|
Apologies if this has been already discussed. What is the accuracy of the trip computers many cars now have, especially in regard to mpg? I once asked HJ this, and he fired back an email on how to work out mpg by brimming the tank etc. But that is not really my question. I wonder if anyone has ever researched the general accuracy of these gadgets, otherwise what is to stop manufacturers setting them to give us the impression that their cars are doing better mpg on screen than in reality?
|
You can check your own by travelling a known distance on a motorway, determined by counting the little posts which are at known distances (I think 200 metres, but someone here will know). Make the distance as long as possible to reduce the error.
Alternatively some towns (Blackpool has one on Lytham road) have a measured mile, used for checking taxi meters.
|
|
|
Accuracy (mpg) of trip computer
The true mpg shown by mine is 10% less than the computer indicates. As measured by filling beyond the full mark and then zeroing the miles reading when the gauge falls back to the full mark.
Then I run the car until the tank is about a quarter full. Then I over-fill it again, noting the amount. Then I read the miles done for that quantity as those shown when the fuel gauge has dropped back to the full mark again.
Inaccuracy in the milometer as to distance travelled is not taken into account. But without using satelite equipment to work out the miles travelled, it is about the best that can be done.
|
Unless you put aftermarket alloys on, I don't see how it could be all that inaccurate. Does it not just measure each revolution of the wheels?
On a contradictory note, wasn't there some big hoohah with the 307 whereby for every 100 miles it did, it said it had done 125 or something like that?
--
Adam
|
|
|
Just a bit of pedantic nit-picking. I'm not sure GPS is all that accurate on distance. Doesn't it log distance as a straight line between sampling points, regardless of the course followed? Fine in a boat or aircraft, following a straight-line course, but less so for a vehicle on winding roads or a motorway with long curves. And what is the effect of altitude change and gradient in this case?
The effect may in practice be insignificant. Is it?
|
GP does measure distance by sampling points. On good ones (or good software) you can choose very short sampling points so get good distance calculations.
Back to the thread, Goona 2 - Trip computer is up to 10% inacurate with regard to fuel consumption, and very accurate with regards to distance as far as I can tell when checking with GPS and kilometre posts on the motorway (they are every 100 metres numbered in 10ths and kilometres).
|
Get a sharpish eyed passenger to have a look at the numbers on a marker post on the motorway, it'll be something like 29 on the top line and 9 on the next line. That signifies you are 29.9Km from some arbitrary (to you) point. Reset your trip computer at this point. Drive for a bit (as far as possible, really). Don't worry about not changing lanes, etc, just drive naturally.
Then, just at the point when you'll be leaving the motorway (or getting onto a different one) get your passenger to note the number on a passing marker post while you note the mileage on the trip computer. Then:
Subtract the smaller Km figure from the bigger. This gives you the total Km covered. Multiply this by 0.6214 to convert to miles. Compare this to the miles shown on the trip computer, then come back to us and tell us if you've found a discrepancy - we'd be interetsed to know.
Cheers,
V
|
|
|
|
|
|
My Octavia's actual mpg checking on refills is 10% worse than the trip computer. It would consistently report 51-52mpg, but at the pump i know i'm getting 46mpg.
|
|
|
Several threads on this already, check out 'Forum Search' on right.
In my experience, checking brim to brim mpg (using milometer distance), 97 Passat 110 TDi computer was 5% optimistic, 51 Laguna Sport Tourer 120 diesel 10% optimistic, 51 Golf 110bhp GT TDi (odd model for that year)is just 0.5%.
I suspect computer mpg accuracies vary as much as speedo mph's, though if I remember my childhood days of studying Autocar road tests correctly, milometer readings were usually much more accurate than speedos!
|
|
|
![2025 Volkswagen Caddy Maxi Life 2.0 TDI 122 Life 5dr DSG [Tech Pack]](http://images.honestjohn.co.uk/imagecache/url/crop/90x60/https/cdn.uk.prod.group-mobility-trader.com/images/cas/49d005ab3b4c612f2da96e77a369cf17/080e6fb3f727747306d8bb8220d3dda3.jpg)
![2025 Volkswagen Tayron 1.5 eTSI R-Line 5dr DSG7 [7 Seat]](http://images.honestjohn.co.uk/imagecache/url/crop/90x60/https/cdn.uk.prod.group-mobility-trader.com/images/cas/01c753dd15a6fdee5494198c0c39370b/5033c83c3060c4a815e03bf951275059.jpg)
