Does it affect mpg?

[Adz]

Originally Posted by PLANK

sadly lorries aren't built for fuel efficency and aerodynamics at all! they are built for the largest volume of truck within the legal maximum dimensions, that's why they have a slab flat front and the driver sits over the engine.

I beg to differ when the Scania & Volvo bull nose's are on the road.!

[(RIP) PLANK]

Originally Posted by Adz

I beg to differ when the Scania & Volvo bull nose's are on the road.!

beg all you like it's still true, they have to meet the size criterea, the trucks you mention are obvioulsy more aerodynamic, but the scania you quote i believe is the model that - with maximum lenght trailer - becomes over the limit, but scania decided to put it into procduction anyway.

I looked into this in depth recently when researching for a book (if you remember i started this by asking for hints and pointers on here, and you helped me out). I don't have tome to drag it all out now, but i do have it all in print.

I may have got the exact models wrong, but trucks are built for capacity not aerodynamics, of course it is a compromise, and there will be minor sacrifices to one or the other, hence the range and choice of trucks - but not much!

It was a trend started in by the Reanault Magnum, max size in a given space, the design saw off most of the competition and the rest followed suit. It's now an interesting piece of road haulage history.

[Adz]

Originally Posted by PLANK

beg all you like it's still true, they have to meet the size criterea, the trucks you mention are obvioulsy more aerodynamic, but the scania you quote i believe is the model that - with maximum lenght trailer - becomes over the limit, but scania decided to put it into procduction anyway.

I looked into this in depth recently when researching for a book (if you remember i started this by asking for hints and pointers on here, and you helped me out). I don't have tome to drag it all out now, but i do have it all in print.

I may have got the exact models wrong, but trucks are built for capacity not aerodynamics, of course it is a compromise, and there will be minor sacrifices to one or the other, hence the range and choice of trucks - but not much!

It was a trend started in by the Reanault Magnum, max size in a given space, the design saw off most of the competition and the rest followed suit. It's now an interesting piece of road haulage history.

Its not over length & doesn't need CAT 1 / 2 / 3 & is legal FACT

They way they got round it for the UK market was to only put the 4 wheel tractor units on sale in the UK & then Volvo followed suite.

You will see more bull nose recys & where there more commonly used as the Dutch do many & various axle conversions & the bull nose models in general had bigger engine options.

[Thomas-the-Terrano2]

ws under impression that in uk specs, not europe, it was an issue to haul
full size trailer with a yank tractor unit, but that scania is quite a short
bonnet and ive seen several hauling 40'ers, may 45's, look good but given
choice would keep the wheelbase of the tractor and have more sleeper
cab over engine, ie double bed plus behind seats. kenworth aerodyne style.

[briggie]

[Adz]

Originally Posted by Thomas-the-Terrano2

ws under impression that in uk specs, not europe, it was an issue to haul
full size trailer with a yank tractor unit, but that scania is quite a short
bonnet and ive seen several hauling 40'ers, may 45's, look good but given
choice would keep the wheelbase of the tractor and have more sleeper
cab over engine, ie double bed plus behind seats. kenworth aerodyne style.

All flat cabs with i.e. Scania Topline are double bunked

[Adz]

Originally Posted by daved

I usually leave my roof bars (not the rails that run the length of the car theyre bolted on i mean the bars that go cross ways) on all the time, its handy and Im too lazy to take them off

Has any one doe the maths to work out just how much extra fuel you use if you leave roof bars or roof racks on I know it does , just not how much

Originally Posted by extreme-4x4

just one i found quickly . http://www.metrompg.com/posts/roof-racks.htm

not over interested in an argument over it .... i dont like lights or shite on the roof anyway.

Back on topic

http://fuel-economy.co.uk/indepth1.shtml

[extreme-4x4]

Originally Posted by briggie

love it

[zippy656]

yep great..

[Thomas-the-Terrano2]

double horizontal, not vertical

[extreme-4x4]

Originally Posted by Adz

It will cause drag & noise maybe That is a FACT (not taking the P)

As for altering the MPG its a load of tosh

My mav when i 1st got it avaraged 300 miles on a full tank

My mav now with 33's / roof bars with 4 waffle boards / snorkel / lights . . .
Yep . . . . . Still 300 miles averaged

yes very


the following taken from your own link


Its not just windows that will cause drag either! Listed below are some steps that will help reduce drag.

• As mentioned above, when travelling at speed close your windows and sunroof.
• If you are lucky enough to be driving a convertible in the summer, stop and put the roof up (provided its safe to do so) before you drive on motorways or fast A roads.
• Remove any roof-racks, roof-boxes or bike racks when you aren't using them. These are some of the worst offenders when it comes to drag!
• Its great to support for the national team, but remember to remove your England flag from your car when the matches are over.
• If your car's bonnet is covered with dead flies and lumps of mud and goodness knows what else, wash your car! It may seem like a pretty pointless thing to mention, but all those extra lumps and rough edges will disrupt the airflow passing over your car, causing more drag. Oh and everyone likes to see a shiny motor!

[rustic]

Originally Posted by daved

I usually leave my roof bars (not the rails that run the length of the car theyre bolted on i mean the bars that go cross ways) on all the time, its handy and Im too lazy to take them off

Has any one doe the maths to work out just how much extra fuel you use if you leave roof bars or roof racks on I know it does , just not how much

It would depend on how aerodynamic the car was in the first place, cars designed to give the greatest fuel economy will be greatly affected by any thing that spoils the smooth flow of the air over the car.
The effect of drag is not linear, twice the speed doesn't create twice the drag, it can create 2x2 ie 4 times the drag. So aerodynamics is more critical at high speeds.

Landies which are as aerodynamic as a house brick, won't be greatly affected by 4 roof mounted spot lights at 50 mph.
However an economical low drag car will be greatly affected by even a window slightly open, and certainly a roof rack will cause turbulance, noise and heat caused by the friction, the energy has to come from some where, ie the fuel.

In a word, you will be using more fuel, how much as stated in the previous threads, depends on speed as well.


What I never understood is that tin box towers used to have the roof mounted wind deflectors, that at the correct angle could save fuel at a particular speed.
If this was tested at say 60mph in a wind tunnel, drag could be reduced considerably, but they were fitted in the wrong place, the wrong angle, but worse than that, they drove around on their holiday with it still fitted to the car, burning all the fuel that they might have saved on the journey to and from the holiday location.

As an example, we drive the Picasso on long journeys, and occasionally we tow a small 5x3 camping trailer, even with little weight in it, the fuel economy falls from 55 mpg to well below 50 mpg.
Caused by the turbulance and drag of the trailer.
We try to fit everything into the car where possible.

To test out the drag, try putting your hand out of the window at 20 mph or even more...
WARNING: May cause injury, so take care..

[Fez_uk]

it will effect it but to say exactly how much is difficult.

But my opinion is surely it can't effect it much. Maybe 1mpg less?

[BigBlack]

Originally Posted by Fez_uk

Maybe 1mpg less?

To look at it a different way then...


10,000m @ 28mpg = 357.14g / 1623.59ltrs @ £1.30p/ltr = £2,110.67
10,000m @ 27mpg = 370.37g / 1683.73ltrs @ £1.30p/ltr = £2,188.84

So... extra £78.17 per year.... or roughly 60ltrs of fuel!


ps: ok, I know most dont get 28mpg.... but rough estimate!

[extreme-4x4]

well, as you know mine is trimmed a lot but still got the original bumpers on just trimmed in the places i think best.
i recon with the bigger tyres only 31's at the mo i save around 3 mpg.

i dont have any data or facts / proof . but thats what i recon i save . and i suppose like everyone else trying to save a bit here and there .

i could be right and saving 3mpg or i could be wrong and blindly suffering some kind of placebo effect .... but unlike the people who do leave the roof bars on or loads of other crap in the way causing drag ..... i still get a warm feeling thinking im saving some dosh