On this third article of our Learners’ Information to Suspension collection, Robert Pepper discusses the variations between caravan and towcar suspension and the varieties of suspension present in caravans and trailers.
Your caravan wants suspension simply as a lot as your car if you happen to’re to have a protected and environment friendly tow. Identical to the towcar, the caravan has a physique and wheels. The wheels go over bumps, the caravan goes round corners and it slows down. All of this implies you want suspension.
The fundamentals of caravan suspension are the identical because the towcar; a spring absorbs the bump, and a damper (shock absorber) stops the ensuing bouncing. The springs and dampers are very related too. Caravans sometimes run coil, leaf or air springs. The dampers do the identical job too, and are of the identical design; twin-tube, monotube, foam and many others.
Variations between caravan and towcar suspension
There are, nonetheless, vital variations between caravan and towcar suspension. A driver will really feel poor suspension way more in a towcar than a trailer, and customarily, the suspension design in trailers is nowhere close to as refined as that within the towcar. You may usually see this whenever you comply with a rig over tough bitumen; the trailer will bounce, however the automotive received’t.
That’s the distinction in suspension design and high quality. The explanation for that is that the towcar could have had the advantage of plenty of engineering round suspension geometry, alignment, spring and damper tuning. The aftermarket will start with that rigorously engineered base after which tune for a given goal.
The trailer, alternatively, will most likely be an off-the-the-shelf chassis with off-the-shelf suspension, and on high is constructed regardless of the vanmaker likes. Regardless of asking, I’m but to see a lot proof of engineering dynamic design on caravan suspension – most appear to only bolt on shiny unbiased suspension and name it good, with simply a few notable exceptions who design their very own chassis and suspension distinctive to their vans.
It’s not a query of high quality, there are some very strong and well-designed suspensions on the market, it’s matching the suspension to the van itself.
Sorts of suspension in caravans
Caravan suspension will both be a beam axle, the place each wheels are linked to at least one axle, or unbiased, the place every wheel has its personal, shorter axle. Unbiased suspension affords dealing with and journey advantages in automobiles, however in trailers, the benefit is much less clear-cut. Once more, profiting from the tuneability of unbiased suspension requires vital engineering and testing.
The unbiased suspension does provide higher offroad floor clearance (photos above and beneath), however even the beam axle is prone to provide extra floor clearance than the towcar as its axle doesn’t have a differential or a driveshaft. General, unbiased suspension ought to, in principle, tow higher, however provided that it’s designed to be so for that particular van.
Many caravans run twin shocks …. why?
Many caravans run twin shocks, not singles. Why? Heavy vans run single shocks, so it’s not the load, even when leaf springs provide some damping there are a lot of heavy-duty coil-sprung vans and 4x4s with single shocks. There may be additionally little argument for redundancy; well-designed shocks hardly ever fail, and in the event that they do, you may nonetheless tow however the trailer will bounce – and every shock needs to be tuned to do half the work, so if one fails the opposite will shortly comply with as it’s then considerably overworked.
Additionally it is not true the caravan suspension does twice the work of the towcar. There isn’t prone to be twice the load, and for a single axle at the least because it’s a tripod, each wheels are extra involved with the bottom than the 4 wheels of the towcar.
This isn’t to say twin-shock suspensions by no means work; I personal a van with that design and it tows very properly. I’ve requested across the business and am informed {that a} large issue is price. Two small shocks may be procured for lower than a big one, even when it had been made, and likewise, two shocks appears harder.
From the customer’s perspective, don’t contemplate two shocks to be higher than one; the general engineering design and high quality of the parts are extra necessary. Nonetheless, people are inclined to fixate on “extra = higher = harder”. That is additionally what has pushed bigger and bigger shock tube sizes and remote-reservoir shocks, all of which may be offered at a premium, and 12,000lb winches the place 9500lb could be sufficient. Anyway, again to caravan suspension.
Caravans springs
Caravan suspension springs may be coil, leaf or air. Air has the benefit of self-levelling whenever you’re on the campsite, may assist with trailer hookup, and may be raised for offroad use and then lowered onroad. It’s costlier and never as dependable as plain metal spring, however dependable sufficient for nearly everybody.
Leaf springs are derided for his or her poor dealing with in automobiles, however in trailers, it’s a lot much less of an issue. I don’t assume there’s something improper with leaf-sprung, live-axle trailers and I personal one which tows nice. Nonetheless, advertising says unbiased suspension for caravans with shiny parts is what sells. Consequently, you’re unlikely to seek out a lot leaf sprung, however if you happen to do, then don’t assume it’s sub-standard or a poor tow. All of it relies on the standard of parts and engineering.
Loadsharing suspension
Some caravans have 4 wheels, not two, and these are generally known as tandems. The dynamics are fairly totally different between single axles and tandem axles because the singles function as a tripod, so the van wheels are all the time involved with the bottom. A tandem might need diagonal wheels within the air or unloaded. The tandem’s wheels additionally have to function in pairs on a facet; when the entrance left wheel goes up over a bump you don’t need the rear left wheel lifted off the bottom as which means much less grip and extra bouncing. This is the reason loadsharing suspension exists, and it appears like this:
When you intend to tow a caravan or trailer offroad, then you have to be utilizing loadshare suspension for higher stability and traction – braking and lateral grip. When you tow onroad, it’s much less necessary, however do be sure you tow such that the trailer is stage.
Modifications to caravan suspension are fairly uncommon in comparison with towcars, as sometimes, the van suspension can be designed for the job at hand. Most likely an even bigger consider ‘towability’ is weight and weight distribution. Heavy weights up high and at both finish will damage the towability of even the best-designed trailer, whereas weight central over the axles and low could make even a poorly designed trailer seem to be a towing dream.
In abstract …
So in abstract, your caravan has, and wishes suspension but it surely’s prone to be much less properly designed than that of your towcar. Shiny unbiased double-shock suspension isn’t the superb differentiator it appears, you’re unlikely to wish to change your van’s suspension, and if you happen to expertise towing instability weight, distribution might be the primary place to look except your van suspension is worn, or the van is way heavier than the makers envisaged.
