Accuracy of in-car computers

bwg11, Oct 17, 4:08am
Just wondering, I read some rather fantastic figures being quoted on the MB. Has anyone checked actual fuel used or just quote the read-out from the computer!

My wife's new Swift Sport shows a lifetime consumption of 14.7 kms/litre, whereas in fact it is only doing 12.5 kms/litre. This is from 400 kms to 3000 kms.
kcf, Oct 17, 4:10am
I don't have a computer so I just compare trip meter, to the fuel pump when I'm filling up.
a.woodrow, Oct 17, 4:12am
I've checked mine against fuel used and always found it to be very accurate.
smac, Oct 17, 4:20am
Mine is within a couple of points (i.e. might show 8.4l/100km but calculated is 8.5). 'Fuel used' was reading about 1litre low over a couple of tanks, so about 1% error. Km's travelled are within about 3%.

Shows an average of 8.5l/100km over the last 3000km (FG Falcon G6E).
a.woodrow, Oct 17, 4:23am
Has the tyre profile on the swift been changed!

snap sr2!
bwg11, Oct 17, 4:37am
Good thinking1, thought you both might have been onto something, but I have just checked the standard Swift's 175/65 x 15 against the Sports's 195/45 x 17's but the difference is only 0.2%
clark20, Oct 17, 4:47am
And how acurate is the Odometer!
bwg11, Oct 17, 4:53am
Good point. I will have to check it.
thejazzpianoma, Oct 17, 6:23am
Aside from the accuracy of the computer its worth noting that there is a real divide in terms of fuel efficient technology between many of the cars on the road at the moment.

You have some camps going the whole hog with fuel efficient automated manuals (Ford, VW etc) and coupling that with amazingly efficient technologies like direct injection and lots of other little measures like electric power steering that all add up.

Then on the other side of the coin, you have some surprisingly popular vehicles that have just enough kit to make them heavy like other modern cars (air bags, safety cells, larger bodies etc) yet are still using standard engine and drivetrain technology from 20 years ago.

I think a lot of people driving those sorts of vehicles (and I am not having a go at you here) just don't grasp how far ahead we have come.
berg, Oct 17, 7:55am
Could be onto something here as our Swift Sport reads 10% fast throughout the speed range.
berg, Oct 17, 7:57am
Yep even the Swift has electronicpower steer Jazz
pauldw, Oct 17, 8:41am
I have an SX4, on a trip of 120km there's less than 0.5km diff between odometer and a Google Track log. Speedo reads fast but not even 10% across range 54 ind = 50 real, 104 ind =100 real.
thejazzpianoma, Oct 17, 8:08pm
Its a step in the right direction, they could use more little economy improvements though, its a bit like weight reduction, every little bit helps.

The move to CVT is another good one though, just a shame I think they have chosen one without a replaceable filter.

Oh and I wasn't necessarily having a direct go at the Swift, just more in general.

Here's a silly stat for your amusement. Apparently electric power steering gives you an equivalent fuel savings as a 50KG weight reduction. (if I remember rightly)
raymond00001, Oct 17, 8:37pm
Put 860000km on a R580 Scania and a big fan of these computers. Would always reset the trip computer when refueling (a habit frommotorcycle riding) and it would be accurate to within +/- 5 Litres when filling up say 250-280 litres at next stop. Thats a 2% accuracy margin or better.
Great when your doing an unfamiliar route as you can estimate your range by the current instantaneous reading of litres/100km usage.
Great to see when someone has been thrashing your gear and brings it back with the fuel economy showing a 25% or worse reading than what you can do the job in.
chebry, Oct 17, 9:01pm
Its hard to match fuel comsumption figures like that a minor difference in shift points can eat a lot of fuel, I was quite happy to get 1.9 against 2 km L in a Volvo I drove recently Napier-Hamilton return hills suck fuel and leaving the computer to make the gear shift decisions does not save fuel it goes too early and takes too many gears.