Does it affect mpg?

[Adz]

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 :thumbs

 

[Adz]

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 :nenau

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 :nenau

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 :augie

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

 

[extreme-4x4]

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love it

 

[zippy656]

yep great..

 

[Thomas-the-Terrano2]

double horizontal, not vertical

 

[extreme-4x4]

It will cause drag & noise maybe :nenau 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 :thumbs

yes very :augie:augie:augie


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]

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 :nenau

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 :nenau

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. :thumbs


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. :nenau
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. :doh

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.:doh
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]

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! :thumb2

 

[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

 

[(RIP) PLANK]

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.

look, this is going way off course, i reffered to one specific scania model circa 1990, not current models, so your point is missing the point! The point is tractor units are not the most aerodynamic vehicles on the road and are designed for overall capacity not fuel efficency - that was my point and it is still very true.

For example, take a given truck and through an aerodynamic cab profile increase the fuel efficency by 10% and in doing so reduce its overall load capcity by 10% you now need 11 loads were there were 10 so 10% more trucks on the road and 10% more fuel used, not gains whatsoever.

in these new fuel efficent times economy will drive design, but only to an extent it will allways be a compromise;

my point in short:

Whatever you bolt to your roof will afect fuel economy - full stop.

and comparing it to a huge pantechnicon will not help!

Now lets get back on topic :thumbs

 

[(RIP) PLANK]

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

spot on :thumb2

 

[Deleted account DD]

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

the one I was in yesterday wasnt :augie

 

[Deleted account DD]

Definitely getting less mpg on mine on a mixed driving cycle with the supposed "aerodynamic" roof bars fitted.

Theres absolutely no dount that anything that disrupts the airflow will affect consumption. May be so neglible you wont know it I suppose.

Thanks for the input, i posted the question before I logged off for the night and I cant believe the number of replies :lol:lol:lol

 

[extreme-4x4]

what you mean is you planted the seed before logging off, then left it for all the following inevitable disputes.

:augie:augie:augie

 

[Deleted account DD]

what you mean is you planted the seed before logging off, then left it for all the following inevitable disputes.

:augie:augie:augie

:augie

no wouldnt do that.

I just suspected there may have been someone had worked it out, I know it does affect it bt I just dont know how much by.

I was reading up on those kenlowe heaters and theres one bloke worked out using it saves him 2.7mpg during the winter htf did he work that out so precisely :nenau

 

[Kamsin]

The maximum lenth for a Lorry on uk road is 16.5 meters, that is why the bull nose lorry never caught on here. They did have a few running tippers as they can get the weight up to 44 tons.

A UK road train, classed as a wagon and drag is 18.5 meters.

Any how, this was about drag and fuel, YES the roof bars will increase you fuel consumption. I did say i was going to post tips on this but have not had the time to do it yet, as i want to make sure its right.

But here are a few:-

Dont let your car warm up before driving it, modern cars dont need it, just dont thrash it to death before its warm and its fine.

Reverse into your driveway or garage, because the engine is warm it will use less fuel for this manover now than reversing out in the morning when its cold.

Dont drive with your window open if its warm and you have aircon, Yes Aircon uses more fuel when its running than when its not, but having the windows open cause drag and that uses even more fuel.

When in heavy traffic or at traffic lights turn the engine off, BMW have add this to some of their cars as standard, they just cut out when stood, then dip the clutch and they start back up and drive away.

Just a few to be gettin on with, i will do a more detailed one soon.

 

[Deleted account DD]

When in heavy traffic or at traffic lights turn the engine off, BMW have add this to some of their cars as standard, they just cut out when stood, then dip the clutch and they start back up and drive away.

The missus's SEAT Leon does that , its quite spooky at first but it does save a massive amount of fuel :thumb2

And as she refuses to have roof bars fitted ...........................

 

[Adz]

Ya wind-up merchant :augie

Unless ya ars sqeeks while ya walk to your vehicle :augie As soon as you move its causing drag
The more you put on or in its obvious its going to increase drag :augie
But i will stick to my words & say it doesnt make a difference, in the respect of it being noticeable to your fuel bill
If you want fuel efficiently used then get a push bike :lol :thumbs

 

[(RIP) PLANK]

if i fill my tank and get 300 miles fomr it

then pot 33 inch tyres on and still get 300 miles

is it possible the milometer is now out of calibration due to the wheel size change, if the speedo reads diffreent then so will the milage? :augie