optimum speed for best fuel efficiency

[spn221]

Hi

For a regular commute to the grocery for a 6 mile trip, I have two options.
1) The dual carriageway
2) "A" road with max of 40mph

I was wondering if there are some general guidelines or rules which I can use.
My 10 year old Avensis does not have a reliable trip computer, so I am more basing on general ideas.

In general which would use more fuel a 6 mile trip @ 60mph (optimum speed for best milege) even though max possible is 70 on a dual carriageway or doing 5 miles on a A road with a max speed of 40 mph?

Thanks in advance

Regards,
sn

[Gareth]

There are a number of factors so it is difficult to provide specific guidance but there are some general principles that might help.

One is that increasing speed above a certain point has a big adverse effect. A wikipedia article explains and has more useful information.

Another is that you want to avoid slowing down as much as possible, since it there that fuel is 'wasted'.

For such a short trip I'd have thought that the time for the engine to warm up might be a significant factor as well.

[spn221]

thanks Gareth.
Yes, true, that is why I avoid car for short journeys upto a mile which I can cover with a cycle or walk.
So, it looks like I have to experiment and no ready answers.
May be I have to look at some Avensis forums to see if someone has already done the experiment.
Thanks for the pointers.

[jameslb101]

I don't think any trip computers are that reliable so why not test it manually yourself. If there is a petrol station very close to one end of your journey start there, fill up, and do the round trip on the A road, then fill up again and do the round trip on the DC, then fill up again. See which cost more from your last two fills ups and you'll have an answer.

Even if you did the 7 mile DC trip at a conservative estimate of 40mpg, it'd only cost about £1.10, so I think the difference between the routes wouldn't be more than a few pence anyway.

[Horse]

The effect of other traffic - eg HGVs owith limited speeds r buses stopping may also be a major influence.

Other than that, 'eggshells on the pedals' and really good planning to avoid braking may be your best friends. Oh, and not warming the car to clear frost ir condensation [NB I'm obviously not saying 'Don't clear your windows' ]