60 MPH Limit on Motorways

[biggbn]

Originally Posted by Laird Scooby

Yes if that move means we are not using tose resources to the maximum efficiency and given most cars designed over the past 30 years or so were designed to be most efficient at motorway speeds, i don't see that it will extend the time of using a finite resource.

Name me a car that gets better mpg at 70 or 80 than 60? Anecdotal evidence of the over 200 i have owned and countless I have begged, borrowed or stolen suggests...none. You may have evidence that suggests otherwise and thus contradicts every roadtest and manufacturers figure, or owners review I have ever read or heard about?

Edit, sorry Dave that sounds quite confrontational. Didn't mean it that way, just curious what you mean? Even my frugal wee mini will get over 70mpg at 60 and high 50s at 80?

[Clan]

Originally Posted by GrantV50

On short stretches, we should be looking at increasing to 100MPH. Modern cars are capable of this speed, and braking from this speed.

Unfortunately the human brain isnt ...

[Clan]

Originally Posted by biggbn

Name me a car that gets better mpg at 70 or 80 than 60? Anecdotal evidence of the over 200 i have owned and countless I have begged, borrowed or stolen suggests...none. You may have evidence that suggests otherwise and thus contradicts every roadtest and manufacturers figure, or owners review I have ever read or heard about?

Edit, sorry Dave that sounds quite confrontational. Didn't mean it that way, just curious what you mean? Even my frugal wee mini will get over 70mpg at 60 and high 50s at 80?

There is a massive increase in air resistance over 60 mph it goes up in a non linear way , double the speed and you get 4 times the wind resistance .

[Laird Scooby]

Originally Posted by biggbn

Name me a car that gets better mpg at 70 or 80 than 60? Anecdotal evidence of the over 200 i have owned and countless I have begged, borrowed or stolen suggests...none. You may have evidence that suggests otherwise and thus contradicts every roadtest and manufacturers figure, or owners review I have ever read or heard about?

Edit, sorry Dave that sounds quite confrontational. Didn't mean it that way, just curious what you mean? Even my frugal wee mini will get over 70mpg at 60 and high 50s at 80?

Honda Elysion

Honda Accord 3.0

Rover 827

Just 3 to start the ball rolling. Maybe it's a Honda thing...............

No apology needed George as no confrontation sensed! I know what you're saying and in many ways i agree, for example my 760 doesn't abide by this rule and is thirstier at (indicated) 78mph than at 66mph (True speeds via GPS - 70 and 60mph)

However on a recent longer trip of ~130 round trip, mainly dual carriageway at 78mph indicated and cruise controlled, it returned ~29mpg. This is much better than the 20-23mpg it returns on noral use where it rarely gets above 30mph - maybe the 760 does subscribe to being more efficient at motorway speeds!

[biggbn]

Originally Posted by Laird Scooby

Honda Elysion

Honda Accord 3.0

Rover 827

Just 3 to start the ball rolling. Maybe it's a Honda thing...............

No apology needed George as no confrontation sensed! I know what you're saying and in many ways i agree, for example my 760 doesn't abide by this rule and is thirstier at (indicated) 78mph than at 66mph (True speeds via GPS - 70 and 60mph)

However on a recent longer trip of ~130 round trip, mainly dual carriageway at 78mph indicated and cruise controlled, it returned ~29mpg. This is much better than the 20-23mpg it returns on noral use where it rarely gets above 30mph - maybe the 760 does subscribe to being more efficient at motorway speeds!

My accord 3.0 auto got 34mpg average at 60mph round trip and only 27mpg at 70mph? It was the coupe, wonderful, wonderful car but the price of parts!!

Re 760, all cars are more efficient at steady speed than stop start driving. I always get better mpg than people think, lexus ls400, 34mpg commuting, saab 93 2.8v6 manual, 40mpg plus...stay away from towns and stick the cruise on just below 60mph as that has always proved the best compromise

[Laird Scooby]

Originally Posted by biggbn

My accord 3.0 auto got 34mpg average at 60mph round trip and only 27mpg at 70mph? It was the coupe, wonderful, wonderful car but the price of parts!!

Re 760, all cars are more efficient at steady speed than stop start driving. I always get better mpg than people think, lexus ls400, 34mpg commuting, saab 93 2.8v6 manual, 40mpg plus...stay away from towns and stick the cruise on just below 60mph as that has always proved the best compromise

I explained further up the thread somewhere about my 827, 2 trips to the same place, 2 consecutive evenings, similar weather and traffic conditions, first night kept the speed to 70-80mph, 40mpg, second evening, 80-90 and returned 43mpg.

As for the 760 recently, i suspect i could easily have bettered the ~29mpg on that trip if two things were done.
First, if i'd known the CO had crept up to 1.88% @ idle i could have tweaked it down a lot, second if the muppets in the inside lane at 58 mph had been taught to drive, specifically overtake. They would move out without signalling then sit there at 58.1mph taking forever to get past the vehicle they were trying to overtake then glared daggers at me as they pulled back in. It wasn't my fault, they were the ones driving badly! The queue of traffic behind me all confirmed my thoughts and glared daggers at said muppet as they all went past them.

In other words, if i could have maintained a steady speed, it would likely have done better and better still if it hadn't been running rich.

[tofufi]

Originally Posted by Laird Scooby

I explained further up the thread somewhere about my 827, 2 trips to the same place, 2 consecutive evenings, similar weather and traffic conditions, first night kept the speed to 70-80mph, 40mpg, second evening, 80-90 and returned 43mpg.

A couple of single trips don't really cover everything that is going on there though... Some days my Volvo 740 will get 40mpg, others it's 50 (though it normally hovers around 44-46) on ostensibly similar journeys.

The difference between 60mph and 70mph is 17%. As drag is proportional to the square of the speed, 70mph has 36% more drag than 60mph. You'd need the engine to be a lot more efficient at 70mph than 60 to make the car use less fuel per mile.

I've never come across a car where the efficiency genuinely rises the faster you go, above (say) 50-60mph.

Plenty of anecdotal evidence to back that up here:

https://ecomodder.com/forum/showthre...you-15182.html

[Laird Scooby]

Originally Posted by tofufi

I've never come across a car where the efficiency genuinely rises the faster you go, above (say) 50-60mph.

There is a genuine reason, variable length inlet tracts that just happen to shorten at 3800-4200rpm to increase efficiency which just happens to be the higher speed on the road.

[tofufi]

Originally Posted by Laird Scooby

There is a genuine reason, variable length inlet tracts that just happen to shorten at 3800-4200rpm to increase efficiency which just happens to be the higher speed on the road.

Fair enough. Given that 99% of cars on the road won't have that, reducing speed limits to 60mph on motorways would still reduce fuel consumption and CO2 emissions.

[Laird Scooby]

Originally Posted by tofufi

Fair enough. Given that 99% of cars on the road won't have that, reducing speed limits to 60mph on motorways would still reduce fuel consumption and CO2 emissions.

Are you sure about 99%? I believe the x90 has a similar system on the B6304 engine, fairly sure a lot of later Volvos have it, a lot of Hondas, many Vauxhalls have it (Senator 3.0 24v with "Dual Ram") and countless cars out there have VVTi, VTEC or similar which alters the valve timing and/or introduces the second set of valves on each cylinder above certain speeds - all of which achieves a similar result.

That's millions of cars Jim, all with either variable length inlet or variable valve timing and lift that improve the engines efficiency at higher rpm.

With that in mind, it would therefore make sense to increase the speed limit and encourage people to drive faster to get their engines into the optimum range of designed operation.

Also some engines will drop cylinders out completely when cruising above certain speeds and then the economy really shoots up and the emissions drop.