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Thread: Why do so many European semi's have tandem axle but are single drive!!!???????

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    Why do so many European semi's have tandem axle but are single drive!!!???????

    Always wondered, see many pictures of Euro semis, even heavy haulers like low loaders and similar, and most have a lazy axle.
    Here in Australia most heavy haulers are tandem rear/tandem drive. Hope someone can answer my question as it has always made me wonder why they do this. Tandem drive is superior in muddy conditions, and so on.
    Any answers would be appreciated!! Thanks. Steve.

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    Might have something to do with turning. Being able to lift your tag to make a hard turn in tight city driving would be nice.

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    I have read that single axle tractors w/ locking differentials have superior traction to a live tandem, now personally I'd have to see it to believe it, but they claim to have done testing.

    I can tell you for sure that a single drive axle tractor gets better fuel economy than a tandem.
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    Most interesting info, here in Aussie, just about all tippers, cement mixers are tandem drive, with lockable diffs, so basically if starting to slip/become bogged, driver simply locks the diffs up, drives forward until clear, unlocks diffs and drives away, as i understand it, Basically gives them maximum 4 x 4 traction. only in straight line tho, corner with diffs locked would cause major major damage!!!

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    Super Moderator willie59's Avatar
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    Same thing here steve. Most tandem trucks have the rear tandem live, front tandem is selected for slippery conditions. Don't know why Euro trucks only use single live axle with load carrying dummy, but suspect related to fuel savings as a dummy axle will still have less friction (internal components) than a front tandem that's not engaged. Just a guess.
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    As far as I know, our tandems are all drive full time, im not aware of any that can switch to a single drive from being tandem drive. Seems ours are permanent tandem drive both axles!

  7. #7
    Senior Member joispoi's Avatar
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    It's to meet the per axle weight limits that are on some of the paved roads where traction is not an issue.
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    Very few earth roads in Europe nowadays. Low loaders will go off-road to unload plant, but that's all. Heavier machine movers do favour tandem drive, but as said, fuel consumption is heavier. A lot of the second axles are not just liftable, they steer as well, and save on the tyre scrub. You should see how twisty a lot of roads are in europe generally, UK in particular. In the UK virtually all 6 and 8 wheel tippers have tandem drive as they're off road a lot more.

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    This tandem drive thing it best Euro/U.K. verbs, a tandem drive is called a "Double Drive" this is fitted near always to 3 and 4 axle tippers (dump trucks) and cement mixer spec trucks, on tractor trailer outfits it is standard to see (common) 5 and 6 axle outfits, this is 3 axles under the trailer, with 2 or 3 axles under the tractor, the usual set up is twin steer axles with the rear most axle driving, the mid axle will also lift so when empty its not wasting rubber and fuel, its also 2 spare wheels if you need them, the rear tag axle is not as common as it was 15 years ago, on low loader work double drive is the prefered set up depending on the work style of the company, it is common to see a 6 axle outfit when empty to have 2 axles lifted leaving 4 axles only to wear out the tyres, most tractor units fit big super single style wheels to the front steer axle, as they run cooler and have a good effect to the steering, there is 16.5 ton (16500 kgs) axle loading allowed in the U.K. and Europe under set conditions, near all bridges in Europe are built only giving 4 metre hight clearance, anything over 4.080mm will be a bridge strike, so you need to know your hight??, so the reason that double drive is not on every 3 axle truck is, if its not needed why have it, plus why drag around loads of weight for nothing, near all International running trucks carry snow chains by law.

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    I'm more familiar with Italy and it's all about fuel I believe. A few years ago the only tandem drives that were common were concrete mixers. An uncle there use to run straight dump trucks. Had two front steer axles a heavy drive axle and a rear steer. The rear steer could be picked up when empty or to reverse. If they had to back up with a heavy load there was an air lockup device to keep the rear straight when backing.

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    Being able to lift an axle also helps in the wintertime, when you put 20tons on the driving axle you'll get a good deal of extra traction......ask any trucker running the scandinavian roads in the winter.

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    Senior Member Nige's Avatar
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    Yup, axle loading is the key. You can haul 44 metric tonnes gross weight all over Europe on 6 axles (3 axle tractor + 3 axle trailer) but only 38 tonnes on a 5 axle setup (3 axle tractor + 2 axle trailer or 2 axle tractor + 3 axle trailer). Therefore most haulage companies run 6 axles to take advantage of the additional load carrying capacity. There's no need for the front axle of the tandem to be a driving axle, usually in fact it's a 2nd steering axle in order to improve turning circle. Also it generally lifts up when running empty to reduce drag and improve braking efficiency on the tractor. Usually the air bags to lift the axle are set to a certain pressure and when the load increases the axle drops automatically.

    Vehicles like a 3-axle rear dump truck will always have full time drive to both axles of the rear tandem, due to their need to go off-highway a fair bit. Same with things like concrete mixer trucks and lowboys used for moving heavy equipment.
    I'd love to see things from your perspective but unfortunately....... I find it impossible to get my head that far up my a$$.

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    Thanks all for the helpful answers, Here in Australia, mostly see 3 axle semi, 3 axle trailer, or 3 and 2axle trailer, then we have the B Doubles (B trains) usually a 3 axle semi, then mostly a 3axletrailer with 5th wheel with mostly a 3 axle traile (sometimes only two) B doubles are restricted to main roads usually. It is unusual to see a lazy axle tandem drive semi here, quite a few large delivery trucks have lazy axle though, great on mostly flat roads, nut when reversing up a fairly steep driveway, the rear axle (lazy) took most of the weight, so of course the inner drive axle was almost off the ground, spinning, bogged on bitumen!!! after a couple of attempts he let it roll forward, into reverse, and got a run up, once both axles levelled out it was fine!
    Ive also seen them bogged on building sites with lazy axle taking a share of weight and drive axle only effectively 50% of the ideal traction needed. All the mixers, tippers abd such are all tandem drive!! what is rare here are tri axle rear end on semi or tipper, only see tri drive stuff mainly in the mining areas, outback Australia, Very rare sight around the city area.

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