Most caravanners probably don’t consider the additional stresses imposed by towing on their vehicle’s suspension.
Even with a relatively light ball load of about 180kg, a tow vehicle can suffer from ‘front-end float’; that is, the front of the vehicle bobs up and down over bumps. It is actually pitching fore-aft, but because the rear suspension is loaded down with the van on the back, it doesn’t feel that way. Clearly in this situation there is less weight on the front-end of the vehicle, but a weight distribution hitch (WDH) is not necessarily the answer. After all, while WDHs have their place, they are a mixed blessing. There’s no other way to increase the weight over the front wheels but to use a WDH, and vans with particularly heavy ball loads (that can’t be reduced by better distributing the load inside the van) may well require a WDH.
However, most caravanners who use a WDH do not realise that they are supposed to release the spring bars when driving over terrain that involves a significant change of angle, which includes spoon drains, as well as when driving in offroad conditions.But another way to improve the pitching scenario described above is to fit heavy-duty dampers (shocks) at the least. While replacing the front dampers will yield the most benefit, it is a good idea to also replace the rear dampers with heavy-duty items, to allow the vehicle to better cope with the load imposed. Not all heavy-duty dampers make the ride rock-hard; often they are of better quality than the original-equipment dampers and provide a ride that is better controlled.
In addition to dampers, heavy-duty, taller springs (typically 50mm taller) should be considered for a 4WD that has been fitted with heavy gear such as a steel bullbar and cargo drawers. Although a vehicle not equipped with these heavy items would benefit from heavy-duty rear springs when towing, ride quality can be abrupt when driving unladen.This does depend on the quality of the components; if you fit a good 50mm lift kit (comprising springs and dampers) from a reputable company, it will be a better-controlled ride while still being fairly supple when driving unladen.
AIRBAG HELPER SPRINGS
Caravanners often choose airbag helper springs for the rear suspension to level their vehicle when towing. Airbag helper springs can work really well here, but only if the ball load and vehicle payload are not excessive. If you have 250kg-plus on the ball and your tow vehicle’s cargo area is chock-full of heavy gear, you might be tempted to pump up the airbags beyond their maximum pressure. In this case, you would be risking the chassis cracking on your tow vehicle.
Additionally, you won’t restore mass to the front axle as you would with a WDH (a suspension upgrade does not reduce the weight imposed on the rear axle by a caravan) so the rig might be still unstable when towing. You might also end up exceeding your vehicle’s maximum rear axle rating, too.
Airbag helper springs don’t work as well in some leaf-spring setups (such as in some 4WD dual-cabs); if the vehicle’s leaf springs are already on the firmer side, the airbags will make the ride even more abrupt, even when deflated to their lowest permitted pressure.
THE BOTTOM LINE
The only way to restore weight to the front of the vehicle, once a caravan is hitched up, is to use a WDH, but they won’t solve other suspension problems. If you want to level the ride and reduce fore-aft pitching, an aftermarket heavy-duty suspension might be the answer, provided you do your homework and ensure you buy a quality kit that is known to work well in your vehicle.
AL-KO’s Independent Rubber Suspension has made such an impact on the Australian caravan scene. Read the Independent Rubber Suspension Guide to find out more.