Roof boxes - do they alter the towing dynamics

mrp62
mrp62 Forum Participant Posts: 44
edited April 2020 in Towcars & Towing #1

My out fit is a vw tigian and a elldis affinty 554 . Im quite happy with the set up although the tiguan has, in my opinion , steering that is too light.

If i add a 420 litre roof box, to the tiguan,  how will it alter the towing dynamics ?

Comments

  • DavidKlyne
    DavidKlyne Club Member Posts: 13,859 ✭✭✭
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    edited April 2017 #2

    I can't comment on your particular car but for some years I towed with two Kia Sorento's on which I used a roof box on our longer trips to Europe and certainly didn't notice any effect on the driving of the cars. There was a slight advantage (other than providing a lot of extra stowage) in those countries with lower speed limits like Germany and Austria I actually got better economy. However that benefit was soon wiped out at the higher speeds allowed in France.

    David 

  • Lutz
    Lutz Forum Participant Posts: 1,564 ✭✭✭✭
    edited April 2017 #3

    The roof box will undoubtedly have some effect on fuel economy, but it could go either way depending on its shape, size and for/aft location relative to the roof of the car, so it is impossible to pass comment which would in any way tell you very much.

  • ValDa
    ValDa Forum Participant Posts: 3,004
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    edited April 2017 #4

    We find that towing with our Mondeo estate we get slightly more MPG with the top box on, but as soon as we go solo that changes and we get less!  Add to that the technical issues of physical size, and shape as Lutz mentions, means the only way to find out for yourselves is to try it and see.  However, you'll have to make sure you check on the same journey, with the same wind conditions.............. because these will also affect the results!!!

    We now take a top box if we absolutely need to - rather than on every journey as we used to, because there is a problem storing the top box whilst at the caravan so removing it to drive without it whilst on site isn't really an option!

  • mrp62
    mrp62 Forum Participant Posts: 44
    edited April 2017 #5

    Thank you for the replies. It's not so much the mpg that concerns me , but the change in the tiguans  profile would affect the air flow over the caravan.  Would the fitting of a roof box affect the caravan ie would it help to induce snaking 

  • commeyras
    commeyras Club Member Posts: 1,853 ✭✭✭
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    edited April 2017 #6

    Wouldn't have thought so.  If the box is central as it will act as a 'deflector'.  Snaking is as a result of other factors - nose weight, speeding, poor loading, bad match car/caravan etc.   Wouldn't worry about it.

  • Cornersteady
    Cornersteady Club Member Posts: 14,426 ✭✭✭
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    edited April 2017 #7

    As others have said when we had a full complement we towed with a rigid roofbox and there was no apparent change in anything. However I didn't like the fact that when not towing it was empty and the car didn't look as good (vanity). I've now got a semi rigid one which I use when necessary. Its made of fabric but that means its easily fitted in literally minutes and you can take it off when you've arrived on site and its fold away to be stored in your car boot (which does seem strange). Google Thule Ranger 90 or see here for a video:

     https://www.thule.com/en-gb/gb/cargo-carrier/car-top-carrier/thule-ranger-90-_-601100

    There is a cheaper version from a company called Handiholdall which my brother uses and its seems just as good, wished I'd seen it before I got the thule one 

  • Lutz
    Lutz Forum Participant Posts: 1,564 ✭✭✭✭
    edited April 2017 #8

    Caravans, being big boxy things towed at moderate speeds, are relatively unaffected by any form of aerodynamic change, so don't expect any noticeable difference in respect of stability.

  • ValDa
    ValDa Forum Participant Posts: 3,004
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    edited April 2017 #9

    We didn't notice any change at all in the aerodynamics and the caravan towed no differently with or without the roofbox.  It certainly didn't 'induce snaking' with a roofbox on.  The only thing we noticed was that we got less squashed insects on the caravan front window with the roofbox fitted on the car!!!!

    Our caravan has shock absorbers fitted anyway, so is very stable when towing.

  • charlieboy2608
    charlieboy2608 Forum Participant Posts: 25
    edited April 2017 #10

    It would raise your centre of gravity but increase the weight of your vehicle favouring the towing ratio.....position is essential to prevent whistling too!

  • Lutz
    Lutz Forum Participant Posts: 1,564 ✭✭✭✭
    edited April 2017 #11

    It doesn't affect the weight ratio because the weight ratio is based on the kerbweight of the towcar, not its actual weight.

  • charlieboy2608
    charlieboy2608 Forum Participant Posts: 25
    edited May 2017 #12

    Oh dear I knew i'd be entering into the lions den by mentioning the towing ratio somebody would quote the obvious ;-)

    Maths is still maths so by increasing the weight it still changes the ratio!

  • Tinwheeler
    Tinwheeler Forum Participant Posts: 23,138 ✭✭✭
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    edited May 2017 #13

    No it doesn't. It's the kerb weight of your car that matters as stated by the manufacturer. If the kerb weight is 2000kg, it will still be 2000kg even with 6 roof boxes on top. 85% of your kerb weight will always be the same figure.

  • Wildwood
    Wildwood Club Member Posts: 3,581 ✭✭✭✭
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    edited May 2017 #14

    I have to agree that it is not going to change the towing performance. If you have a hatchback or estate and have the box finishing near the back of the car it might improve the airflow and give you a small increase in fuel consumption.

    Probably the most noticeable effect will be keeping dead flies off more of the front of the caravan.l

  • peedee
    peedee Club Member Posts: 9,387 ✭✭✭
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    edited April 2020 #15

    Deleted User by, posted in error

    peedee

  • richardandros
    richardandros Club Member Posts: 2,681 ✭✭✭
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    edited April 2020 #16

    Not quite the same set up as you are talking about, but I tow a Knaus Starclass with a Touareg which has a spare wheel mounted on a roof rack.  Anything less aerodynamic, I can't imagine! It makes no difference whatsoever, other than for a slight increase in fuel consumption.

  • marchie1053
    marchie1053 Forum Participant Posts: 584
    edited April 2020 #17

    I can be less aerodynamic than you! We tow a Swift Charisma 230 with a VW Tiguan and stopped at our French Hovel on the way to Spain in December just past to stick 2 bikes up on the roof bars of the car. Reduced the braking effort on the descents in the Pyrenees and probably added 5%-7% to the diesel consumption. Glad to be able to drop the bikes off in France on the return leg because we drove from Newhaven to Scotland on the day of the violent winds, 24th February! Turning onto the A27 dual carriageway from the Newhaven exit and struggling to reach 40mph as the headwind encountered Swifty was not very pleasant!

    Steve

  • derekcyril
    derekcyril Forum Participant Posts: 408
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    edited April 2020 #18

    Remember those wind deflectors from the 60s ,what happened to them ?

  • ABM
    ABM Forum Participant Posts: 14,578
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    edited April 2020 #19

    Melted down, recycled into Top of the Range Caravans I suppose  wink

  • DaveT
    DaveT Forum Participant Posts: 174
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    edited May 2020 #20

    Windslammer I think was a brand name. Good in theory but something else to add to the caravan list and not everyone had access to wind tunnel to optimise the flowsmile.

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