Twin rear wheel chassis - pros & cons?

Discussion in 'Tech/Mech General' started by Dafydd, Dec 31, 2014.

  1. Dafydd

    Dafydd Funster

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    Of the vans I'm looking at for a 2015 purchase one is on a MB516 with twin rear wheels - the equivalent of the Fiat tag-axle for a GVW of 5 tonnes.
    (I'm looking for a MH with a large payload over the standard MIRO for long-term touring).

    Besides the extra tyre costs (I assume) involved with having 6 wheels what other things should I be considering from the point of view of day-to-day driving and maintenance?
    Increased fuel consumption? Difficulties with checking/topping up tyre pressures? Can snow chains be used?

    The space, storage and payload are the advantages of a 5t (7.6m) van but what are the downsides/extra considerations that I need to be aware of given the extra set of wheels necessary for the weight?

    Any thoughts appreciated.
     
  2. BreweryDave

    BreweryDave Funster Life Member

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    My thoughts (having a Fiat tag) are that if you need the advantage of the extra payload, then you have no choice.
    Therefore the only downsides are - you can't have a smaller motorhome.

    A tag is very stable, you are looking at the merc with twin wheels on the same axle, which I had on an RV. No real difference - as it's on a twin axle instead of a triple axle - to give you the load carrying capacity.

    Obviously - tyre wear will mean 6 tyres instead of 4, and the increased weight of a 5 T van over a 3 T van will mean its greater - but if what you want and need is a large payload - then these things are irrelevant.
     
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  3. Larrynwin

    Larrynwin Funster

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    The other advantage of the twin rears on single axle is it will be rear wheel drive and as a result much better traction on wet grass, snow etc as most of your weight is over the drive wheels .
     
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  4. hdvrod

    hdvrod Read Only Funster

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    On twin wheels you have a valve extension to check the inner tyres.
     
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  5. funflair

    funflair Funster Life Member

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    Deffo better traction with 4 wheels on the one rear axle especially if you get it with diff lock, fair chance your tyres will be old before they are worn out but will wear better on the single axle variant as not scrubbing when dragging the tag axles around corners.

    Getting at the tyre valves is no problem as you can run a pipe from the inside wheel to wherever you want it.

    Don't know about snow chains but I would guess just fit to the outside two wheels
     
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  6. Larrynwin

    Larrynwin Funster

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    Yes I have snow chains for mine but never needed them in anger image.jpg
     
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  7. Jean-luc

    Jean-luc Funster

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    A friend of mine with a Hymer on a Merc twin wheel chassis ended up on a Aire on which fell a few inches of snow overnight. After breakfast he just set off using the diff-lock and passed half a dozen others unable to negotiate the uphill exit. He has also towed vehicles off rally fields.

    From a traction point of view a rear drive twin wheel set-up with diff-lock is far far superior than front wheel drive.
     
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  8. funflair

    funflair Funster Life Member

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    Is that just the two outside wheels ?.
     
  9. JeanLuc

    JeanLuc Funster

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    Another, perhaps minor, advantage of the twin rear wheels over twin rear axles set-up relates to touring in France. It has been reported that some French campsites will not allow twin axled caravans or motorhomes; it's a way of banning travellers (gens de passage) who often use twin axle vans, without appearing to discriminate against a specific group.
    This may not be a big issue for you but as an example, here is an extract from the site details for Amboise municipal site in the Loire valley.
    Spanning an area of 3 hectares, the local campsite of Amboise, rated 2 stars, has 300 sites, mostly shaded and very spacious to accommodate tents, caravans and motorhomes (with the exception of double axles).
     
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  10. Larrynwin

    Larrynwin Funster

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    Yes it would be near impossible to get them on the inner ones.
     
  11. pappajohn

    pappajohn Funster Life Member

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    Tolls, both here and abroad, could be higher.
     
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  12. StefAndDi

    StefAndDi

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    I'm really pleased to read your post as my new MH will be a Hymer with Mercedes twin-wheel rear axle.

    Stef.
     
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  13. ASel

    ASel Read Only Funster

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    A TAG axle MH will be class 4 for tolls in most European countries but twin wheel back axle MH will only be class 3. See here http://www.autoroutes.fr/fr/classification-des-vehicules.htm

    We had a 4.5T TAG axle Fiat and the traction was so poor that on one occasion we could not set off at a junction as the gradient was too steep and the wheels just spun, this was on a dry road.
     
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  14. Dafydd

    Dafydd Funster

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    Thanks for all the replies, very reassuring. Rear wheel drive is one of the reasons I'm leaning towards MB.

    Three years ago (when my MH research started) I was looking at panel van conversions, then semi-integrated and now I'm settling on a 5t monster (and a bill to match)!

    Thanks too to @Judgemental who made me seriously consider payload for long-term touring - you were right, the La Strada is far too limited. When I add up the weight of optional kit, my stuff, companion & their stuff, food, booze and kitchen stuff, birdwatching stuff, camping furniture, bicycles, winter stuff ... it's several hundred kilos so I'm only looking at (A class) with >800kg above the MIRO.
     
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  15. funflair

    funflair Funster Life Member

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    I reckon the IVECO is a pretty good chassis and certainly good for weight as they can go up to at least 7.2t, if you are buying new you can now get the ZF torque converter auto which has to be an improvement over the older Agile robotic auto. I think more converters are using the IVECO than the Merc.
     
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  16. trekkin

    trekkin Read Only Funster

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    A lot easier to level a twin wheel axle using chocks or ramps, have seen some scary sites where owners have only used one ramp on a tag axle, one wheel on the ramp one on the ground, just looks wrong.

    Tags are more stable on the road but often front wheel drive, on the soft grass one wheel follows in the rut of the other whereas a twin wheel spreads the load across the van and as said better traction from rear driven

    Horse for courses, but seems you have got your requirements sorted so the rest will follow.
     
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  17. DavidG58

    DavidG58 Funster

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    Is the diff lock an option? is it likely to be something I have and don't know about? sounds very useful

    To OP, I have a twin wheeled rear axle, gives us a long over hang on an 8m MH but had no issues at all with traction in 2 years, valves have extensions on for checking / filling
     
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  18. funflair

    funflair Funster Life Member

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    Hi David

    I think you will have what they call ABD auto braking differential which uses the braking system/ABS sensors to brake a wheel that starts to spin thereby putting the drive to the other wheel. The good news is that it does this by itself so you don't need to look for any switches.

    Now you just need to go find some snow and see if it works.
     
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  19. JeanLuc

    JeanLuc Funster

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    My Hymer is on an older Sprinter than yours David (2003 316 5-speed auto). It has an ESP programme that does what 'funflair' is referring to. Yours may be more sophisticated than mine but it may have limitations. It is a great safety tool under normal circumstances; e.g. it will correct minor wheelspins in snow. However, it is not as useful as a proper diff-lock or limited slip diff in the real goo. (My all-wheel drive Subaru Outback has the latter and the traction is amazing.) If the motorhome is stuck in really slippery mud (has only happened once) the ESP first slows down the slipping wheel, then the other one as that starts to spin. Power to the spinning wheels is reduced progressively to the point where the engine virtually shuts down. At that point the only option is to get out the folding shovel and dig, and/or let down the tyres significantly.
     
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  20. flatpackchicken

    flatpackchicken Funster Life Member

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    Rear wheel drive with a twin tyre each side axle seems to be the best set up that you can get,, as a lot of weight goes over the back axle especially when you have quite a big overhang such as mine on an 8.2m mh, and I put it to the test this winter coming through France about 50km before I got to the Millau bridge:france:, as I was about 1200 mtrs up on motorway and had snowed about 6" and police was dealing with a small accident van and car, so I had to stop as was right in front of me, and French mh pulled up alongside of me (normal fwd Peugeot) and when we could go the French man could not get going again and the police were trying to get him into the side, maybe to check if he had snow chains, but I with my finger poised on the diff lock button just pulled away and did not need the diff lock (result although as virgin snow by this time), and did not need my snow chains either, double result,,,, although if it had not started to clear as I started to descend I would have put my snow chains on for safety , overall very impressed with RWD (rear wheel drive) and have had no problems anywhere so far in getting of wet grass or slippery inclines, (although I am ready to pull Sundowners:notworthy2: out now always will be grateful for there Beast:notworthy2::notworthy2::notworthy2::notworthy2:) all in all would never have a FWD again if I had a choice.
    Regards Garry Flatpackchicken
     
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