Most efficient speed for xc90 2005 D5?

[adrian198]

Hey all.

I have a kind of random question. What is the best speed to drive at for best fuel consumption? My guess would be 90kmh? But how much difference does 120/130kmh do?

I am going on a 5000km (3000 mi) road trip with my 3 friends and was just wondering what is the best speed to travel at when going on the autobahn.

Thanks, Adrian

[Tannaton]

Originally Posted by adrian198

Hey all.

I have a kind of random question. What is the best speed to drive at for best fuel consumption? My guess would be 90kmh? But how much difference does 120/130kmh do?

I am going on a 5000km (3000 mi) road trip with my 3 friends and was just wondering what is the best speed to travel at when going on the autobahn.

Thanks, Adrian

Hi There,

You don't say whether you have the 163 BHP E3 car with the 5 speed box or the 185 E4 car with the 6-speed box (or a manual ?)

I would say 56 mph - this is the point at which the torque converter locks in top gear and the drivetrain is most efficient. Any speed below this, you have losses in the transmission and torque converter, every 1mph above that you increase the inevitable aerodynamic/wind resistance losses. So that is 90 kmph as you suggested.

If it's the 6-speed the TC lockup point may be at a lower speed depending on the software version.

Driving at 120 kmph (75 mph) you will use at least 25% more fuel I guess.

[Dastardly Diesel]

56 MPH. That's the speed at which the extra urban consumption testing was done and all manufacturers tweaked maps, gearing etc to be as economical as possible at the tested speed.

[Bashy]

Originally Posted by Dastardly Diesel

56 MPH. That's the speed at which the extra urban consumption testing was done and all manufacturers tweaked maps, gearing etc to be as economical as possible at the tested speed.

Interesting, I have the 6p auto 185bhp, i use cruise control a lot, as often as i can because it actually shows as more economical. I have been in 30 limits in 4 or 5th gear with cc on and seen instantaneous hover around 60-70mpg, you cant get that at 56mph...

Unless of course, they mean a speed thats of any use, eg, you wouldnt really use 30 in a 60 limit so prob referring to a cruising speed when they came up with 56?

[Dastardly Diesel]

Instantaneous is one thing. Achieving a high average is another. At 70 I can get 'infinite' MPG by lifting off or driving down a hill, but that won't make much of an average.

[Tannaton]

I have an old car mag from 1990 which has a advert for the Rover Montego Diesel which did 102 MPG when they drove it round the Milbrook bowl at 30 mph... not a realistic option for commuting though.

The key point here on the XC90 (with auto) is to get to speed where the torque converter locks up so there are no losses to heating the hydraulic fluid. On the early cars with 5 speed boxes this is 55 mph in 5th, 40 mph in 4th if you select 4th with geartronic. On 6-speed boxes it depends on the year, some lock up at much lower speeds.

[Moose Test]

Originally Posted by Tannaton

I have an old car mag from 1990 which has a advert for the Rover Montego Diesel

I don't suppose I could have a quick look at it round the back of the bikesheds?

My father owned one in the mid-eighties and I remember thinking it was futuristic! And that's before we consider the synthesised voice of the MG model.

What a shame BL made them all out of rust and sealing wax.

[S60D5-185]

Originally Posted by Tannaton

On 6-speed boxes it depends on the year, some lock up at much lower speeds.

Any more info on this Tannaton?

Just curious as to what speed lock up is on my 2007.


Thanks.

[ianu]

Hi Adrian,
It's a great car for a road trip - no need to worry about luggage space with just 4 of you.
It would help if you could say if it's a auto or manual and 163 or 185bhp although reality in mpg terms may only be +/- 5. 2005 model I would hazard an auto as manuals weren't as popular then. 163 or 185 - lift the bonnet - if the plastic engine cover is black it's 163 iirc, 185's were grey I believe.
Optimum speed I found on several trips across France / Austria really does depend on load and road.
I've got a 163 manual (2004 - 05 Model year), and you kind of get a sense of when the momentum of the car with the weight you're carrying is just pushing the car along with little effort on the throttle. Mine at times seemed very happy to roll along at anything between 100kmh and 120kmh (65-75mph) with very little input from me. Over 75mph and you know your fighting the laws of physics.
Real world consumption was between 10km/p/l - 13.5km/p/l (30 - 38mpg).
Some of these trips were 6 or 7 up with a roof box - again I think the weight once it's moving you sense where the optimum speed is.
Have a great trip :-)

[adrian198]

Sorry! Should have been more specific.

The car is a 2005 D5 163hp with the 5speed trans!

So 55 mph is the most efficient. Gotcha!!