Fuel consumption / economy report

[the evil twin]

I was thinking the fuel usage jumped when I put the chip on it but I just realised I put it on the same day the 33s went on so that might be the reason for the fuel increase ? I think standard tyres are 31" ? I remember they were road tyres & looked like they were off a commodore


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Larger dia tyres will use more fuel... but... don't forget you will now travel further than your Odo thinks you have.
If you haven't already done so you will need to check your Odo calibration and use a fiddle factor in your distance travelled.
Note that your Odo error may possibly be significantly different to your Speedo error.

[Sprock]

Yeah that's what I would've thought so I checked the speedo against my GPS speed reading & it didn't seem change ? I expected it to as the difference between new & worn tyres on the drive of the truck is about 3-4kmh ... I'll do some more testing as I was more excited about putting the chip on it at the time .


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[threedogs]

32" in a AT build with a HWY pattern is closest to OE
I lot here get very good return running 265s/32"x 10.5"
down into single figures for some. I run a 11.5" x 33" [mud]
and get about 13-15/100k depending, speedo is consistant with the GPS

[the evil twin]

Yeah that's what I would've thought so I checked the speedo against my GPS speed reading & it didn't seem change ? I expected it to as the difference between new & worn tyres on the drive of the truck is about 3-4kmh ... I'll do some more testing as I was more excited about putting the chip on it at the time .


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As posted you can't necessarily go by the speedo reading error

Speedos are required by law to be dead accurate or overread ex factory but not so the Odo's
Speedo will normally overread a tad ex factory and going to 33's usually gets them very close to actual
Odos are usually very close ex factory and 33's will get them to underread a tad

Definitely not always the case but more often than not in my experience

[Sprock]

Rito mate thanks


2002 GU wagon 3.0lt , auto , piranha dual batteries , 3" lift , chip , needle & Dawes valves - just gettin started

[Sprock]

As posted you can't necessarily go by the speedo reading error

Speedos are required by law to be dead accurate or overread ex factory but not so the Odo's
Speedo will normally overread a tad ex factory and going to 33's usually gets them very close to actual
Odos are usually very close ex factory and 33's will get them to underread a tad

Definitely not always the case but more often than not in my experience

When you say 'a tad ' how much do you reckon ? Roughly ? ie; 1000kms on odometer would be .......1050kms ? Or not that much ?


2002 GU wagon 3.0lt , auto , piranha dual batteries , 3" lift , chip , needle & Dawes valves - just gettin started

[BigRAWesty]

When you say 'a tad ' how much do you reckon ? Roughly ? ie; 1000kms on odometer would be .......1050kms ? Or not that much ?


2002 GU wagon 3.0lt , auto , piranha dual batteries , 3" lift , chip , needle & Dawes valves - just gettin started

Well when I went from 31" to 33" my speedo went from being 8k behind at 100km/h to smack on 1-1 with the GPS. .
When I was coming home from the farm (about 600k) my odometer was about 40k short of the distance traveled via GPS. .
So it can be a fair bit..

[Sprock]

Rito Westy thanks mate


2002 GU wagon 3.0lt , auto , piranha dual batteries , 3" lift , chip , needle & Dawes valves - just gettin started

[threedogs]

Same as Kallen ,,,,, I heard vehicle manfacturers were allowed 10% error in speedo readings.
Get a speeding ticket they only give you 3% error funny eh

[the evil twin]

Agree with Westy... Once you 'know' your errors it is a lot easier and you only need to sort it out once
The Odo to Speedo relationship can be up to 10% or more and won't change with tyres, diffs etc

Lets assume (rough figures for example only)...
The Speedo indicated to actual is out, say 7%, and reads 107 at 100 actual and you then increase the tyre size by say 7% (31's to 33's) it will now be spot on
The Odo indicated to actual is out, say 1%, and reads 101 for 100 K's travelled and you then increase the tyre size by say 7% (31's to 33's) it will now read 94 K's for every 100 travelled
If you change the size of the tyres by another 7% ish (33's to 35's) the errors will change by the same percentage
If you change the diff ratios by 5% ish by going from say 4.3 to 4.1 the errors will change by the same percentage