Trailer swaying help.

[Lovey80]

I put the new home made trailer on its maiden loaded run from the Sunshine Coast up to Tuan over the Easter Break. This was the first time I had put about 1.6t in total over the Axles with the Boat, Camper, Fishing Gear, 150L of fuel on board.

I found that the trailer traveled really well on the highway and tracked perfectly when doing speeds up to 100km/hr. On several occasions when traveling down hill when the speed got up to around 110km/hr the trailer got a noticeable side to side sway up. On one occasion it could be felt in the tow vehicle.

Can the towing experts out there please give me the possible reason a trailer would get side to side sway only when hitting 110km/hr and going down hill?

[Noelm]

too much weight in the rear of the boat (not enough tow ball weight)

[Bros]

too much weight in the rear of the boat (not enough tow ball weight)

I agree the rule of thumb is aroung 10% on the ball.

[Chimo]

ditto, 150 kg min on the ball would be worthwhile to take the drama out of towing.

C
C

[ifishcq1]

Noelm, Chimo and Bros are all spot on
I jack knifed a 30ft 2t rig ten years ago and it taught me how to load a trailer
it blows me away when you see a van or boat stacked to the eyeballs at the back and nothing on the drawbar, swaying like a bitch it's a wonder more don't come to grief
cheers

[billfisher]

Firstly staying under 100kph and not loading up the rig with fuel and gear would be a good start!

As others have said you want sufficient weight on the towbar, ie 7-10%. Make sure you suspension and towbar can handle it though. Anti-sway or torsion bars would also be a good idea.

[googarra]

Its called the death wobbles in my area, all are spot on, more ball weigh by less load behind the axel set.

[SunnyCoastMark]

Hey........... ??? - No way am I calling you "Lovey" - people might talk (be good if you could let us know your first name? - for those of us who don't know it)

Yeah - agree with everyone above. Can you put up a photo of your rig - side view?

Sounds as though you might just need to move your winch post forward a little. Oh.. and where is the 150l of fuel located?

Mark

[ShaneC]

No need to redistribute your load, if that is how you want to travel with it, that is fine. You will however need to move your axles back a bit though. At the weight you state, I take it you have mechanical brakes, lets hope you have not cut the cables too short!! And being a new trailer there would be no seized U bolts etc so should be a breeze. Take your boat off the trailer, take the measurements and move your axles back a bit. The right distance can be calculated or just wing it.

I moved the axles back 120mm on my 4 tonne Noosa Cat, the guy who owned it before me never towed it so it was never an issue but when I first got it, the swaying was that bad that you were only on the road when you crossed it. I moved them back and jagged it right first time, no such dramas now and tow from Brisbane to Agnes on a regular basis, but I dont go as fast as you do. I have 430kg on the ball, but the F250 handles it fine. Hope this is of some help, even small adjustments make a massive difference so dont go too mad....

Shane

[tunaticer]

Also run a tape from the centre of your tow hitch back directly to your front spring hanger each side. They should be identical measurements.
Then check from centre of your tow hitch directly back to where the U-bolt goes around the axle, these should also be identical, if not one of your spring centre pins could be out or your U-bolt has moved marginally.
Usually the sway is created from load distribution, but these critical measurements can amplify its effect.

[Apollo]

Agree with the rest, but also include:
Checking tyre pressure on the trailer and vehicle
No water in bilge of boat sloshing around
No un baffled fluid (petrol) in boat
Weight distribution in boat to avoid making it top heavy.

[Fed]

With tandem trailers when the axles are independent of each other I think you need to get your towball height right to level the trailer when loaded before you worry about towball weight.

If the front of the trailer is low then the front axle starts taking more weight so the lower it goes then the lighter it gets, that's what I've found anyway.

I also think the 10% rule was an off the cuff post made by some goose at the start of the internet & has been perpetuated by googleboys ever since.
5% seems like a better number in my experience.

Hey Lovely, it's a sick feeling when they start swaying and the weird thing is when you try to correct the sway it gets worse.
People say to power out of it and I tried that once, at 140KPH there was still a slight sway and all I can say is thank God the downhill finished and the uphill started. Whew!

[Noelm]

Of course there is quite a few things that can cause a trailer to 'sway" but this post started with the boat being loaded with gear for holidays, so that being the case, we would think that too much gear was loaded to the rear of the boat, causing the rear of the trailer to be too heavy and start a pendulum action to start, this can be quite exciting if it gets real bad, the only way to eliminate this, is to load the gear in the boat to ensure the front still has a decent amount of weight on the tow ball.

[Lovey80]

Thanks for the replies guys. I was suspecting that the issue was one of two problems. 1 because of the weight issue stated and the second was that I thought that maybe the breaks on the trailer were not coming on at all under slight breaking/deceleration creating a want of the trailer to over take the tow vehicle and then it self correcting creating the sway or a combination of both. I plan on getting a new master cylinder either way as it doesn't seem to start to pressurise until a fair bit of travel.

Also once this started it could have been compounded by fuel sloshing side to side in the tank as I think the baffles are more to prevent front to rear sloshing. The fuel tank sits 50/50 over the axles and the camper(not pictured) that was sitting over the boat (in the grey posts) when we set off, are 50mm forward of the of the axles putting it's CoG slightly forward. We left the camper up at Tuan and came back with just boat and camping gear only (and less beer). Being that the camper gives (overall) more weight forward of the axles than with out, I anticipated the sway to get worse if the issue was certainly one caused by too much weight in the rear, but it actually got a little better.

The suspension is independent swingarm with coil springs and Polyairbags.

Remember that this only occurs once the speed gets in the 105-110km/h range.

[SunnyCoastMark]

Gee, sounds like a bit of a rig suspension wise. The camper top wouldn't help with the higher load position. (which would be why it got better) Aside from that - looking at the photos - I would be moving the boat forward on the trailer if possible. How much weight do you think is on the ball at the moment?

Mark