Polyair and WDH

Submitted: Friday, Jan 09, 2009 at 12:28
ThreadID: 64955 Views:2109 Replies:3 FollowUps:0
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Hi all,

I previously, a while back now, posted in regards to using polyair type systems and Weight distribution hitches when towing a van.

Responses indicated several people used both systems.

Do you setup the pressure you want in the polyairs by hitching up the van without the wdh on, and then go from there? That is after determining your optimum pressure you then attach the wdh system.

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Reply By: Member - Graham H (QLD) - Friday, Jan 09, 2009 at 15:29

Friday, Jan 09, 2009 at 15:29
The instructions for the Polyairs say to PUMP THEM UP BEFORE LOADING.

Never load up and then pump them up.

I run mine at about 8lb empty and pump them up to 25 BEFORE hitching van on

The hitch will straighten the rig whether or not they are pumped up.
Always remember they dont alter the load in any way like a hitch they simply lift the back axle higher.

A hitch pivots the car and trailer to redistribute the load towards ends.
Polyairs simply lift what is directly above them just like a jack would.

I have since installed Progressive rear springs and last time I moved the van I didnt pump them up and it sat just fine anyway.


AnswerID: 343430

Reply By: DIO - Friday, Jan 09, 2009 at 16:54

Friday, Jan 09, 2009 at 16:54
Poly Air (and other makes) of airbag aren't really for 'lifting' the rear of a vehicle but to supplement the rear suspension. They do not increase your carrying capacity in any way and they are not meant to replace a WDH. One problem that you can run into when using them relates to the inflated pressure. If you inflate them to hard then they will/may prevent the suspension from actually functioning (as it should) when under load etc. This can result in excessive loads being transmitted to some suspension components which MAY result in failure (under heavy and excessive conditions). What's it all mean - don't overload your vehicle.
AnswerID: 343437

Reply By: Member - Toolman (VIC) - Saturday, Jan 10, 2009 at 08:40

Saturday, Jan 10, 2009 at 08:40
The answer is an emphatic NO! The polyairs are for dealing with the load in the back of your vehicle and not to assist with caravan.

Level you vehicle so that when fully loaded the back is at the same level as when unloaded i.e. measure the distance of the rear wheel arches to the ground on a level surface. Air is either added or removed from the polyairs to achieve this. From memory the polyairs should be pumped up when the vehicle is unloaded, and then the vehicle loaded, so you need to work out what pressure will need to be in the Polyairs to deal with the vehicle load. Then attach the caravan and level the van and vehicle using the WDH.

AnswerID: 343530

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