Fuel Economy - Highway driving

GoonPillowGoonPillow Junior Member
edited February 2017 in Fuel and Oil
Hey everyone,

About to embark on a big trip from Darwin to Canberra soon. Has anyone found that sweet spot you should cruise at down the highway where you won't be chewing a shitload of fuel and basically sitting on boost the entire time?

I haven't had the chance to test it out which is why im asking. NT has from 130km/h - Open speed limits. Should i be sticking to 120... or less? or can the rok sit comfortably on 130-140? or will it be perm on boost at those speeds?
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Comments

  • VolkarokVolkarok Banned
    edited March 2015
    GoonPillow wrote: »
    Hey everyone,

    About to embark on a big trip from Darwin to Canberra soon. Has anyone found that sweet spot you should cruise at down the highway where you won't be chewing a shitload of fuel and basically sitting on boost the entire time?

    I haven't had the chance to test it out which is why im asking. NT has from 130km/h - Open speed limits. Should i be sticking to 120... or less? or can the rok sit comfortably on 130-140? or will it be perm on boost at those speeds?
    What are your aerodynamics like?
  • rokbottomrokbottom Senior Member
    edited March 2015
    You will be sitting on about 6psi even at 100 kp/h from memory.

    I find around 90-100 is best, but not real practical :(
  • GoonPillowGoonPillow Junior Member
    edited March 2015
    running a arb deluxe bullbar, apart from that its stock
  • Walrus48Walrus48 Supporting Member
    edited March 2015
    At 110 with AT,'s full Long Range Tank, awning, two up and possibly 250kg of gear mid to high 9's. Drop to 100 and that gets down to mid to high 8's depending on headwind and hills.
  • HadesHades Supporting Member
    edited March 2015
    Driving between Katherine and Darwin I usually get around 10.8-11.2l/100km. That's sitting on 140 on the speedo.
  • TBRokTBRok Forum Slave
    edited March 2015
    [MENTION=5305]GoonPillow[/MENTION] I recently did a trip out to Ayers Rock and sat at 130k/hr all the way, even through the open speed zones. I averaged about 13.5L/100km. At 110k/hr that dropped to about 11L/100km. I'm on 285s, canopy and was fully laden with a couple of things on the roof. Take plenty of spare fuel (maybe 40L), plan your fuel stops and you'll be right.
  • VolkarokVolkarok Banned
    edited March 2015
    GoonPillow wrote: »
    running a arb deluxe bullbar, apart from that its stock
    Stock as in open tub? If so thats a killer.
  • BerKoBerKo Senior Member
    edited March 2015
    Volkarok wrote: »
    Stock as in open tub? If so thats a killer.

    Lol myth busted:http://m.youtube.com/watch?v=r3aqHbD-O9E . seems like you need a mesh tailgate.
  • Mark PeaceyMark Peacey Member
    edited March 2015
    Walrus48 wrote: »
    At 110 with AT,'s full Long Range Tank, awning, two up and possibly 250kg of gear mid to high 9's. Drop to 100 and that gets down to mid to high 8's depending on headwind and hills.

    I can only dream of such economy. The best I ever get is about 10.5 at those speeds. I have had a stage 1 tune. I have a tray plus a TJM bullbar with no winch.
  • VolkarokVolkarok Banned
    edited March 2015
    BerKo wrote: »
    Lol myth busted:http://m.youtube.com/watch?v=r3aqHbD-O9E . seems like you need a mesh tailgate.
    Open tub is much worse than a canopy or a hardlid or a hardlid with ttt (tub top tent).
  • Walrus48Walrus48 Supporting Member
    edited March 2015
    Right foot (go and stop) issues are much worse than open tub or canopy or hard lid, I would think it would depends on the number you apply to "much worse" .02, .05, 0.7, 1.0....... Litres /100km also. Not much use trying to micrometer a watermelon, that just leads to analysis paralysis.
  • VolkarokVolkarok Banned
    edited March 2015
    Walrus48 wrote: »
    Right foot (go and stop) issues are much worse than open tub or canopy or hard lid, I would think it would depends on the number you apply to "much worse" .02, .05, 0.7, 1.0....... Litres /100km also. Not much use trying to micrometer a watermelon, that just leads to analysis paralysis.
    I suggest you read or reread the first post in the thread.

    The difference between an aerodynamic vs unaerodynamic rok above 110km/h would be 2 or 3 or 4L/100km, the higher the speed the more the difference would be.
  • ozcaddyozcaddy Supporting Member
    edited March 2015
    First post does not say whether it is a diesel auto or manual or petrol auto or manual , so I think there could be 4 sweet spots
    I think we should go for a bit of clarity [MENTION=5305]GoonPillow[/MENTION]
    Whats that old saying the devil is in the detail
    Oz
  • Walrus48Walrus48 Supporting Member
    edited March 2015
    Volkarok wrote: »
    I suggest you read or reread the first post in the thread.

    The difference between an aerodynamic vs unaerodynamic rok above 110km/h would be 2 or 3 or 4L/100km, the higher the speed the more the difference would be.


    Took your Sage advice (or snide remark) and read then reread post #1......Tick

    Fully concur regarding aerodynamic vs not aerodynamic above 110km/hr could be 2, 3, 4 or more L/100km and agree the higher the speed the greater the difference could be.....Tick

    #6 and #7 give input regarding speeds above 110kph I was offering my input as data to go with other responses and highlighting some of the variables that may need to be considered. One of my weaknesses is that I don't know everything.
    [MENTION=1381]ozcaddy[/MENTION] yes it is! and you still shouldn't try to micrometer a watermelon
  • HadesHades Supporting Member
    edited March 2015
    Volkarok wrote: »
    Open tub is much worse than a canopy or a hardlid or a hardlid with ttt (tub top tent).

    Having driven to and from Darwin multiple times with the canopy and without (open tub and with and without sports bar) the difference is negligible. The difference might be all of .2 of a litre per 100 km at 130kmh. So if you were to empty a whole tank, 80L, there is 1.6l in it, or 2%. So it is in fact not as you say, "much worse".
  • HadesHades Supporting Member
    edited March 2015
    The canopy on, is worse than the open tub at that speed.
  • WallyspikeWallyspike Supporting Member
    edited March 2015
    Fuel economy is generally at its best (the 'sweet spot') at about the speed you hit top gear. That is, about 80 - 85Kph. How much used will depend on the aerodynamics of the car. For example, mine has a bull bar, canopy and AT tyres, all of which will bugger up the economy even at 80. After that, it goes pear shaped. Many reports have been done, but overall, fuel usage goes up exponentially with speed. At full loud, a Vayron uses 78 L/100K, but that is at 407 KPH! This compares to 17 L/100K at 'normal' highway speeds.

    I have seen reports of airlines slowing down marginally to save fuel and have also done some work with pilot boats where a 2 knot reduction made major savings, so it seems to hold true wherever there is drag.

    If you want economy on the highway, don't get a Rok or any other fourbie. (Nor a Prius - good in town but...) If you are concerned with economy, keep the vehicle smooth on the outside and don't carry extra crap. But if you're like me, who cares?
  • Tornado_ALIVETornado_ALIVE Forum Addict
    edited March 2015
    Volkarok wrote: »
    Open tub is much worse than a canopy or a hardlid or a hardlid with ttt (tub top tent).

    Mmmmmm........ No. Do yourself a favour and watch that video.
  • Tornado_ALIVETornado_ALIVE Forum Addict
    edited March 2015
    I average about 10s @ 100 Kmh however I am running 265/75/R16 ATs, canopy, awning roof tray and a heap of weight on board. High 10s @ 110kmh. If I drop down to 80, I can get 8s. I find my most efficient is 70kmh in 5th gear.

    Accurate averages are hard to get as even a slight headwind can make a difference.

    I now have an ECU tune so we will see how the economy goes...... It is crap at the moment as I have been testing its new top end performance :D
  • BerKoBerKo Senior Member
    edited March 2015
    Volkarok wrote: »
    I suggest you read or reread the first post in the thread.

    The difference between an aerodynamic vs unaerodynamic rok above 110km/h would be 2 or 3 or 4L/100km, the higher the speed the more the difference would be.

    I disagree completely.... look at the VW crafter and amarok with the same spec... The crafter is a friggin monster of a brick shaped van. Same 2ltr twin turbo 400nm engine. The difference is less than 1.5l/100km combined and even less on the open road (just over .5l/100km). IMHO you will change your fuel much more by altering ratios (tyres/driveline) than you ever will by changing aero.
  • ozcaddyozcaddy Supporting Member
    edited March 2015
    GoonPillow wrote: »
    Hey everyone,

    About to embark on a big trip from Darwin to Canberra soon. Has anyone found that sweet spot you should cruise at down the highway where you won't be chewing a shitload of fuel and basically sitting on boost the entire time?

    I haven't had the chance to test it out which is why im asking. NT has from 130km/h - Open speed limits. Should i be sticking to 120... or less? or can the rok sit comfortably on 130-140? or will it be perm on boost at those speeds?

    Can some-one point out to me exactly where in the above post it mentions the type of motor or gearbox as apparently i have been reliably informed it does contain said information , over to you [MENTION=1351]Walrus48[/MENTION] and fellow forum members
    I have never used a micrometer on a watermelon I go by taste (lol)
    Oz
  • VolkarokVolkarok Banned
    edited March 2015
    Hades wrote: »
    Having driven to and from Darwin multiple times with the canopy and without (open tub and with and without sports bar) the difference is negligible. The difference might be all of .2 of a litre per 100 km at 130kmh. So if you were to empty a whole tank, 80L, there is 1.6l in it, or 2%. So it is in fact not as you say, "much worse".
    When i first had my car and drove at 110km/h with empty tub i noticed the dte plummet and the engine made significant extra noise and there was buffetting.

    When i filled the tub similar to a hardlid (though not quite as good) and did a long trip at high speed those factors were not significant.

    When i drove back on that trip i had equivalent to a hardlid with tub top tent above it, and things were even better again, to my great satisfaction.

    When volvo ran their wagon in the touring car series rather than their sedan its because the wagon had better aerodynamics. The general theme in aerodynamics has been that wagons have better aero than sedans.

    I think its pretty obvious that an open tub has horrendous aero. Sure wind patterns and spirals can moderate things but its still a long way from aerodynamic.
  • VolkarokVolkarok Banned
    edited March 2015
    BerKo wrote: »
    I disagree completely.... look at the VW crafter and amarok with the same spec... The crafter is a friggin monster of a brick shaped van. Same 2ltr twin turbo 400nm engine. The difference is less than 1.5l/100km combined and even less on the open road (just over .5l/100km). IMHO you will change your fuel much more by altering ratios (tyres/driveline) than you ever will by changing aero.
    I have visited forums about aero and mythbusters have done shows about it and heaps of other background info. Aero makes a big difference at high speeds.

    Vans arent as bad as you might think because the consistent one box shape reduces turbulence. The shape of the back is significant though. An egg with the blunt end facing forward is a very aerodynamic shape, and a torpedo is a sleeker variation of the theme.

    I read an article about a van driven at high speed and when they folded the wing mirrors back it added 5 to 10km/h to the top speed of it.

    People have reported on numerous forums that adding a rtt cost them say 1.5 to 2L/100km, at say 100km/hr.
  • VolkarokVolkarok Banned
    edited March 2015
    Mmmmmm........ No. Do yourself a favour and watch that video.
    I had already seen it, but i mostly knew the answer already before that. The eckman(?) spirals help but still dont make it aerodynamically efficient.
  • rokbottomrokbottom Senior Member
    edited March 2015
    What shape is the cross section an aircraft wing and why?
    Laminar flow.
    Turbulence and low pressure at the rear of any vehicle will increase its drag coefficient.
    Then again I may be wrong.
  • Walrus48Walrus48 Supporting Member
    edited April 2015
    Volkarok wrote: »
    The eckman(?) spirals help but still dont make it aerodynamically efficient.

    Possibly you are referring to drag vortices? I think the eckman principle refers to wind blowing across sea currents making them turn left or right.
  • VolkarokVolkarok Banned
    edited April 2015
    rokbottom wrote: »
    What shape is the cross section an aircraft wing and why?
    Laminar flow.
    Turbulence and low pressure at the rear of any vehicle will increase its drag coefficient.
    Then again I may be wrong.
    Aircraft wings are designed to create low pressure on the top of the wing to generate lift.

    The transition from the middle 'box' to the rear 'box' on a sedan or hardtop creates turbulence that a wagon doesnt create. At the end of the day the projected area of the cabin will be replaced by air as it moves past and the wagon just does it more neatly.
  • VolkarokVolkarok Banned
    edited April 2015
    Walrus48 wrote: »
    Possibly you are referring to drag vortices? I think the eckman principle refers to wind blowing across sea currents making them turn left or right.
    I think i got the term from air moving over fences and trees and turning over itself like a breaking wave, but i am figuring its a basic principle which may have more than one name.
  • ozcaddyozcaddy Supporting Member
    edited April 2015
    Does anybody know what type of motor and gearbox [MENTION=5305]GoonPillow[/MENTION] has got in his Amarok , reading the last couple of posts I think it might be a Merlin or Napier
    Oz
  • HadesHades Supporting Member
    edited April 2015
    I have seen kit aircraft with a Subaru Boxer in them... maybe it's one of those.
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