

The total distance driven memory gathers data from any number of individual journeys

up to a total of 99 hours and 59 minutes driving or 9.999 kilometres driven.

The memory is deleted when either of these limits is reached and the calculation

starts from anew.

The total-trip memory will not, contrary to the single-trip memory, be deleted after

a period of interruption of driving of 2 hours.

 

 

.....maybe yours is broken?

That's what I'm asking. So knowing that my speedo "under reads" then it would be plausible that someone could travel faster and argue that fact to get out of a speeding ticket. I mean I'm not overly concerned I usually just go up to speedo 70 and switch on CC but if at 70 there's a 5-6mph discrepancy then obviously another car would be travelling at a different speed thinking they are doing 70. If that makes sense?

If you get pulled up and you know that your speedo was indicating over the limit you've got no defence. If they were permitted to under-read then that's a different story.

You're confusing under- and over-reading. It's illegal for a speedometer fitted to a car to indicate that you're travelling more slowly than you are.

Edited 29 April, 201412 yr by Mister Paul

Wow 9.999km, thats about 6.21309055 miles

ps

MINE'ZIZ def resets much sooner than 99hrs 59 mins

but not after 6.21309055 miles!!!

Hmmm. 400 miles from a tank means I'm not out of pocket on a business trip. 300 and I've been having fun. The on board computer is more than sufficiently accurate to gauge all points in between. If I was any more concerned about the accuracy, then I'd buy a prius (actually I wouldn't as they're not that great but you get the idea). Life's too short!

Sent from my ME301T using Tapatalk

However, FWIW yesterday's trip from Cardiff to Mansfield and back at 362 miles, filled up brim to brim with 10.15 gallons means a real average of 35.66 mpg. Computer said 34 ish on way up, 38.4 way back. Given the performance, I personally struggle to see the relevance of the vrs diesel, but of course there are many reasons why we choose cars, and thankfully we're not all the ame.

It's interesting to see that there is such a wide variation: some drivers (like like steve750 above) finding that, when they actually measure their fuel consumption, it closely matches what their computer says.  Whereas others (like me) find that there is a massive and consistent discrepancy.

Seems to show that if you have any interest at all in your fuel consumption, it is worth (even if only occasionally) actually measuring it, properly - fill, note mileage, drive, fill, note mileage and quantity of fuel needed.

Just in case anyone needs a reminder: (end mileage - start mileage) / (litres x 0.22) = mpg

Being a miserable, tight-fisted old git as well as a bit of a sad Anorak, I knocked up a simple spreadsheet into which (from time to time) I enter these details, having noted mileage & fuel in my diary each time I fill up.  I suppose you could write these on the back of each fuel receit if you preferred.

This spreadsheet (which of course does all the arithmetic and conversion for me) then shows me at a glance the overall fuel consumption as well as the fuel consumption between each fill-up.  This latter figure is useful because it shows the extent to which my mpg varies, and stops me thinking that there is any point in calculating overall average fuel consumption to umpteen decimal places.  See the figures I posted earlier for an illustration of this point!

 

The Fuelly app / website can do all of this, and some. It's a geek's paradise

 

(though I admit to using an excel sheet to make up a rank/weighted analysis when choosing a car, and always end up ignoring the logical result and go with what I feel I want).

Thought id work out my weeks useage...PD105 BXE Elegance Estate.

Filled up, did 147 miles, filled up again.

The car shows 44.7 for that distance, calculated as 40.21 (16.62 litres of Shell V-Power Nitro+, which has been used for the last 2 tanks)

Back to Tesco for me!