Fuel Economy Reporting Thread

magneto

A recent research found that most car engine run most efficient at 50 -70 miles per hour.

xtreem_2

You should never have to fill up at a motorway service station. Here is a free to use map http://www.thegreatmotorwaysecret.com/map1.htm
which shows all the superstores near to motorway junctions in England and Wales.

jeferey

tomstickland wrote: »

I was reading What Car whilst waiting at the dentist. The Aug 08 issue has a report on mpg, including detailed measurements. All of the vehicles tested produced better mpg as speeds were reduced, with the best results at the lowest speed that they tested at, which was 40mph.

I have finished my experiment and driven for a complete tankful of diesel at much slower than normal speeds. I've been on the motorway for about 20% of the time, the rest A roads and the dreaded commute to Sheffield. On the A57 I have been doing about 40-45mph (50 limit) and 56 on the m-way (slow I now but I've actually found very little difference in journey times - it's amazing how many people overtake you and then you catch them up at the next lights!).
Result: previous average: 46mpg (official stats for my car 44.9mpg Honda FR-V 2.2)
Average for this tankfull: 55mpg - an amazing 623.3 miles on one tank (51.51ltrs)
I will do the same for the next one to double check, but I know for a fact that if I drove everywhere at 70mph I do not get anywhere near this fuel consumption.
Has anyone else tried this - have a go and let us know if not.

AdrianHi

jeferey wrote: »

I have finished my experiment and driven for a complete tankful of diesel at much slower than normal speeds. I've been on the motorway for about 20% of the time, the rest A roads and the dreaded commute to Sheffield. On the A57 I have been doing about 40-45mph (50 limit) and 56 on the m-way (slow I now but I've actually found very little difference in journey times - it's amazing how many people overtake you and then you catch them up at the next lights!).
Result: previous average: 46mpg (official stats for my car 44.9mpg Honda FR-V 2.2)
Average for this tankfull: 55mpg - an amazing 623.3 miles on one tank (51.51ltrs)
I will do the same for the next one to double check, but I know for a fact that if I drove everywhere at 70mph I do not get anywhere near this fuel consumption.
Has anyone else tried this - have a go and let us know if not.

Back in August 2000 when the refineries were blockaded in protest for petrol going above about 90p per liter I think it was, I drove my Mitsubishi Galant 2.5L V6 at 56mph on a trip up the M40 London - Birmigham. The motorway was full of people doing the same thing at the time. On a trip like this I would normally see 32-33mpg, I got 38mpg on that tank!

I've seen other speed and fuel consumption tests which agree with the 40mph rule, which is a little strange as even cars with a 6th gear which cannot be used under about 50mph are still a tiny bit more economical at this speed.
Interesting thing about this test is that different cars fuel consumption increases at different rates as speeds rise to the point where some quite powerful big engined cars become more economical than cars such as the Prius, Vauxhall Zafira 1.9 diesel etc. at these higher speeds.

jeferey

AdrianHi wrote: »

...I've seen other speed and fuel consumption tests which agree with the 40mph rule, which is a little strange as even cars with a 6th gear which cannot be used under about 50mph are still a tiny bit more economical at this speed.....

I can drive in 6th gear at 30mph in my diesel Honda as long as it's flat or downhill - does not straining engine. At 40mph, 6th is fine up and down hills but I do accelerate slightly going down hill and ease off slowly going up - seems to help economy as well.

AdrianHi

jeferey wrote: »

I can drive in 6th gear at 30mph in my diesel Honda as long as it's flat or downhill - does not straining engine. At 40mph, 6th is fine up and down hills but I do accelerate slightly going down hill and ease off slowly going up - seems to help economy as well.

What RPM at 70mph in 6th?

jeferey

AdrianHi wrote: »

What RPM at 70mph in 6th?

Next time I go that fast I'll check ( lol ) - I think it's about 1900

AdrianHi

jeferey wrote: »

Next time I go that fast I'll check ( lol ) - I think it's about 1900

I'm just trying to understand how high a gear 6th actually is to be usable at these speeds.

jeferey

AdrianHi wrote: »

I'm just trying to understand how high a gear 6th actually is to be usable at these speeds.

No problem Adrian. I think the kind of engine as well as the gearing makes a big difference to whether you can use 6th at low speeds. Chap I know has a 2.0 petrol A3 and he can't use 6th in his below 45. Diesels seem better suited due to their power band being lower generally and also the greater torque which tends to kick in low down as well.

AdrianHi

jeferey wrote: »

No problem Adrian. I think the kind of engine as well as the gearing makes a big difference to whether you can use 6th at low speeds. Chap I know has a 2.0 petrol A3 and he can't use 6th in his below 45. Diesels seem better suited due to their power band being lower generally and also the greater torque which tends to kick in low down as well.

I'm comparing with my BMW 320d 6 speed manual. On the flat at an indicated 47/48mph you can just about accelerate, but it's really not happy below indicated 52mph = 1400/1500rpm. 40mph in 6th is something you only do downhill if at all.
On the flip side you can drive all day at an indicated 85mph and still return 48mpg+ as the revs are so low. Indicated 70mph is about 1900rpm.