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Bishop

Full Member
Jan 25, 2014
1,540
476
Inside the wire, Llanelli
Vaguely recall something about 'urban mpg' tests being based around an average of 50 mph, so modern vehicle designs are tweaked to be more aerodynamically slippery at that low speed range giving more economical/greener performance figures. With traffic congestion getting worse every year we may be the last generation to travel the roads at such heady speeds as 70mph.
 
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Broch

Full Member
Jan 18, 2009
3,766
2,932
Mid Wales
You should run the experiment Broch ... hop in the car and see what yr fuel gauge says after a there and back. I have read that driving at 85mph uses 40% more fuel than at 70mph ... there was a lot of reporting on this in 2014
You may be right actually. Just doing a crude calculation of wind pressure between 50 and 70mph would suggest a doubling of wind resistance - maybe they're right after all :)
 
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Janne

Guest
Feb 10, 2016
12,368
2,262
Grand Cayman, Norway, Sweden
Huge number of variables. The states like to make us believe that lowering the speed is the answer, but it is not.
For safety - yes.
Not for me though. I love high speeds, and driving on excellent roads at a ridiculously low speed makes me grumpy, angry and unpredictable.
:)

You might discover that your own car engine runs much more efficiently at the revs needed to run it at 70 mph in top gear than at 50 mph in one gear lower.

There is one more negative effect. If the speed is lowered substantially, the road will not 'empty' as quickly, and tailbacks can happen.
 

santaman2000

M.A.B (Mad About Bushcraft)
Jan 15, 2011
16,708
988
63
Florida
Huge number of variables. The states like to make us believe that lowering the speed is the answer, but it is not.
For safety - yes........
Not really for safety either. During the period when our speed limit was 55mph the accident rate didn’t change.
 

Janne

Guest
Feb 10, 2016
12,368
2,262
Grand Cayman, Norway, Sweden
That is interesting. Maybe more people than me get stressed by driving slow on nice roads?
:)

Here, our max speed on just a few kilometres is 50 mph. The rest 40, 35 or 25 mph.

Yet we have many accidents and deaths considering the small population.
 

Broch

Full Member
Jan 18, 2009
3,766
2,932
Mid Wales
Not for me though. I love high speeds, and driving on excellent roads at a ridiculously low speed makes me grumpy, angry and unpredictable.
:)
I am lucky. I live in an area where the roads are fun within the speed limit. You can't beat drifting around winding mountain roads in a rear-wheel-drive sports car :)
 

Fadcode

Full Member
Feb 13, 2016
2,349
562
Cornwall
There are many factors other than speed which will make a car efficient, when I go to work a distance of about 12 miles I achieve 45 mpg going there and 58 mpg coming back, solely down to the fact I go up a long hill going, and cruise down the same hill coming back., now if I cruised down the hill coming back at about 20 mph, I can actually achieve something in the region of 110 mpg, this is because the computer calculates the mpg on distance and time.
Saying that I do not always believe what the computer says..................................very few cars can normally achieve the manufacturers stated mpg figures, as there are too many variables, roads, wind speed, temp, landscape, etc, etc,
 

Janne

Guest
Feb 10, 2016
12,368
2,262
Grand Cayman, Norway, Sweden
For best efficiency ( but dangerous so never, ever recommended!) you should put the car in Neutral and roll downhill. The higher exit speed - the longer your car will roll and only consuming ‘engine idling’ amount of fuel.

For me, driving a decent car is a pleasure. Cost of fuel is a minor problem.
 

GuestD

Full Member
Feb 10, 2019
1,445
685
Both SAAB and Rover (amongst others) offered cars with "freewheel" gear boxes.
http://www.bmh-ltd.com/wheelnut/wheelnut_1.asp

Citroen had the TraffiClutch, which was centrifugal/freewheel, and Trabant also had a freewheeling box.

And anyone familiar with Massey Ferguson multi power gearboxes will know that in low multi power there is no engine braking so it effectively is a freewheel.
 
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santaman2000

M.A.B (Mad About Bushcraft)
Jan 15, 2011
16,708
988
63
Florida
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Janne

Guest
Feb 10, 2016
12,368
2,262
Grand Cayman, Norway, Sweden
Absolutely.
If you do not burn some carbohydrates, somebody else will.
I am offsetting what I burn in cars, boat and airplane by being as environmentally friendly as I can.
Buying Local, recycling, not buying shortlived Far Eastern goods, stuff like that.
Buying cars that I keep forever. In fact, what we have now will stay with me until my Earthly departure.
 

Paul_B

Bushcrafter (boy, I've got a lot to say!)
Jul 14, 2008
4,651
697
Lancashire
My old fiesta had a speed if 56mph written in the manual as being the most efficient cruising speed. By the time I sold it that speed was impossible to maintain on some motorway hills even with a good run at them. I guess a few horses escaped the bonnet leaving only the old nags!
 
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