Article for Alex

[Surfer]

Why don't PCV do a review on whether a motor mover on a twin axle should be fitted in front of the axle or whether it should be fitted on the rear.

In front it may increase your noseweight as a twin axle motor mover weighs in the vicinity of 40 kgs and this is difficult ot overcome because if you start moving stuff to the rear you can end up with a tail wag. Also as the front of the towing vehicle is lifted it may cause problems when overtaking trucks. At the rear it may reduce your noseweight too much but this can be overcome easier than the opposite way around.

At present all we have in the front is the gas bottles, 2 x empty aquarolls and the empty waste water drum and my noseweight on my Lunar is quite a bit over the top. Not sure if the 110 amp battery weight comes into effect as it is vitually right in front of the front wheels of the van.

Surely manufacturers should realise that there is a possibility of motor movers and larger batteries been fitted to bigger vans thus having a considerable impact on their weight distribution? Can PCV take this up or do PCV prefer to take neutral stance and not do an investigative journalism in case they offend one of their advertisers?

 

[Lutz]

While on the subject of motor mover weights, I spoke to a representative of the caravan industry (I shalln't say which) why motor movers aren't made available as a factory-fitted option and the answer I was given was that the darned things are so heavy that they would increase the MIRO, and consequently reduce the available payload, to such an extent that nobody would buy the caravan when they read the weight figures published in the sales brochures. When I put it to him that many owners fit them as aftermarket units and are then faced with the same situation, he said that's their problem. Makes one think.

 

[Chris4]

I have a twin with a motor mover fitted to the front wheels. I hae no problems at all. The van tows like a dream and no nose weight problems. I'm no expert but I've read that some vans are excessively heavy at the front. Obviously, the mover would then add to the problem

 

[parker1158]

Hi All

I would imagine vans are much the same as cars when they are designed and sold to the general public. When a car with a particular erray of extras or mods is produced for mass marketing it is vigorously tested and then 'type approved' to be sold to a certain spec. Some times optional wheels etc can be purchased from the dealer and these to are 'type approved'. If one then takes said car to halfords and fits different wheels, exhaust, lower suspension, high lift cam etc etc you are effectivly deriving a different car (along with voiding warranties). If you take your new van home and have a motor mover fitted, bigger battery etc you are altering the approved spec and, if you like. balance of the van. I would imagine motor movers on the front or back, gas bottles (one or two, size?) is going to vary from van to van, and your towing vehicle is going to affect wether you 'feel'it or not.

 

[Lutz]

I spoke to Powrwheel some time ago on the same subject and the answer I got was that their product works equally well whether ahead or behind the axles and that the space considerations could well dictate on which side the unit can be installed. This applies in particular to caravan chassis fitted with shock absorbers.

 

[Lutz]

Hi All

I would imagine vans are much the same as cars when they are designed and sold to the general public. When a car with a particular erray of extras or mods is produced for mass marketing it is vigorously tested and then 'type approved' to be sold to a certain spec. Some times optional wheels etc can be purchased from the dealer and these to are 'type approved'. If one then takes said car to halfords and fits different wheels, exhaust, lower suspension, high lift cam etc etc you are effectivly deriving a different car (along with voiding warranties). If you take your new van home and have a motor mover fitted, bigger battery etc you are altering the approved spec and, if you like. balance of the van. I would imagine motor movers on the front or back, gas bottles (one or two, size?) is going to vary from van to van, and your towing vehicle is going to affect wether you 'feel'it or not.

Not all components on the caravan as it leaves the factory are covered by type approval regulations. Motor movers are an example. The only way they could technically affect legal requirements is if they were factory fitted, in which case their weight would have to be included in the plated MIRO. (Obviously, as a factory-fitted item, they would also be covered by the caravan manufacturer's warranty rather than that of the motor mover's.) However, if subsequently fitted as an accessory item, they are treated just like any other piece of payload, like the clothes in the wardrobe or the contents of the fridge.

 

[ProfJohnL]

Hello Ian.

A 40Kg motor mover will increase the caravans all up weight by 40Kg, but it will not affect the tow hitch load by the same amount. This is because the motor mover will be mounted quite close to the axle on which it acts, and by the application of "Turning forces" only a small proportion of its weight will be transferred to the tow hitch.

The turning force (Torque) is defined as a force acting through distance on a pivot. The motor mover produces a force due to gravity of 40Kgf this acts on the axle through a distance of about 0.3M. This same torque is resisted by the tow hitch which is typically a minimum of 3M from the axle. Thus the equation is: NOTE This is only fully valid for single axle caravans

(Weight of mover x distance from axle) 40Kgf x 0.3M = 12Kgf/M (Torque)

12Kgf/M (Torque) / 3.0M (hitch from axle) = 4Kgf (effect on tow hitch)

This worst case scenario, as most moves are less than 40Kg, and the distance between the tow hitch and the axle is 3+ M both of these will reduce the effect on the tow hitch down force.

You also recognised if the mover is in front of the axle the nose weight increases, and conversely if the mover is behind the axle the nose weight reduces.

The fact that the mover is close to the axle and also very low down will minimise any affect on the outfits over all stability whilst in motion.

The balancing act on twin axle caravans is much more complex, which axle acts as the pivot? That depends on a myriad of factors which cannot easily be defined, this makes calculation of nose weights very difficult, and it is highly dependant on the flatness of the road surface, as bumps can make big differences to the actual imposed tow hitch load.

 

[Lutz]

You comments are all quite valid, John L, but I don't think anyone was suggesting that motor movers would be affecting the stabilitiy or handling of the caravan significantly differently whether mounted ahead or behind the axle. The effect that the motor mover has on the noseweight might suggest one location would be better than the other (if the noseweight was a bit on the low side before, it would be worthwhile fitting it ahead of the axle and vice versa) but on the whole and as supported by your statements, I would expect such considerations to be less important. The 4kg change to the noseweight that you calculated can be compensated, if necessary, relatively easily by other means.

What concerns me more is the effect that the movers have on the available payload. Some caravans already have a relatively small margin between MIRO and MTPLM and if you're going the add 40kg, that leaves you with 40kg less for all the stuff you're going to load on board.

 

[ProfJohnL]

You comments are all quite valid, John L, but I don't think anyone was suggesting that motor movers would be affecting the stabilitiy or handling of the caravan significantly differently whether mounted ahead or behind the axle. The effect that the motor mover has on the noseweight might suggest one location would be better than the other (if the noseweight was a bit on the low side before, it would be worthwhile fitting it ahead of the axle and vice versa) but on the whole and as supported by your statements, I would expect such considerations to be less important. The 4kg change to the noseweight that you calculated can be compensated, if necessary, relatively easily by other means.

What concerns me more is the effect that the movers have on the available payload. Some caravans already have a relatively small margin between MIRO and MTPLM and if you're going the add 40kg, that leaves you with 40kg less for all the stuff you're going to load on board.

Hi Lutz,

Thanks for your supporting comments. You are quite right, but my reference to stability perhaps was not as clear as it should have been, Ian had implied that you may need to move large heavy objects to compensate for the effect of the mover on the nose weight and in doing so you may compromise stability. By showing that the effect will probably be less than 4Kg in most instances, I was hoping to show that stability should not be affected too much.