Most Economical Motorway Speed?

[STRAMASHER]

If I want to stretch out a tankful I will sit at 65-70 (Usual 80mph).

Big difference in consumption. And still safe and not causing an annoyance.

Got me to the magic 200 mile on my GSX14 from a 22ltr tank with juice to spare.

Only the once mind. I love getting happy on the throttle.

[ophic]

Originally Posted by Jamiebridges123

The most economical speed for any vehicle would be where the engine produces the most torque...

Got any explanations to back that up?

[Spiderman]

Originally Posted by Brettus

Will be interested to see if someone does come up with a decent answer though, I've often wondered what it was, well usually when I'm on a motorway with the fuel light flashing

PMSL, to be honest mate i thought it would be you after i saw this post from you in another thread...

Originally Posted by Brettus

Sorry, bit too geeky but my stats collected over the course of a year average out at:
SV650s Sport K6

Fill up: £13.99 (bear in mind that covers when petrol was at 120p +)
Fuel price: 105.1p
litres: 13.8 (so I've usually had around 3.5 left in it)
MPG: 55.1
Miles between fuel stops: 170.4

Pence Per Mile:
Fuel: 9p
Tyres: 2p

Average miles per tank: 206.3 (assuming by calculation that I ran it to empty)

Reserve Capacity:
Flashing (4.5L left so I was told) 54.6 miles
Solid (1.5L left) 18.2

I will usually risk 2-3 trips to work (each way not both) from when it starts flashing and I've not run out yet. closest I got was 1.11L left.

Only twice have I managed to make the bike to less than 50mpg, I got 44.5 on one fill up and the tank would only have got me 166 miles then.

But i'm glad to see its not an obvious answer and i'm not the only one whos wandered it either.

I agree in principle of course with what most of you have said, excpt for Quiff of course, but i'd love to see a calculation proving a certain speed in MPH cos its obviosuly a lot of factors that can change it, like headwind or tailwind etc.

I''m sure the combined talents of the Org will mena there is someone who will know...or can work it out.

Originally Posted by ophic

Got any explanations to back that up?

Read it in Autocar ages ago.

[ophic]

Originally Posted by Jamiebridges123

Read it in Autocar ages ago.

Not saying its wrong, just would like to hear the theory behind it before I believe it.

I'd guess it's because the engine will "pull" the best, IE you'll need less throttle to go up a hill ETC, basically it just has the most available pulling power with the minimum of throttle input

[Spiderman]

Originally Posted by Jamiebridges123

The most economical speed for any vehicle would be where the engine produces the most torque, which in most cases is around 3200rpm in cars, which in general, depending on type of car, is between 55 and 70mph, so hence why most people take 60 to be a good general rule of thumb.

On the SV I just keep to 60 as it's a lovely and rounded 4500rpm.

This kind of stuff is just generalisation tbh, which is fair enough when it comes to car engines i guess as they are mostly the same layout.

I wanna know specifically for an SV with its own engine charachteristics what would be the optimum speed cos i'm certain that its not the same as a car!

[ophic]

Originally Posted by Jamiebridges123

I'd guess it's because the engine will "pull" the best, IE you'll need less throttle to go up a hill ETC, basically it just has the most available pulling power with the minimum of throttle input

but say peak torque is 7krpm - lets say thats 70mph for easy figures

at 35mph in top gear, the engine may be less efficient but the drag on the vehicle has dropped by a factor of 4, so unless the engine is 4 times less efficient at 3500rpm than 7000rpm (which i doubt) then you'll go further on the same fuel at 35mph.

[ophic]

ah-ha i've spotted my own error - the drag is 4x less but the vehicle has to push through it for twice as long. So the engine only has to be 2x less efficient at 3500rpm - i still doubt that its the case.

I got 155 miles on 10 liters at between 60 and 75mph with some occasional full throttle bursts riding back from Yorkshire..

So on the SV I'd guess about 60-70 would be fine!