Real-world fuel economy figures (daysul)

Yakuza

So, I was bored (and had time to kill) yesterday while driving down from Birmingham to Portsmouth (catching a ferry to Spain), so I decided to measure my car's performance at various speeds on the open road.  I used cruise control, measured the speeds using the gps (speedo was overstating by about 6%). The route was fairly level, and on motorways / A-roads (M40 and A34) and I was in 6th gear the entire time.

The car is a Qashqai+2, 1.5 dci. I had brimmed her in Dublin (including having shoved in 500ml of STP gunk cleaner before getting on the Holyhead ferry), just me and my luggage in the car. I reset the calculator between each phase and let the figure settle down before noting it. Here's what I got:
  90km/h - 4.6 l/100km
 100km/h - 5.1 l/100km
 110km/h - 5.6 l/100km
 120km/h - 6.4 l/100km (a tad over the limit, oops:D)

It would appear the sweet spot is around 110 km/h for me, before the extra speed starts to eat into the economy. Has anyone else done anything similar, or am I just a saddo?

I've driven 1000s of km in rented 2-litre BMW diesels, and they get 5.6 l/100km at 120km/h

Any more real-world fuel economy figures for long journeys out there? I am mildly curious as to where my mundane mode of transport fits on the scale of things. The truth be told, I'd rather have taken my previous car (E46 320i) for a blast down the motorways as (to steal a phrase used elsewhere in this forum) I'd have gotten many more smiles per gallon with it

pajo1981

I've done something similar.

Just be aware that even a slight incline can skew the figures quite a bit.

For total accuracy you'll need to drive back the way you came and get the average of the two rates.

Nerdlicious stuff, though - keep it up. And for gods sake don't attempt any of this in a car not fitted with rain sensing wipers.

650Ginge

I am currently doing some test runs along the m2, nothing illegal just 80, 90, 100, 110, 120, in both directions, multiple times to allow for an average taking different wind conditions into account in my Prius.

Will post up the results when I am done.

Surely get 4.6 at 90 is 22% better than 5.6 at 110. So u will get 732 kms instead of 600kms, 132 free kms that sweet, but u might go mad.

TheBazman

Life's too short :-)

650Ginge

650Ginge wrote: »

I am currently doing some test runs along the m2, nothing illegal just 80, 90, 100, 110, 120, ..............
Surely get 4.6 at 90 is 22% better than 5.6 at 110. So u will get 732 kms instead of 600kms, 132 free kms that sweet, but u might go mad.

speeds of 80 and 90 on the M2?

JJJJNR

I've been doing the same this last week and been getting great results, I'm over driving everywhere at 180 km/h and am taking a more sedate approach these days.... Actually im really impressed with the return my 2.0Tdi is giving.. no science but I've limited my speed (within safety) to maximum 110 km/h.

Can someone help with the maths? I brimmed my car with 53.63 L on monday morning, tank is 55L and I've covered 370km so far this week, I presume i need to brim again today to find out how much fuel I've used.

voxpop

Fuelly.com is handy for tracking this stuff.


You need to brim, run till very near empty - take note of mileage, then rinse and repeat a number of times to get an average.

Zubeneschamali

650Ginge wrote: »

Surely get 4.6 at 90 is 22% better than 5.6 at 110. So u will get 732 kms instead of 600kms, 132 free kms that sweet

Say you do 1000 km, that's 46 litres of fuel instead of 56, save 10, that's €14 saved. At 90, it takes 11 hours 7 minutes. At 110, it takes 9 hours 5 minutes.

So you're saving €14 for an extra 2 hours on the road. Would you take a part-time job driving on the motorway for €7 an hour?

INEEDANID

BMW E39 520 2.2 PETROL M-SPORT

Worked the fuel consumption to be about 2.93 gallons per 110 miles on journey from Shannon to Kilkenny done about twice a week. That works out at about 37MPG. Doing the speed limit and passing out a few cars with the foot down.

Usual fuel consumption works out about 31-34 MPG on shorter journeys such as my everyday Sixmilebridge to Shannon journey of 12KM

Yakuza

Zubeneschamali wrote: »

Say you do 1000 km, that's 46 litres of fuel instead of 56, save 10, that's €14 saved. At 90, it takes 11 hours 7 minutes. At 110, it takes 9 hours 5 minutes.

So you're saving €14 for an extra 2 hours on the road. Would you take a part-time job driving on the motorway for €7 an hour?

That's a great, practical, analysis of why I wouldn't be arsed to drive at 90 on a long-term basis

Indeed, I meant to further elaborate last night ( but was a little flaked after two days' travelling) ; dividing the consumption by the speed yielded a figure around 0.051 for the first three readings, changing to 0.053 for the fourth. This indicated a roughly linear relationship between consumption and speed until 120km/h, where air resistance starts to kick in more, so 110 appears to be the optimum speed with respect to time spent travelling - in my car, at least.

Yakuza

Just an addendum; I drove from Portsmouth to Holyhead yesterday (M275/M27/M3/A34/M40/M42/M6/M56/A55) with two pitss stops along the way.

I drove mostly in the left hand lane at 100 (had 12 hours to drive 550 km; plenty of time) on the speedo (94 actual), with the odd sprint to overtake some slow-moving lorry before moving back into the left.

I got 4.8 l/100km until after our second stop, somwhere north of Birmingham (Keale services), when it started to go up to 4.9 and then settled on 5.0 from about the M56 onwards. I don't recall any steep gradients (and the overall trip was from sea level to sea level, more or less cancelling out the gradients) so I guess it was the AC working a little harder as the evening wore on and it was getting colder which upped the consumption.

I was quite surprised with the 4.8 reading (1 extra adult + 3 extra kids and all the luggage) that I got for the first 2/3 of the journey as I thought the extra weight would have badly affected the performance compared to that I had when travelling at that speed on the way down.

Overall, I was pleased to get 5.0 l/100km (approx 56 MPG in old money) over 550km in a heavily-laden car.

heate

BMW 7 series Zurich to Berlin.

At 120km/h flat enough slight incline through the mountains - 6.5l/100km

Very little traffic at 200km/h 11l/100km cruise set at 201

Not bad for a v8

MugMugs

RoverJames wrote: »

650Ginge wrote: »

I am currently doing some test runs along the m2, nothing illegal just 80, 90, 100, 110, 120, ..............
Surely get 4.6 at 90 is 22% better than 5.6 at 110. So u will get 732 kms instead of 600kms, 132 free kms that sweet, but u might go mad.

speeds of 80 and 90 on the M2?

So that was you making me late this morning?

vectra

On the motorway Cork to Dublin tody heading to Edenderry to view a Bucket :P

held it around 130/135
Screen was showing 5.6/100

EPM

Just pulled in for a smoke near cashel doing Carlow to Cork at 120. Currently showing 5.4...I'll update later sure compared to the usual.

650Ginge

Zubeneschamali wrote: »

Say you do 1000 km, that's 46 litres of fuel instead of 56, save 10, that's €14 saved. At 90, it takes 11 hours 7 minutes. At 110, it takes 9 hours 5 minutes.

So you're saving €14 for an extra 2 hours on the road. Would you take a part-time job driving on the motorway for €7 an hour?

That one way of looking at it, put you are spending money that you already got paid, for doing what ever you do and at what ever rate you get for doing it. So it is a finite resource, we choose how we spend it. If you can save €14 a tank then you dont have to go out and take a job driving at €7 an hour. It is not huge money but it is after tax money. So if you can save €14 a week then that is €728 before tax and closer to a €1400 pay raise for most of us. €728 is a nice holiday, or the road tax on a 928. You choose how to spend it, be it in petrol going a bit faster or a holiday or whatever. The difference increases the bigger the difference in speed, the savings could be a lot more.

By the way where do I get 10 ltrs of petrol for €14.

unkel

650Ginge wrote: »

€728 is a nice holiday, or the road tax on a 928.

If only! Sadly the motor tax on a non-vintage 928 is €1,566

650Ginge

Well I actually meant the €1400. I would dearly like a 928, but I have to sell something first and nothing is shifting.