Thread: First tank of gas in the Diesel

Originally Posted by BrianElloy

Scott is this true? Reason I ask is that it’s a known fact that the speedometer is optimistic by 4-6km/h at 100km/h on stock diameter tyres and as time is a constant the variable must be distance

I found that when I had my 265/65R18 K02’s the accuracy between GPS and speedo was almost dead-on

Now that I’m back to 265/60R18 I’m back in the 4-5 km/hr variance again

Ergo if the Speedo’s are optimistic then so must be the ODO (ie reading more than actually covered)

My humble $0.02

The speedo is not necessarily on the same calibration as the odo. The odo is trying to read true but the speedo applies a fudge factor to this to purposely read high. The factory setting is +3%+2km/h if I recall correctly? You can change it in the CCF.

I understand you can adjust the odo calibration in the CCF also if you change tyre diameter.

Cheers, Chris.

It’s as Chris says, odometer and speedo are not the same. By law the odometer is required to be accurate and the speedo is required to never read too high. Most manufacturers apply a factor to the speedo readout to ensure compliance. The fuel economy readout being optimistic is an LR oddity. All these things have parameters in the CCF however IIRC correcting the speedo has proven difficult for some reason, there has been posts on it.

Scott

I just learned something!

Originally Posted by loanrangie

Stock size tyres ?, don't think a GPS would account for climbing/descending etc on different terrain.

Yes you may be right about the tyres as the ones I have now have 40mm greater circumference than standard but that amount is a minimal change. I reckon the only number that you can trust when doing fuel calcs is the litres used as this is from a pump that has to be tested by an authority so you'd hope it's right. Some may doubt this though. Many others here have mentioned that the speedo doesn't read true speed by varying amounts and my own test show me that the distance differs from GPS (yes, slope is not taken into account) so I guess what I'm suggesting is that anything read off the instrument panel is a (rough) guide only.

Originally Posted by cjc_td5

The fuel usage readout on the dash also appears to be a rolling average (don't know over what interval though), not a reading for that particular tankfull or from last reset.

Good point I've noticed this. I estimated the interval was around every 100km. Was judging by driving conditions vs. Speedo change though so just guessing really.

Definitely zero correlation between resetting the trip and the provided l/100km consumption read out. Other than they both reset at the same time.