Fuel Consumption Figures

[figjam]

Way off topic ..... but the Victorian Gubbermint's addiction to income from traffic/speeding fines will have taken a big hit during the past, how many, months.
They are trying to make up that deficiency by handing out fines to people going for a stroll in places deemed out of allowable area.
How many of those fined are going to pay the fines ? Not many.
What are they going to do with the non-payers ? Chuck them all in jail. Cancel their licence. Cancel their rego. Crush their cars. Resume their house.
Victorians and visitors can look forward to even tighter traffic rule enforcement and larger fines, when the State gets back to a new normal.

 

[Badgerdog]

Ok I might have to eat my words here but in my magnum at a speedo reading of 53 the radar sign thingies that tell you your speed say 50 kph I presumed my speedo would read 106 at 100 kph but maybe I am wrong ? I will have to check with GPS

Its the weirdest thing isn't it !! The radar speed warning sign up the road from me tells me I am doing 50 and my speedo reading is 53 k.p.h.
Simple logic doubling that would suggest that if the speedo reads 106 the radar speed sign would read 100 but it doesn't, and it doesn't seem to matter if you're doing 7o-80 kph or any other speed, in my car its always a fixed 3 k.p.h. difference. Go figure ?

 

[Skylarking]

Its the weirdest thing isn't it !! The radar speed warning sign up the road from me tells me I am doing 50 and my speedo reading is 53 k.p.h.
Simple logic doubling that would suggest that if the speedo reads 106 the radar speed sign would read 100 but it doesn't, and it doesn't seem to matter if you're doing 7o-80 kph or any other speed, in my car its always a fixed 3 k.p.h. difference. Go figure ?

As you go faster, tyre diameter grows a little due to centrifugal forces so effective rear ended gearing changes. That means actual speed is higher than speed measured at gearbox when using old fashioned gear and cable type speedos... It also means that speed error doesn’t grow lineally with speed... But with electronic speed, one can make all sorts of compensation to what is displayed for any known error drift. This is the case whether one uses gearbox shaft speed or ABS wheel sensors to calculate speed as software is versatile and allows for much more control than cogs and cables...

The manufacturers could probably be accurate to 2 decimal places if they wanted to but that would require calibration at each tire change and periodically as tyres wear out... or they could use GPS to calculate speed... but ADR bind manufacturers into using earth bound systems (no gps) with defined error margins so in service a car can never display a slower speed than it’s actually travelling.

 

[stooge]

Its the weirdest thing isn't it !! The radar speed warning sign up the road from me tells me I am doing 50 and my speedo reading is 53 k.p.h.
Simple logic doubling that would suggest that if the speedo reads 106 the radar speed sign would read 100 but it doesn't, and it doesn't seem to matter if you're doing 7o-80 kph or any other speed, in my car its always a fixed 3 k.p.h. difference. Go figure ?

You will find that the programming is set to just display 3km less than the reported speed instead of it being some sort of percentage calculation so at 50, 100, 200 it is always 3 out.

 

[Badgerdog]

Thanks guys. I guess my old head is stuck back in the 1980's with silly old things like speedo cables lol

 

[Hq King]

Thanks guys. I guess my old head is stuck back in the 1980's with silly old things like speedo cables lol

Funny I have been setting cruise at 106 and have been driving by cops and speed cameras feeling confident that I am not speeding no tickets yet

 

[87VLCALAIS]

My RSV shows a consistent 2kph ± high. i.e at 100 indicated I'm doing 98 or at 50 I'm doing 48 by GPS.

 

[mirrabucca]

VX V6, but theory is the same. I upgraded the display on my VX (as most do...) and had the unit calibrated a the same time. The speed (digital) agrees with the GPS most of the time, but its only ever 1kph different and that is probably due to the GPS updating time. Trip distance and distance to go agree with the gps. On a side note, its great to go through fixed speed traps AT the speed limit, overtaking most other cars, and never getting a ticket!
I use the fuel consumed reading to work out which bowswer to fill up from. Consistently when the display shows (say) 47.3 litres used, the bowser will read up to 2 or 3 litres different. No big deal, but the same bowser shows the same error each time. I've had the car a long time. Lots of tankfuls, so it is consistent. Worth doing too. One pump at my local servo consistently says I got 4 litres less than the car's display said I needed. Week after week.
I dont often reset everything, go on a trip, then fill up and check, but when I do, the fuel consumption figures comparing bowser with car, agree, allowing for the discrepancy between bowsers. And there IS a discrepancy. Yes, I know the rules - I used to work in the industry, but there are differences between bowsers. Generally though, once you find a bowser, they usually are consistent day to day.
As far as I know, vehicles use injector timing to calculate fuel usage. So a clogged injector will have to stay open to supply the correct amount of fuel. So in theory, that car will show worse fuel consumption figures than it actually uses. As for calibration, yes, it can be done (again, in theory). Its a matter of finding a tuner who can do the work.