most fuel efficent speed

[4dlvr]

any one know for a fact what the most fuel efficent speed is on a 6cyl au???
i was at 70 a i was doing 13l/100km then at 90 it was reading 11l/100km, and then i driving constently at 140 and it was reading 7l/100km.
it seems the faster i go the better fuel econamy i get.
so a tip to save fuel???? drive fast

[DoreSlamR]

i'd say 90-100 kays would be the most economical, doing 140 you'd be getting pretty close to 3000rpm so i dont see how that could be more economical. shame i doesnt work that way ;)

[JC]

0. With engine off for best economy, or even with engine on, it will idle for hours and hours on a full tank.

Seriously, you use 10% more fuel doing 130 compared to 110. I would say your instant fuel consumption display is just having a best guess.

[Mechan1k]

I find in some instances 90 is better than 100-110.
But it depends on the road (incline, country road, freeway, highway) and the mood I am in at the time.

Long distance freeway was the best I did find while not going over 110km/h ... 120 was using more I found.

[HLC]

i think 80 in top gear (4th/5th depending on Auto/Man) worked out to be the most economical speed.

[The Monty]

105 with aircon on. I get a hundred extra k's from the tank when I have air con on. That is no bull either, its weird but true.

[blackers10]

id definatly say 90-100kmh on cruise control
with aircon OFF .. sucks SO much power for the uphill runs..

[Mr_4.0]

80km's in top gear is the best. nearly EVERY car gets its best economy at 80km/h.

this is only in factory form though.

[T3man]

For an AU there isn't much difference in fuel consumption between 80 and 110km/h. Anywhere in this range and you'll be doing OK. This is because the CD of the AU is very low - less than 0.3. For most older cars 80km/h is the most economical speed. This is because wind resistance increases markedly once you get above 80.

[StealthAu]

get an economy gauge, that will tell you ideal speed for minimum fuel consumption

[kryzak260]

145KPH. When i drove my VCT Fairlane over to Perth in 04, we got 100KMs more per tank with cruise on 145 that we did with cruise on 130. Could have something to do with the VCT though.

The engine is somewhere between 3000-3300 RPM which is good for economy because it is close to peak torque. Apparently an engine is at it's most efficient at peak torque because it doesnt have to work as hard to keep moving.

[jonbays]

The dash readout isn't really that accurate.

As most seem to agree 80-90kmh will be the best speed for economy.
After that the wind resistance load increases by the cube and falcons are not small even though the drag coefficient is pretty good. The old 185kw XR8 could do 245kmh out of the box.

[Dauphin]

When I drove on a trip to Albury last year, I watched my economy very closely. Most experts tell you that doing 90 km/h instead of 100 km/h on the freeway is better for fuel economy. I found it didn't make any improvement, going on my Ghia trip computer. But if the revs are lower in the same gear, then surely that means something.

My car has a hi-stall torque convertor so it may be a little different.

My transmission lockup occurs at 90 km/h so I try to stay there and above if I can, if the speed limit allows. At 80 km/h my car does 2,000 revs. Once it gets to 90, it locks up and does 1,900 revs. 100 km/h is 2,000 revs.

They are only little variances but over a period of time I imagine it all adds up on a trip.

I noticed something interesting the other night. Climbing up the West Gate Bridge doing 60 for road works, my car was doing well above 2,000 revs. I slipped it down to 3rd and the revs decreased by several hundred. I guess it was "straining."

Hope that helps.

[superroo]

I've found according to the dte (which i reckon i a good estime of economy, not distance) is that sitting dead on a 100 is best. personlly there is a difference between 100 and 110. This is with a manual though.

Cheers

[loop]

I seem to recall that Ford recently did a test for fuel efficiency, and said that they set their cruise control for 90km/h.

[Cooper69S]

I assume most cars achieve their peak efficiency at around the same speed (80-90) because they all have to follow the same cycle when they set the australian standard fuel consumption, so they are probably designed around that point to some extent...

I was driving 120km each way to work and back for a few months. moved work sites now so "only" doing 80km each way. anyway point is that gave me plenty of opportunity to test the efficiency of different speeds. with the v8 (before i went dedicated gas) i was getting around 730km a tank if i kept below 100kmh. that dropped to 680 if i went 105-110, and 630-650 if i sat on 110 or slightly over. i didn't try any full tanks at 90kmh because i like to get to work on the same day that i leave home... but going by brief stints at that speed, according to the DTE it wasn't that much better than 100. Anyway i worked out doing 100 or just below saved me about $5 a day compared to 110-115kmh.
now with the gas and shorter distances it doesn't matter so much so i just do 110. sitting on 95-100 gets boring...

[AUIII XR8 MAN]

I found in my XR8 that sitting on 115km/h on the freeway is the sweet spot for my car. I found that driving any slower it was use the same amount of fuel, any faster it uses more. Yet the Lazer 100km/h is the sweet spot for it. It's finding the right rev at any speed so you are lightly on & off the accelerator well give you the best fuel economy for any car.

[Eu-GenixX]

those trip meters can be a bit misleading...

coz it takes into account the cars speed.. not just the distance travelled vs fuel comsumption...

which is why if you let it idle and creep you get like 99l/100km.. hence why the faster you go.. it appears you are getting better fuel consumption.. it's just coz you are travelling the distance quicker...

by most accounts i hear 90km/h is the best for fuel..