What's the ideal speed for max mpg?

[Gman1978]

Hi,

Just wondered..

I have a fabia II 1.9 tdi, and if I cruise gently around town/country @ 30-40mph I get up to 70.6 mpg on a 30 mile trip (so far).

I wonder if there is any given sweet speed to maximise mpg?

I suppose if I were to find a perfectly flat road, with no wind, fifth gear, then set cruise control to 30, then go up in increments until I see the max reading on the real time mpg, would that work? (There is probably no public road like that in surrey)

I've searched the forum (the wait seconds before another search is a pain) but couldn't find the answer.

I would assume that each model would have an idea speed? would that be the makings of a list?

[Babs]

Each car has it's ideal speed, as it'll be a combination of engine efficiency, drag (aerodynamic and rolling resistance) and weather conditions!

Like my Octavia is better at 85mph than it is at 60mph, for example.

[Kiwibacon]

Carefully monitoring your real time fuel readout should help you work that out.

[petrolbloke]

Each car has it's ideal speed, as it'll be a combination of engine efficiency, drag (aerodynamic and rolling resistance) and weather conditions!

Like my Octavia is better at 85mph than it is at 60mph, for example.

Sounds unlikely unless you're not in 5th gear at 60mph or you have a strange remap.

But yes it depends on lots of things - engine, gearing and aerodynamics being the main ones. For most cars it's probably in the range of 40-60mph.

[Phil-E]

Each car has it's ideal speed, as it'll be a combination of engine efficiency, drag (aerodynamic and rolling resistance) and weather conditions!

Like my Octavia is better at 85mph than it is at 60mph, for example.

I have to agree with that really after having done several long journeys doing speeds of 80-90 and then trips to Germany going flat out (amazing how the miles tick by at 129mph).

Obviously I think 120+ is probably going to have a negative effect

If I drive 60 mph in my car it does worse. 70mph and I have 1900rpm and it starts getting getter. About 2000-2100 rpm seems the sweet spot (80ish).

Phil

[Latte]

My wheels are severely out of balance too. The dashboard vibrates that much that it's blurred.

It only comes into focus above 124 mph, that's the sweet spot.

I successfully used this as my defence for doing 130 through the shopping centre.

I got the sentence down to 8 years!

On the plus side, the cars infinitely more economical now it's stood rusting.

[Aspman]

Doesn't take much to keep a car going, you're only using petrol to fight against wind resistance and friction.

So the perfect speed for perfect economy on a perfect road depends on the wind velocity and the friction : rpm in your engine.

In the real world the closer you can make your drive to the perfect conditions the closer you'll get to max economy.

So as few hills and corners as possibly (uses energy to go up and turn (changing direction is a form of acceleration)), as steady a speed as possible (lots of energy to accelerate), and foot off the accelerator when braking / going downhill (modern engine doesn't use fuel in those circumstances).

You can research hypermiling tool all they really add are more dangerous things you can't really use in the real world like drafting.

[Babs]

Nope, completely standard car, my previous one did the same. It's all about efficiency in the engine.

[cheezemonkhai]

88mph... then you can go back in time to a point where fuel is cheap, fill up for peanuts and not have to worry

Might need a small mod to the car first

[Lofty79]

most cars i drive are best once in top gear as slow as you can go without labouring the engine

[JezF1000]

Biggest difference is aircon, I'd be astounded if any car was more economical at 85 as opposed to 70.

57.7mpg back from Warwick today on a standard PD170 -very happy with that!

[KenONeill]

88mph... then you can go back in time to a point where fuel is cheap, fill up for peanuts and not have to worry

Might need a small mod to the car first

This link may help - www.andyspares.co.uk/mr_fusion

[Phil-E]

Biggest difference is aircon, I'd be astounded if any car was more economical at 85 as opposed to 70.

57.7mpg back from Warwick today on a standard PD170 -very happy with that!

Our aircon is always on (climate so never bother turning "Econ" on).

And you can't really complain at that economy. Not when you have all that power to play with too should you need it.

Phil

[JezF1000]

Our aircon is always on (climate so never bother turning "Econ" on).

And you can't really complain at that economy. Not when you have all that power to play with too should you need it.

Phil

MPG so far has exceeded expectations, 50.8 average over 1700 miles of mixed driving.

I do drive with aircon off where I can though as it makes a big difference to MPG and I don't like sitting in aircon for long periods of tie unless it's really hot.

I actually think all cars should start in economy mod on CC - would probably save millions of tonnes of CO2 a year.

[Babs]

I actually think all cars should start in economy mod on CC - would probably save millions of tonnes of CO2 a year.

But what will the plants eat?

[cheezemonkhai]

But what will the plants eat?

humans?

[JezF1000]

Hopefully slugs in my bloody garden!

[VladSoilerOfCarpets]

0mph.

Then it's using no fuel at all...

[Lofty79]

0mph.

Then it's using no fuel at all...

Yes but 0mph is also 0mpg so by definition the worst speed to get best economy hehe

[Babs]

But if the engine is switched off... you won't be using fuel... hmmm....

And then all the trees will die!

[mdon]

It's generally about 50-60mph.

[Gumby]

Used to find my old 1.2 would shoot up to 50 odd MPG when dong a constant 60mph, 70 would make it drop down to 38MPG.

Never really paid attention on my vRS, it's just too much fun to really bother about MPG!

[devonutopia]

Sweet spot in mine seems to be smack on 70mph in 6th gear. Any slower and the engine feels laboured (70mph = 1800 rpm) and any faster you need more juice to maintain speed as the car is as aerodynamic as a brick!

[faboka vrs]

50-60 here. Managed 73mpg on a 20 trip on a/b roads.

I find 1600rpm good. Must be in a good BSFC zone.

[Phil-E]

Sweet spot in mine seems to be smack on 70mph in 6th gear. Any slower and the engine feels laboured (70mph = 1800 rpm) and any faster you need more juice to maintain speed as the car is as aerodynamic as a brick!

Must be why mine does well at high speeds. The Cordoba is more aerodynamic than the Fabia... only just