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

[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