Rangie Fuel Consumption; Roof Rack vs Trailer.......

[Bluey]

Hello everyone,

I am after your opinions/proven figures on the difference in fuel consumption of a Rangie 4.6 HSE with the family onboard, the cargo area loaded with gear and a roof rack sensibly loaded and covered with something like a Michelle's Sac's or similar item to reduce drag, versus the same load of people in the vehicle but no roof rack this time and all the gear in a trailer. (same rims and tyres as the tow vehicle.)

i.e.

Rolling drag and the extra weight of the trailer being towed

versus

Drag from the roof rack and items loaded on it.

All this assumes the same items being loaded in each case.



Interested in your thoughts.

Regards,

Bluey.

[LavisLane]

Hmm, bit of a head scratcher;

- Roof rack will create drag
- Trailer will add load in the added weight of the trailer itself

You need a formula that states a measurement of drag in kilogram weight. Guessing that you can then multiply that by the hours your driving.

My guess is this;

Short trips - minimal drag, go the roof racks
Long trips, lots of drag potential at prolonged higher speeds - go the trailer

:BigThumb:

[Camo]

My dads P38 does flat 14l per 100k on the highway and 16 flat when pulling an 800kg camper trailer.

That was the average on a 5000k trip

Camo

[JDNSW]

I think the answer is "it will depend" - on how you drive, mainly.

If we analyse it:-

Both will increase the fuel consumption, but the mechanism of that increase is different.

The roof rack will increase it by the increased aerodynamic drag, both from disruption to the airflow and from the increased frontal area. This increase in drag is proportional to the square of the speed.


The trailer (depending on its actual design) probably does not increase the frontal area, and may well have little disruptive effect on the airflow, and conceivably could even improve it. To a large extent it will be in the "dead" air behind the car. However, it almost certainly adds significant mass compared to the mass of the roof rack, and has additional rolling resistance from the extra two tyres. The extra mass uses extra fuel only when accelerating, and the rolling resistance is proportional to speed.

This analysis suggests that the roofrack would be preferred if travelling slowly or doing a lot of stop/start or hilly driving, but the trailer for sustained high speeds on level ground.

John

[Rangier Rover]

My 89 Rangie is much worse on fuel Towing than with a rack up top.

[Bluey]

Thanks for your Input guys. I am leaning toward the roof rack I think at this stage so will start a new thread to find a picture of one on my model.

Kind Regards,

Bluey

[Diego Luego]

I found with my TD5 Defender that the genuine Landrover roof-rack caused
exactly the same fuel consumption drop as my camping trailer -2 to 3 L/100k.

In other words you may as well take the trailer.

[PhilipA]

IMHO the aerodynamic effect increases greatly over about 100Kmh.
The effect of a 30-40Kmh headwind on my RRC in the last two weeks was profound.
So if you normally travel at 100Kmh plus, the trailer would be better.
I have been getting around 16L per 100km at 105 on cruise on flat country with my 92 RRC with many engine mods, towing my 650-700Kg camper.
If there is a headwind the consumption goes up to 17-18 maintaining a similar throttle position which slows the car to say 90Kmh.
Regards Philip A

[Hoges]

The best way to get some sense of the impact of roofrack vs trailer is to do a trial using a relatively modern sedan or wagon with both an an instant and average fuel consumption readout on the trip meter. Then do a series of runs over a known route with an observer recording specific and average consumption for given speeds ...unloaded vehicle/roof rack/trailer etc.

The differences are very interresting and will generally confirm to the "rules of thumb" outlined previously....trailers for sustained high speed, roof rack for "meandering" journeys...in both cases fuel figures increase significantly above 90-100kmh due to aerodynamic drag, especially the roof rack

The problem with a trailer is the temptation to take too much stuff...

If it comes to bulky/lightweight kids' stuff...bikes/trikes/etc etc a trailer is probably best...easier to load /less likely to damage the roof of the P38, gentler on the back muscles...and provided you drive /accelerate smoothly it will get its own momentum up and tend to "roll along" at 80-90 kmh.

A trailer covered with a tarp properly held in place with an elastic net over the top is best i.e. no billowing = less turbulence = less drag...

[spdterence]

I think 4WD Action magazine did this very thing a few months ago. They measured about 3 different vehicles, Cruiser 100, Pootrol and something else and they all returned worse fuel consumption towing a trailer than with a roof rack.
I don't think the Brand of 4x4 up front really will alter this equation much.
A trailer has at least 4 ft x 18in of frontal area plus 2 x tyres drag - the roof rack much less frontal area I would guess.

If I think back on the wind tunnel tests etc that I have seen on TV plus riding in a convertible. I was quite surprised in the convertible that you could hold your arms up directly above your head and there was very little wind velocity there - but if I really stretched up, then it would get pretty fast. I think the wind pressure from the bonnet and windscreen has already been pushed up and over the top.
I am wondering now that I have said that what the ideal position for the front of the roof rack ( forward and aft) might be?
Perhaps about 12-18 inches from the top of the A -Pillar - Just a gut feel on that though.

Terry

[trobbo]

I think 4WD Action magazine did this very thing a few months ago.
Terry

I was going to mention that article myself... and as I turn around there's the mag edition 123 setpember 2008.

Using what I thought were less than technical comparisons they took an 80 series petrol and a GQ diesel patrol and drove 300 km around the 'block'. They compared fuel usage with a trailer and roof top tent. The patrol used 27% more fuel towing and the 80 series used 22% more fuel.

(BTW I dont normally buy it anymore but the article caught my attention).

[Utemad]

I think that fuel use aside, unless you have both and are wondering which you should take on a particular trip, then it depends on what you want to carry.

If you only have a little bit of stuff then put it on the roof but if you have a heap of stuff or heavy stuff then put it in a trailer.

Also it is much easier to store a roofrack when not in use than it is to store a trailer. Plus a roofrack has nearly zero maintenance.

[drivesafe]

IMHO the aerodynamic effect increases greatly over about 100Kmh.
The effect of a 30-40Kmh headwind on my RRC in the last two weeks was profound.
So if you normally travel at 100Kmh plus, the trailer would be better.
I have been getting around 16L per 100km at 105 on cruise on flat country with my 92 RRC with many engine mods, towing my 650-700Kg camper.
If there is a headwind the consumption goes up to 17-18 maintaining a similar throttle position which slows the car to say 90Kmh.
Regards Philip A

I have towed heaps of trailers and most of the time on long trips.

I have never owed or used or intend to use roof rack for safety reasons, mainly because of the way I drive.

I regularly drive at night with 4 roof mounted driving lights and I’ve found, as Philip posted, travelling at speeds over 100 kph knocks hell out of the fuel consumption, even with the TDV8.

A trailer on the over hand, causes more fuel to be used will accelerating but once you are up to your cruising speed, accounts for very little additional consumption.

So if you are going to be lots of stop start running, which means low speeds, a roof rack would be the way to go.

If on the other had you see much of your trip being out cruising on the open road, for my money, particularly as you carry heaps more in a trailer than you could ever do with roof racks and where it’s convenient, you can leave the trailer while you do some local exploring. Bit harder to take the roof rack off.

One more point, I have never heard of anyone having problems parking in an undercover parking location while towing a trailer.

Don’t forget to duck if you try to use an undercover car park with roof racks on.

[cartm58]

Without knowing what your intending to be doing or going l think your making the wronf decision, it should be what l can fit on a roof rack compared to a trailer and the trailer will always win out.

Go the trailer unless your heading on a trip across the Simpson

[drivesafe]

Just a suggestion, but hows about someone setting up a poll.

I’d do it but I don’t know how so I’d rather leave it to someone who knows how. ( It’s called passing the buck ) :twisted:

Cheers.

[edddo]

I have done extended touring trips with both set ups in my tdi...my results are very clear, towing a moderately loaded trailer increases fuel consumption by approximately 10% over the loaded roofrack or roof top tent. Econ figures are 11 l/100km for rooftop and 12 to 12.5 for trailer(approx 800gross)...And with this I would say that my average touring speed was 5 to 10 km/h faster with the roofracks/rooftop so a figure of 15% is probably closer to the mark for a similar highway touring speed.. I know in theory that the trailer may not add to wind drag but lets face it the dead weight of the trailer is a factor in all driving conditions...accelarating and cruising. To say otherwise ignores the laws of physics..if you disagree with this you are saying that a particular vehicle weighing 2 tonnes will have exactly the same performance characteristics of as if it somehow only weighed one tonne.....
As others have said, I would expect this differential to increase if driving was more stop start or slow as the wind drag from the roofrack would decrease with speed.

[PhilipA]

Of course there are roofracks and roofracks.
If I were to use my roofrack , I would get one of those streamlined coffins, and make sure the bars were as near to the car as possible.

And I have to agree that in general a roofrack is better, but it is hardly an argument, because if you need a trailer you need a trailer.

In my case I have a Campomatc hard floor camper trailer which has a heavy duty tent with about 2.5 metres head room , queen bed with 4 inch foam matress plus 1 inch cellular foam, lino floor, Kitchen, and about 12-15 Cubic metres of storage plus 2 jerry cans , gas bottle, and toolbox on the front, Oh and 60 litres of plumbed water, and a spare tyre, and 240 volt and 12 volt leads , plugs etc. Try that on a roofrack.
Regards Philip A

[drivesafe]

queen bed with 4 inch foam matress plus 1 inch cellular foam, lino floor, Kitchen, and about 12-15 Cubic metres of storage plus 2 jerry cans , gas bottle, and toolbox on the front, Oh and 60 litres of plumbed water, and a spare tyre, and 240 volt and 12 volt leads , plugs etc. Try that on a roofrack.
Regards Philip A

Try putting all that on a roof rack ( AND being able to stay upright too ) :angel:

[pop058]

Another minor detail not related to actual fuel consumtion is the quantity (as previously stated) and ease of placing and recovering your loaded gear. much easier from a trailer, kids can even do it. I dont think I would like to see little people pack thier BMX (for example) up on the roof of my P&J (pride & joy)

[slug_burner]

It comes down to a load capacity issue. Check your handbook and see what the maximum roof load is. You will find it is not that much.

I used roof bars for a trip to the Kimberley and then back across the Simpson. I was glad not to be towing a trailer especially for the small amount I had on the roof bars. But there is a limit as to how much you can put up there and if I had of exceeded that limit then it would have been a trailer and you would put up with whatever inconvenience and fuel consumtion hits people have talked about previously.

At home; if you have the space to keep a trailer it is much more convenient than roof bars or roofracks. To put a trailer on it is two minutes if your slow. Any fuel saving to be had by the roofrack will be lost as you drive around everyday with the rack on top as it is a pain to put them on and off, bars a little less of a pain but still takes longer than putting the trailer on the back. If I am going to pick up building material or take something down to the tip I will put on the trailer in preference to any roof mounted device.

[rofosixone]

hired shippshape car top tent up hornsby way nsw for 3 week trip around tas to put on my p38a .found used extra 0.6 L per 100 km ,dont realy notice it driveing but do hear wind noise faster you go .towing the cub camper trailer used av extra 1.3L per 100km dont notice it because have v8 grunt but off road more so reversing is when you notice it then .rather pay extra in fuel than $60/$100 nite ,pays for it self long run.