Most Economical Speed To Drive?

[smoky2004]

Hello, I drive a 2004 Avensis 1.8 petrol Auto which also runs on gas. What is the most economical speed to drive at on the Motorway to get the most miles from the fuel?

[Uncle Buck]

A reasonable compromise between speed & economy on motorways would be 60 mph - not less than this or you'll just annoy HGV drivers.

[FROSTYBALLS]

Yes - 60'ish.

We had a 2000 Honda Civic 1.4 - any speed 70 and upwards and the economy was awful

[smoky2004]

Is there much difference in fuel consumption at 60mph compared to 70mph?

[Sprinter2012]

Is there much difference in fuel consumption at 60mph compared to 70mph?

The short answer is yes, air resistance increases exponentially as your speed gets higher.

So you could end up dropping fuel economy by up to 20% just for those extra 10mph.

[Mike169]

If you sit on the inside lane with all the artic trucks and do their speed you'll achieve your maximum mpg and officially they are regulated at 56mph or just a tad more so as long as you don't keep trying to be overtaken by the truckers but more like do their speed you'll be doing ok and achieving your optimum economy.

Mike.

[Cyker]

I like to follow NatEx coaches; Them things really haul! :)

Avoid major supermarket chain lorries like Sainsbury, Tesco, Asda etc. as they seem to run slower (The problem is it's the cabs, not the trailers that you need to check!). Stobarts are usually pretty quick. Artics from outside the UK are usually going quicker than they should ;)

I've been playing around with different speeds over the past few months, and I think the biggest factor is acceleration - I have been finding I'm consistently getting ~5mpg better doing 70mph than at 63mph and the only reason I can think of for this is that I can run at 70mph for looong periods of time, whereas at 63mph I run into lorries and have to overtake them, which I will accelerate to 70mph to do so I can get back into the left lane ASAP, and I reckon it's that acceleration that is bringing down my mpgs.

(The only other possible reason i can think of is that 70mph is right slap bang in the middle of the 1.4D4D's maximum torque zone (Which is basically from ~1800rpm to ~3000rpm) whereas 63mph is just at the bottom of it)

[Uncle Buck]

Yeah, there are exceptions to the rule. My Nissan Almera achieved better MPG at 70 mph then at 60 mph - presumably down to the gearing. This doesn't sound likely, but I proved it again & again over several years. However if I tried anything slightly above that speed, then the fuel would disappear much more quickly.

As stated before, MPG is heavily affected by drag at motorway speeds, so an old Jeep would get very poor figures (even with a modern engine) - while a new Civic for example would slip through the air much more efficiently.