Fuel calcs

[tkn]

Decided to put this here because Ute/Tray Back section seems "unknown" - but it applies to all vehicles.

Fuel prices will get to $1.50 per litre (for real fuel, probably $0.85 for gas) pretty soon.
What follows might help you to reduce your fuel bills -
Say your vehicle is using 14L of fuel per 100km and usually its on road weight is 2400Kg (with all the stuff you carry around in it).
That translates as about 6 millilitres of fuel for each 1Kg that travels 100km
i.e. 14000 millilitres of fuel / 2400Kg = 5.83333 millilitres/Kg

Lets say an auxiliary battery weighs 20Kg, then to carry that battery 100km would use –
20 x 5.8333 = 116.67 millilitres of fuel.
If you travel 1000km with the battery, then it would be 10 x 116.67 = 1.167 Litres/1000km
If you average say 40000km per year, then 40 x 1.167 = 46.68 Litres p.a. to cart the battery around.
Which at current prices works out to be 46.68 x $1.30 = $60.68 p.a.
That might not seem like a lot, but if you carry 2 auxiliary batteries then it is costing you about $121 p.a. for the privilege.

This makes the calculation simpler –
U = Fuel usage per 100km (Litres)/GVM x Weight of Items x 1% of Distance travelled p.a.
e.g. using the 2 x battery figures above is 14/2400 x 40 x 40000/100 = 93.33
and Cost = U x fuel price per litre
e.g. 93.33 x $1.30 = $121.33

Now, in the real world, you can add up the weight of all the half Tonne of “extra stuff” in your vehicle and divide it into essentials like tools, winch, compressor, extra wheel, shackles, ropes, etc. AND all the other crap that somehow finds its way into your vehicle, then calculate what it is costing you each year to carry it around.
e.g. Essentials - 14/2400 x 200 x 40000/100 = 466.67 and 466.67 x $1.30 = $606.67 p.a.
Crap - 14/2400 x 300 x 40000/100 = 700 and 700 x $1.30 = $910 p.a.

If you are planning a trip of say 15000km with 600Kg of gear and where fuel stops are going to be few and far between, then reduce your fuel economy from say 14L/100km to 18L/100km (because you’re going to be fully loaded) and use the calculator to decide what to leave at home.
e.g. 18/3000 x 600 x 15000/100 = 540
AND 540 x $1.30 = $702.00 (which represents the additional cost of travelling with 600Kg of extra camping gear, food, clothes, etc.)

This does not include additional wear and tear on the vehicle and additional servicing costs – if you want to estimate that, then add 150%
e.g. $702 + $1053 = $1755.00 for your 15000km trip
If the roads are really rough, plenty of dust and mud, etc. double that figure e.g. $3500.00

[Bob]

You have just ruined my day. Knew fuel costs were high but i liked to put my head in the sand.

Having said that thankyou for your post which does put it all in perspective

[tkn]

You have just ruined my day

Sorry, Bob.

[Bigrig]

Top post mate, but you just killed everyone's plans of ever travelling again!!! LOL ...

Nice easy way to calculate the cost, only problem I can see is knowing the weight of said "crap". I know the weight of the truck, but wouldn't have the first clue about the weight once ladened with camping gear etc.

[MQ MAD]

14l/100Ks outta the TB42e

Where,where
Is there an economical version ???
(they average 20-25L/100Ks)

I look at it like this
IF ya want to drive a 3 tonne 4x4 (extra with add ons) with the aerodynamics of a block of flats
Economy isnt in the equation

I could run an XY GT 351 , with a tuff as nails 351 , that would get the same if not similar economy as my GQ
Now only to get the XY falc to do what the GQ can !!!

[the evil twin]

Uuummm I hate to be a wet blanket but there is a flaw in your logic.

I must say that I totally agree that removing weight WILL save fuel but the "weight" to "fuel used" ratio isn't a direct percentage like your equation as weight doesn't determine your fuel useage to a very great degree compared to other factors.

The variable amount of fuel required (as opposed the the set amount against drive losses etc) is determined predominantly by rolling friction and drag. The weight of the vehicle and its contents has no effect on drag so adding removing anything doesn't matter. Rolling friction is affected but the effect can be reduced but not nullified by appropriate tyre pressures.

Hypothetically, an example to illustrate. Two identical vehicles with a tare of 2200 KG do an identical trip of lets say 1000 K's. One has the Driver only so a GVM of 2300 (2200 plus 100) and lets say the other has Driver and 3 Pax and 400 Kg of gear so a GVM of 2200 plus 400 plus 400 which is 3000 or roughly 1/3rd more. Now I deliberately choose those figures because they are what we do a fair bit at work.

The heavier vehicle won't use anything like 30% more fuel indeed in a CRD the fuel useage would change by less than 1 litre per 100K's so it would use about 7% more at the max but willing to concede 10% (No way in real life I might add) for the sake of discussion but nothing like 30%.

In my Patrol (or the work vehicles) I would actually save more fuel if I took my roof rack off as drag is exponential so whilst I reduce weight as well the big saving is in reduced drag.

Again, I agree that taking weight out saves fuel, just saying the magnitude of the saving is much less than the formula so you might need to add another divisor of say 5 as a guesstimate as the $910 would be closer to $200 maybe $250.

We usually do Perth Carnarvon with Driver changes at 1/2 way Mill, Gerro and Billabong. The difference in fuel used between "two up and light on" and a "full vehicle around the GVM" when we gas up at Carnarvon at the end of the day is about 10 to 15 litres

[Bigrig]

Uuummm I hate to be a wet blanket but there is a flaw in your logic.

I must say that I totally agree that removing weight WILL save fuel but the "weight" to "fuel used" ratio isn't a direct percentage like your equation as weight doesn't determine your fuel useage to a very great degree compared to other factors.

The variable amount of fuel required (as opposed the the set amount against drive losses etc) is determined predominantly by rolling friction and drag. The weight of the vehicle and its contents has no effect on drag so adding removing anything doesn't matter. Rolling friction is affected but the effect can be reduced but not nullified by appropriate tyre pressures.

Hypothetically, an example to illustrate. Two identical vehicles with a tare of 2200 KG do an identical trip of lets say 1000 K's. One has the Driver only so a GVM of 2300 (2200 plus 100) and lets say the other has Driver and 3 Pax and 400 Kg of gear so a GVM of 2200 plus 400 plus 400 which is 3000 or roughly 1/3rd more. Now I deliberately choose those figures because they are what we do a fair bit at work.

The heavier vehicle won't use anything like 30% more fuel indeed in a CRD the fuel useage would change by less than 1 litre per 100K's so it would use about 7% more at the max but willing to concede 10% (No way in real life I might add) for the sake of discussion but nothing like 30%.

In my Patrol (or the work vehicles) I would actually save more fuel if I took my roof rack off as drag is exponential so whilst I reduce weight as well the big saving is in reduced drag.

Again, I agree that taking weight out saves fuel, just saying the magnitude of the saving is much less than the formula so you might need to add another divisor of say 5 as a guesstimate as the $910 would be closer to $200 maybe $250.

We usually do Perth Carnarvon with Driver changes at 1/2 way Mill, Gerro and Billabong. The difference in fuel used between "two up and light on" and a "full vehicle around the GVM" when we gas up at Carnarvon at the end of the day is about 10 to 15 litres

So extra weight equals extra fuel generally speaking ... will that do? Usually the metric I use!!! LOL Weight also equals greater revs to create greater power for potentially a greater time when stop/starting also, and that goes a long way towards affecting consumption also. Great posts from all though .... Good topic!

[MQ MAD]

Whats economy IF ya need the power for pulling the wieght ???
Compare a GU 2.8 Vs a GQ 4.2 pettie
I use these as i had a GU,now the GQ
Pulling loads up hills the TB does it with absolute ease,wheres as the same for the GU its a bit harder
You have to flog the smaller engine harder to do what the larger engine does
This then results in the smaller engine using more fuel
Then there is the aerodynamics to factor
But,is this that relevant
Comparison ,
A new camry returns 9-10l/100Ks economy,
Sleek late model car
But My old MQ 3 tonne brick returned the same economy

Excess wieght does effect economy some what
But next trip ya do just mention to the minister she must stay home,cause ya wanna save a few $$$ on fuel
I think sleepin on the couch wont be nice

[Bigrig]

Whats economy IF ya need the power for pulling the wieght ???
Compare a GU 2.8 Vs a GQ 4.2 pettie
I use these as i had a GU,now the GQ
Pulling loads up hills the TB does it with absolute ease,wheres as the same for the GU its a bit harder
You have to flog the smaller engine harder to do what the larger engine does
This then results in the smaller engine using more fuel
Then there is the aerodynamics to factor
But,is this that relevant
Comparison ,
A new camry returns 9-10l/100Ks economy,
Sleek late model car
But My old MQ 3 tonne brick returned the same economy

Excess wieght does effect economy some what
But next trip ya do just mention to the minister she must stay home,cause ya wanna save a few $$$ on fuel
I think sleepin on the couch wont be nice

LOL!! point taken .. and btw, she won't travel in Tank anyway - goes everywhere in the rubicon!!! So I'm on a winner there!!

Engine technology has a lot to do with it, as does aerodynamics, weight, gearing, tyre pressure, road type, etc ... the way I figure it, you buy what you know you can afford to run ... and in working that out, add 50% to what you think you are going to pay - reason? You'll probably do more off road which is nearly impossible to predict, and fuel prices aren't going to go down OR stay static over the life of the vehicle ... they'll only rise unfortunately!

[nowoolies]

hay mad
you come around and tell her who must be obeyed
im going down the pub,................ give me a call and let me know what emergency ward your in ill come a say g`day
rotflmao