Most Economical Motorway Speed?

I think it's fairly easy to "feel" where that sweet point is, particularly on a bike- striking that balance between low rpm and minimal throttle input. The SV cruises gleefully at around 70mph with the merest fraction of throttle in top gear, crank it up by 20mph and the difference is noticeable. It'll do it of course, but not as eagerly.

Similarly much slower than 60 in 6th gear and it's asking you to downshift (at least mine is ).

(Standard gearing K4 S).

Originally Posted by Spiderman

I was told by a very knowledgeable man once that when the fuel was low I should not worry too much about my top speed when getting home as it was hard accelaration that ate the fuel, not a high top speed.

I kinda agree from experience. Acceleration is the fuel killer....

Bu then when your at speed, your not on the throttle, but the explosion still happens (hence air n fuel going in).

Rolling off throttle, esp downhill doesn't use fuel, the engine momentum turns the engine over, not the fuel.

But, if i sit at 110mph, or 70mph, doing 11-mph uses a hell of a lot more fuel.. So when running low, i sit at 60mph as i know it'll get me vastly further than sitting at 80mph....

No other proof other than my own experience form running out of fuel a few times and doing about 50,000 miles in 4 years on bikes

I always believed it was lowest throttle angle. Hence less air, hence less fuel. All cars and must be the same for bike have an optimum air to fuel ratio for economy norm 15:1 and performance norm 12.5:1 reguardless of rpm. Cars are normally mapped for economy at constant throttle angles and this is were the lambda probe comes in to hold 15:1(do k8's etc have better consumption?). Under hard acceleration that goes out the window and the car will use the map for optimum perfomance. Also when deaccelerating the throttle valve is shut and the engine stops fuel and air and uses momentum to slow down. So it's better to use engine braking than coasting downhill.
As to the best speed on a motorway not a clue, guessing the lowest throttle angle you can achieve in the highest gear. But that will vary will drag and incline. You should pick up speed going down a hill so you need to use less throttle going up, but you'll slow down when you go up. This is a reason why I find cruise control in cars so poor on fuel.

Just as a point of order:

56mph isn't the point at which a car/bike/bus whatever is running most efficiently, simply one of the speeds at which economy is tested, and quoted, in order to ensure that everything is compared like-for-like.

The most economical speed is that which a vehicle of any kind can maintain using the lowest rpm for any given gear without causing the engine to struggle, which is generally around about the point at which peak torque is produced.

[ophic]

Originally Posted by Dan

JThe most economical speed is that which a vehicle of any kind can maintain using the lowest rpm for any given gear without causing the engine to struggle, which is generally around about the point at which peak torque is produced.

Not on a petrol engine - most produce peak torque way up the rev range. The engine shouldn't struggle until it gets down near tickover, which is nowhere near peak torque at all.

Most normal petrol engines, in cars, produce peak torque around 3000-3500rpm, unless you have some silly little Honda which produces peak torque at 7800rpm... vtak kicked in yo...

[ophic]

Originally Posted by Jamiebridges123

Most normal petrol engines, in cars, produce peak torque around 3000-3500rpm, unless you have some silly little Honda which produces peak torque at 7800rpm... vtak kicked in yo...

and they redline at 5-6k? and will still pull at 1200? certainly not starting to struggle at anything lower than peak torque.

Varies from bike to bike. I read some magazine (damned if I can remember which) that asked the same question and tested it with a Fireblade and a BMW GS - the CBR was actually more economical than the BMW when revved hard purely because the engine was tuned for top-end power rather than the middle of the rev-range, like the BMW.

Originally Posted by ranathari

Varies from bike to bike. I read some magazine (damned if I can remember which) that asked the same question and tested it with a Fireblade and a BMW GS - the CBR was actually more economical than the BMW when revved hard purely because the engine was tuned for top-end power rather than the middle of the rev-range, like the BMW.

thats like the test top gear did, with a bmw 5 series or something and a small town car and they both drove around the track at 80/90mph and as the small car was using fill power to maintain the speed and the bm was just ticking over the bm went a couple of miles further than said small car on a gallon of petrol, conclusion buy a big car, haha.

Originally Posted by ophic

and they redline at 5-6k? and will still pull at 1200? certainly not starting to struggle at anything lower than peak torque.

If you put your car in 5th and try to pull at 1200, unless you have a larger engine or something, it'll jump and studder a little