Fuel Economy
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.
Comments
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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. 🙂
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North Devon and the Westcountry in general are probably the worst areas for fuel economy so don’t expect miracles. Go to Norfolk instead😀
Like ED, I consider 37mpg towing to be brilliant. Our Shogun gave 16 towing and about 28 solo.
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With our Sorrento it's about 25 to 29 mpg towing.
(Of course to make it a fair test you'll have to have the roof box empty)
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At 37mpg you are doing well. I expect a minimum 34/36 mpg but on a good long motorway run return 40mpg. I averaged this figure in Holland last summer and then when towing from Merseyside to mid Devon when we moved down last Sept. I have a 1.5 petrol Audi manual but tow a wind defeating pop top Eriba at 1200kg.
Colin
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Caravans are about as aerodynamically imperfect as you can get. They don't lend themselves to much improvement whatever you do to them or to the towing vehicle so don't expect miracles. The overall frontal area of your outfit doesn't change one bit if you have a roof box or not.
Caravans and good aerodynamic performance simply don't mix very well. As the aerodynamic drag increases with the square of the speed one might get some improvement on a long and relatively fast run, but nothing in slow heavy traffic.
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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.
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110 miles in less than an hour! That’s not something I would be proud of🤨
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As we all know we cannot beat the laws of physics, but we can also use them. If you look at the power output specification of most cars you will note peak torque is usually around 1,900rpm. At this point the engine is working at it's most efficient and also happily for us when we have a van on the back is at the sweet point for if we need it. If you drive at these revs I strongly expect you will see 55mph on your speedo.
Colin
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There is no substitute for horsepower and design for intended use. My Navara 3L V6 would return around 30mpg when towing my Valencia. Set the cruise control and it wouldn’t deviate from the set speed. It’s replacement discover sport 2L has been returning 24- 28 mpg towing the same caravan and you have to override the throttle on hills or it loses speed. - that said, solo and around town, the discovery is a lot sweeter on the wallet
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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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"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.
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.... "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. 🤷♂️
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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.
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Im wondering if the 1hr is a typo and was meant to be 2hr
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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.
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110 mph! Here in North Devon you're lucky nowadays to get above 30 and even luckier if you can stay on the right side of the road with all the potholes that are now dangerous craters. This afternoon on the way back from Tescos I stopped to help a driver change a wheel that was destroyed by a crater. Makes it all the more scary when it's raining when the road looks like puddles.
Back to mpg, I've had my van for 9 1/2 years and never once worked out the mpg. Gauge gets to quarter, fill it up.
JK
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Actually I meant to ask. Re. my trip to Damage Barton, North Devon next Saturday (Coronation Day!!). I'm thinking the best route from any point on the M5 is to leave at the Tiverton junction (27) and use the A361? It seems the easier route for caravans. Any advice gratefully received.
David.
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Definitely J27 Hepo. Stay on A361 all the way, past Barnstaple and follow signs to Ilfracombe. At Mullacott cross roundabout take the 1st exit for Woolacombe / Mortehoe. Go past Bay View campsite, around a sharp right hander (Turnpike Corner) then in about 200 meters on left hand bend turn right. Follow for 5 minutes, DB is the second campsite on the right. Plenty of space to choose from , there was only 25 vans there yesterday
JK
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In answer to the point re roof boxes, I have some experience of this. When we had a caravan, towed by a Kia Sorento auto, we used a roof box on our long overseas trips. What I found was that whilst towing in Germany, with a lowish max towing speed on the autobahns I did see a modest improvement in fuel economy but as soon as we were in France with a much higher towing speed limit any previous advantage was lost. So it seems that if you tow at modest speeds you may get a slight improvement but as the speed increases the advantage is lost. Don't forget that unless you remove the roof box when you get to your destination that will make the general economy worse if you leave the box in place. The only reason to have a roof box is really as extra storage rather than hoping for any improvement is towing economy.
David
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How many miles will you need to travel at improved economy to pay for the roof box with the savings….. 50,000? Going from 23mpg to 25mpg or whatever is neither here nor there. If economy is such a financial issue then perhaps caravanning is not affordable for you given the other costs involved?
However I am not sure what towing speed limits in Germany and France you are referring to DavidK?
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In Germany the limit is 80 kms per hour (unless you had the Tempo 100 sticker) and in France (when we last went) 130 kms per hour so quite a difference and no I didn't tow at 130 kms per hour!! The fact I had a roof box was just incidental to the economy achieved, it was just something I noticed over many hundreds of miles of motorway towing in both countries. I had a roof box because I wanted out of the way storage whilst we were on route to our destination. Totally agree that it would be a waste of money buying a roof box to achieve extra economy but the OP did ask.
David
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Totally off topic and apologies but when we had our second motorhome it had a large roofbox on it at the rear bolted to roofbars with a 150mm gap to the roof. Back then I was minding the budget and I found there was a difference of 8 mpg when I took the box off. That's a big chunk of gas when I only used to get 24mpg.
JK
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