Do roof and fuel economy

Hi Guys,
Can anyone give me some idea of how much roof racks will effect fuel economy.
I run an 80 series petrol on LPG so fuel costs are ok at the moment.

I just wonder how an extra 20cm of height and 20 kg in weight will effect the economy.

The problem is that I keep finding things to take camping and need to put a couple of things on the roof rack.

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Reply By: Outbacktourer - Tuesday, Apr 27, 2010 at 09:20

Tuesday, Apr 27, 2010 at 09:20
Based on my experience it won't do you any favours, probably 4L/100Km in petrol at 100KPH, what that does to gas I don't know?

AnswerID: 414428

Reply By: Member - Roachie (SA) - Tuesday, Apr 27, 2010 at 09:23

Tuesday, Apr 27, 2010 at 09:23
When I had my GQ Patrol (diesel), it made a difference of about 10%. I could do 1100klm on a tank without the rack, but only 1000klm with the rack fitted.
AnswerID: 414429

Reply By: Member - Robbie Reddog (WA) - Tuesday, Apr 27, 2010 at 09:57

Tuesday, Apr 27, 2010 at 09:57
I had a full length rack on the 100 series diesel and had it off the car for the last couple of months. Difference is about 1lit per 100kms.
AnswerID: 414434

Reply By: Ozhumvee - Tuesday, Apr 27, 2010 at 09:57

Tuesday, Apr 27, 2010 at 09:57
On our troopies the roofrack (approx 250mm high with rack bag) and on the rear flat section of roof caused approx 10% increase in fuel consumption.
Towing the hardfloor camper trailer (which weighs around 500kg loaded) caused the same increase in fuel consumption.
On the Humvee neither make much difference at all.
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AnswerID: 414435

Reply By: Alloy c/t - Tuesday, Apr 27, 2010 at 10:01

Tuesday, Apr 27, 2010 at 10:01
Had / put an Opposite Lock 6 leg ally roof rack on our 80series turbo diesel auto , made no difference to fuel consumption around town [Brisbane]
H/way use another story , average of 1klm less per lt and that with r/rack empty ,
Modified r/rack to carry our 12ft tinny ,
Tinny on top and some other gear in rack lost another 1klm per lt ,
All up height with tinny on top became 2.87mtr so had to uput warning label on speedo to "remind" of height , [ underground car parks even without the boat on the rack became a no go zone].
AnswerID: 414437

Reply By: Member - joc45 (WA) - Tuesday, Apr 27, 2010 at 12:03

Tuesday, Apr 27, 2010 at 12:03
I've got a 3/4 length steel RR on my GU diesel with solar panels on top. Makes about 1L/100k difference. But also the load in the vehicle seems to make a similar difference; ie, loading the interior up heavily alone increases the consumption on the highway.
I made a very neat deflector for the front of the RR (quite proud of it!) but it made bu99er-all difference to the consumption.
If I'm in no hurry, I now sit on about 90km/h instead of 100-110, and it makes quite a difference to the economy.
AnswerID: 414447

Reply By: Member - Doug T (NT) - Tuesday, Apr 27, 2010 at 12:15

Tuesday, Apr 27, 2010 at 12:15
I don't know about your roof racks but I do know that having an Oversize sign up on my Troopy with a full fuel load of 360Lts running Brisbane Port to Mt Isa , 1,846Klm I could just get by with a little left, I towed my 20ft caravan from Southern Cross to Pt Augusta 2,020 Klms and still had some left , so I see the the difference of having something high on the roof.

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AnswerID: 414449

Reply By: Member - Geoff H (QLD) - Tuesday, Apr 27, 2010 at 15:40

Tuesday, Apr 27, 2010 at 15:40
Thanks for the help guys,
Is there any benefit in locating the roof rack further back on the vehicle to sit in behind the wind deflection of the windscreen.
AnswerID: 414465

Follow Up By: Member - mazcan - Tuesday, Apr 27, 2010 at 18:32

Tuesday, Apr 27, 2010 at 18:32
there is some merrit in that thought as far as wind deflection goes but

if you put it too far back you will have too much weight on the rear axle
and could cause a steering or stability problem?????
FollowupID: 684692

Reply By: trainslux - Wednesday, Apr 28, 2010 at 10:48

Wednesday, Apr 28, 2010 at 10:48
I put highmount roof racks (thanks Porl), and then a rola roof basket,and side awning, and found no difference in fuel economy in our hilux 2.8 diesel.
We normally cruise at 90km/hr.
Was quite surprised, especially after battling head winds to Broken hill, only to find fuel burn was 10.5lts/100km with pram on the roof basket.

AnswerID: 414567

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