MPG at varying speeds

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bluestreak56

Veteran
 Maidenhead
Driving down the M1 today, I tried varying my speed in my 3l coupe.

I found that sitting around 60mph got my as high as 47mpg and an average of around 45mpg.

While sitting at 70 mph got me to around 38-40mpg.

When I got a little bit "right foot heavy" and sport mode on, I managed to drag it down to 35mpg but never less than that.

I found this quite a difference between the speeds, can anyone else confirm this is the same for them?
 
I take it it's a 3.0si?

Managed 36mpg average on a long 200 mile motorway journey at 78mph - which fits into your figures.

:driving: :thumbsup:
 
Aye...

I averaged 41mpg from Edinburgh to Derbyshire in my 3.0si...

Could have easily got more but was sitting between 70-75mph most of the way..
 
I had to drive my Z to london for work on wednesday (long story) but as i was claiming milage i was uber frugal... Stuck to 65-70 even down the m6 toll (was the slowest car there)

Filled up the tank before and after and £37 got me 305 miles!! Thats better then my 120d at normal motorway speeds!


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Constant speeds will generate good MPG if you're cruising in 6th.

I haven't managed to break 30mpg so far in my new zed


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bluestreak56 said:
I found this quite a difference between the speeds, can anyone else confirm this is the same for them?
Click to expand...
The reduction in mpg as speed increases when in the same gear is all down to aerodynamic drag which increases in accordance with the velocity "squared". This relationship is exponential and not linear: aerodynamic drag is 4 times greater at 80mph than it is at 40mph. In other words, the faster you travel the greater the rate of fuel consumption.
 
Just found this:

The Energy Saving Trust says that the most efficient speed you can travel in a car in terms of achieving the best fuel economy is 55-65mph. Any faster, though, and the fuel efficiency decreases rapidly. For example, driving at 85mph uses 40% more fuel than at 70mph (oh, and it's illegal too).

from here:

http://www.theguardian.com/environment/green-living-blog/2011/mar/25/hypermiling-tips
 
I just went on a 140 mile motorway journey 70 mph all the way 50 in x2 sets of road works. 40.9 MPG...3.0 Si roadster. Pretty good stuff.
 
3.0Si Coupe - I must be doing something wrong - I have yet to break 30mpg on average with a mix of motorway and commuting! Barely get 300 miles out of a tank. Mind you I don't sit on the motorway at 65-70 mph either, but still! I'd be happy with anything above 30mpg never mind 40mpg!
 
I achieve 24 mpg averaging 26 mph in my 2.5Si :lol:

Reading people on here getting better on a m is a bit distressing. I only do 4k annually so not been urgent to investigate but about time. I have had all physical checks done but not software.
 
gordongecko500 said:
3.0Si Coupe - I must be doing something wrong - I have yet to break 30mpg on average with a mix of motorway and commuting! Barely get 300 miles out of a tank. Mind you I don't sit on the motorway at 65-70 mph either, but still! I'd be happy with anything above 30mpg never mind 40mpg!
Click to expand...

No you're not doing it wrong, the people claiming to be getting 40mpg+ are the ones doing it wrong. I hazard a guess what they mean is that they reset the MPG when the engine has warmed up and while they are cruising at 60mph. That's cheating, for it to be a real 'average' reading it needs to include the town/stop-start driving and cold start too.

That's why my reading on any long journey is never more than 32mpg - it takes me 30 minutes to get out of London, by which time it's as low as 20mpg. It's then impossible to make that loss back up again. But at least it's an accurate reading.

Sorry but a 3.0 petrol will not 'average' 40mpg on any journey, that is pure fantasy.
 
Ive averaged 27.1mpg in the last 4 months mostly long journeys tho, including all town driving. Haven't reset it since november.
 
Sorry but a 3.0 petrol will not 'average' 40mpg on any journey, that is pure fantasy.[/quote]

Ermm its not fantasy...I have checked the MPG read out and it is accurate to filling your car brim to brim and working out the figures.
I filled my car up 1.5 miles from home Zeroed everything and drove back to my house which is uphill through town...MPG reading 25 MPG not a good start.
I left stoke on trent 7am sat morning traffic pretty clear.
Got up to 70MPH on M6 then cruise control all the way at 70MPH.
Got off M40 into Thame (Oxon)
final read out 40.9 MPG from Stoke on Trent to Thame.
 
Are you sure youre not reading the av mph. By mistake
M

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Ooch said:
Ermm its not fantasy...I have checked the MPG read out and it is accurate to filling your car brim to brim and working out the figures.
I filled my car up 1.5 miles from home Zeroed everything and drove back to my house which is uphill through town...MPG reading 25 MPG not a good start.
I left stoke on trent 7am sat morning traffic pretty clear.
Got up to 70MPH on M6 then cruise control all the way at 70MPH.
Got off M40 into Thame (Oxon)
final read out 40.9 MPG from Stoke on Trent to Thame.
Click to expand...

OK, so you did a 125 mile journey, 1.5 miles of which was through town with clear traffic and the rest was on a clear motorway. Yes, if only 1% of your journey is not motorway cruising, you can probably do 40mpg on a trip. But is that an average journey? No, an average journey is probably at least 10-20% town driving, with a fair bit of stop-start motorway driving too, and that is what kills the average MPG.

As said I know these cars CAN do 40mpg, but there's a big difference between it being possible under ideal conditions and real-life MPG.
 
So in summary.....

Yes you realise they can do 40mpg plus or is it a pure fantasy?

I reset when i set off from Ediburgh....A720,A702,A721 and picked up A72 (M)....M6,M61,M60 to M67.....

Granted...a lot of Motorway but plenty of A roads too..... 40mpg is easily achievable on a run.
 
bluestreak56 said:
Just found this:

The Energy Saving Trust says that the most efficient speed you can travel in a car in terms of achieving the best fuel economy is 55-65mph. Any faster, though, and the fuel efficiency decreases rapidly. For example, driving at 85mph uses 40% more fuel than at 70mph (oh, and it's illegal too).

from here:

http://www.theguardian.com/environment/green-living-blog/2011/mar/25/hypermiling-tips
Click to expand...
So if I currently average 27mpg at a GPS-indicated 85mph, then I'll get 38mpg at 70mph?

I think they're talking bollocks :P
 
Keep it on the motorway don't go over 70 you can get 40 MPG from the 3.0 SI. That was 3 miles of town driving rest a good run on motorway with no stopping or hold ups. (127 miles)
Take all the other 3.0L petrol makes and models out there (not sure about very new models) and I would be suprised if any could match that.
 
I don't think I've managed 25mpg as yet! But then - I only really use the car on the weekends to have a bit of fun and enjoy driving!
 
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