Fuel Economy

Hepo replied on 24/04/2023 11:00

Hepo

Posted on 24/04/2023 11:00

Hi all. We all know that our fuel economy is drastically reduced when we are towing our caravan. I have a 20 year old swift, and tow with a 2.0l Astra tdci Sports Tourer, and most of the time get 53-58mpg. When towing I get around 37 on a good run.

But it occurred to me that if I fitted a wide roof box on the Astra (I have now bought a S/H one) will it improve the aerodynamics, and help the air to flow to more easily avoid the relatively flat front of the van. Will try it in two weeks time as we travel to Damage Barton, North Devon.

Any comments?

David.

33 replies

eribaMotters replied on 25/04/2023 12:31

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eribaMotters

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Posted on 25/04/2023 12:31

Isn't it more likely to be the torque making the biggest difference on towing ability.

I've done a quick search and the Navara produced 550N/m opposed to the Discos 380N/m.

Colin

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NutsyH replied on 25/04/2023 15:13

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NutsyH

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Posted on 25/04/2023 10:27 by Hepo

Useful thoughts, thanks to all. Yes I will let you know how the trip goes.

Out of interest, the Astra is a 165bhp 2.0L tdci manual. I'm not what you would call a slow driver, but I drive with fuel economy in mind and generally within the max speed limits. As an example, I regularly drive from North Essex to Bedford to support my single parent son, looking after my grandson etc. I have done the 110 mile journey in under 1hr. Two weeks ago, I decided to easy as I had time and set cruise control at 60mph sometimes 65mph. The run was pretty clear other than speed restriction on a section of the A14. I have a picture (taking when it was safe to do so!) showing 63mpg on the display. A lot of vehicles can give better mpg if driven in the correct engine's power range, particularly when moving from stationary etc.

Anyway, as we know, towing is a different matter. Think my 2 year old Cockapoo will have to pull part of the way! Regards to all.

David.

Posted on 25/04/2023 15:13

"I have done the 110 mile journey in under 1hr"

If that's true, you must have exceeded 120/130 at times. Are you extensively trained in that sort of driving? I am, and I wouldn't dream of doing those speeds on the public road (only in Germany). Not the sort of thing you want to publish on open forums.

"I have a picture (taking when it was safe to do so!) showing 63mpg on the display."

Not only is it NEVER safe to do that, it is also illegal. Unless of course you were stationary, with the engine switched off.

EmilysDad replied on 25/04/2023 19:40

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EmilysDad

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Posted on 25/04/2023 15:13 by NutsyH

"I have done the 110 mile journey in under 1hr"

If that's true, you must have exceeded 120/130 at times. Are you extensively trained in that sort of driving? I am, and I wouldn't dream of doing those speeds on the public road (only in Germany). Not the sort of thing you want to publish on open forums.

"I have a picture (taking when it was safe to do so!) showing 63mpg on the display."

Not only is it NEVER safe to do that, it is also illegal. Unless of course you were stationary, with the engine switched off.

Posted on 25/04/2023 19:40

.... "I have a picture (taking when it was safe to do so!) showing 63mpg on the display."

Not only is it NEVER safe to do that, it is also illegal. Unless of course you were stationary, with the engine switched off.

You're assuming Hepo was using a phone .... cameras will also take pictures 😉 and while it's probably not a good idea to take photos at silly mph, I don't think it's illegal. 🤷‍♂️

Cornersteady replied on 25/04/2023 20:10

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Cornersteady

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Posted on 25/04/2023 20:10

While maybe not illegal to use a camera the Police could still say you were not in full control of your vehicle?

I remember someone getting prosecuted for eating an apple.

Freedom a whitebox replied on 25/04/2023 20:22

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Freedom a whitebox

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Posted on 25/04/2023 20:22

Im wondering if the 1hr is a typo and was meant to be 2hr

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EmilysDad replied on 25/04/2023 21:14

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EmilysDad

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Posted on 25/04/2023 20:10 by Cornersteady

While maybe not illegal to use a camera the Police could still say you were not in full control of your vehicle?

I remember someone getting prosecuted for eating an apple.

Posted on 25/04/2023 21:14

I did say it's probably not a good idea ....

Lutz replied on 26/04/2023 06:24

Lutz

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Posted on 25/04/2023 12:31 by eribaMotters

Isn't it more likely to be the torque making the biggest difference on towing ability.

I've done a quick search and the Navara produced 550N/m opposed to the Discos 380N/m.

Colin

Posted on 26/04/2023 06:24

Torque has absolutely no effect on the stability of an outfit. It’s horsepower that gets you over the hill, not torque. Low speed torque only makes driving a little more relaxed as you don’t have to change gear so often, but it doesn’t affect towing ability.

JohnM20 replied on 27/04/2023 10:50

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JohnM20

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Posted on 24/04/2023 11:15 by EmilysDad

Years back you used to be able to buy an aerofoil/spoiler thing to fit the roof of your tow car that was supposed to improve aerodynamics when towing .... the fact they don't sell them anymore might suggest that they didn't work very well .... though HGVs still have something similar on the roof of the tractor unit 🤷‍♂️

37mpg when towing!? I can't get that solo in my towcar 🙄😉

You'll have to let us know how you got on. 🙂

Posted on 27/04/2023 10:50

When aerofoil spoilers were around I recollect a test being done which showed they saved about £0.50 per 100 miles. It would take a fair time to recoup the cost of the unit so that’s the probable reason for their demise.