Does a suspension lift increase front axle load on your caravan?
Reader question:
Hi Robert, I have had a number of conversations with people regarding rear suspension upgrades to reduce sag and improve stability when towing a caravan. I use a weight distribution hitch to restore front axle loading when towing. Many people think that a suspension lift with a 300kg constant load will improve stability. My argument is that it levels up the rig but doesn’t restore front axle load and wdh is still required. Am I correct and have you done a video that addresses this specific issue?
They may be right in theory, or maybe not, but not in practice.
Raising, and presumably stiffening the suspension will increase the height of the towball above the ground, which all else being equal, will have a small effect on the towball mass. The effect will be less on tandems than single axle, and it’ll be opposite. With a single, the effect will be to fractionally reduce towball mass, with a tandem, it’ll slightly increase.
However, any effect will be small and the WDH will make a much, much bigger difference.
Just because the car looks level doesn’t mean to say the weight distribution has changed. I think that’s the misconception.
This video is the closest to what you need explained.
5 Comments
by dave
Hi Robert,
your measuring with fixed axle on the trailer. Tandem SHOULD be load sharing axles (most vans are these days, and must be if ATM exceeds 2T) so one point of pivot point, not 2 separate as you demonstrated & acknowledged in your video. Your explanation for tandem trailers applies only to poorly engineered tandem trailers – not load-sharing axles.
Perhaps you should run the test again with a proper tandem or triaxle trailer.
Good points about the wheelbase to towbar overhang though. A lot of people dispute it, but the car rear wheel scales dont tell fibs, and neither does the resulting loss of ride quality (for same configuration vehicle & trailer).
by Robert Pepper
I didn’t know that tandem should be load sharing – got a link to the ATM? Lot of illegal trailers out there then. I rarely see load-sharing, I did mean to mention it but forgot. Thanks for the reminder. And yes loadshare is one pivot point.
by chris
not true. they don’t have to be load sharing at all but they should be in my opinion as it kinder to the trailer and the road. don’t believe me check the vehicle tech stands bulletin 1 building light trailers which is the rules in australia.
many large vans and trailers now have independent suspensions on a swing arm set-up which is much better than the old slipper springs idea. with a coil spring for each swing arm, some of these even use airbags instead of springs (which could be made loadsharing)
the al-ko independent system uses a rubber torsion bush(its probably not actual rubber but a urethane).
by Dave
Hi
Thanks for the video and the load calculator it has been very useful in a confusing world.
If a weight distribution hitch is added to the setup, will it help reduce the rear axle load where your calculator says it will be exceeded ?
by chris
nope. they actually add weight via spring pressure yes they do put some force onto the front axle but that is transferred through the chassis of the vehicle. they add force to the rear suspension first.
they can even make things worse and cause bending of chassis especially if incorrectly selected or fitted and adjusted incorrectly.
usually this happens when you go through a gutter, ditch or washout and especially if the rear of the vehicle is already heavily loaded or for a ute has a lot of tray behind the axle with too few body mounts (early ranger models were like this, I know of someone that happened to and he wasn’t towing he simply had the ute loaded to its max regularly as a spraying contractor. ford fixed the issue on later models by adding extra body mounts and plating the chassis)
long story short the only thing that fixes overloading is leave some gear behind or if only a few kilos over say under 20kg is rearrange your gear to change the weight balance. ask your self do i really need all the wizz bang gear or can i get buy with less. choose a alloy bull bar and roof rack instead of steel etc. if travelling as a group do we all need to bring a gas bottle etc and can some of the gear travel with someone else. yes that ties you together as a group but it means combined you can stay longer or be better equipped.
trailers should be loaded that the trailer carries the load not the vehicle But you still need to have a slightly forward of centre weight distrobution so its stable to tow and there is a bit of load on the hitch and it doesnt need to be 10 percent studies from europe have proven this 5 percent is adequate for most trailers. what is most important is weight balance. you dont want liquid tanks at the rear that sloshing liquid is a problem