How Much Rear Weight Causes Fishtailing ... ?

nickap

Member
Sep 17, 2017
75
Just came back from a great camping trip to Cape Cod ... I had a scary experience on the way down there though -- my first incident of fishtailing. I was sailing happily along the highway, probably a few MPH faster than I ideally should have been, but had never had any troubles before so I'll admit that I wasn't being as careful as I should. At one point I felt a slight left-right motion of the steering wheel, which went away after a second or two. But 15 minutes later it happened again, and this time, over just a few seconds it went from very slight to almost completely out of control. Trying to keep the wheel straight, I saw in my mirror that the PUP was slewing wildly from side-to-side ... Never having experienced this before, I didn't know the "approved" response but I braked as smoothly as I could while trying to keep the wheel straight, and once the trailer brakes kicked in and I lost a little speed, the PUP quickly came back in line. You can imagine I drove much more carefully, and several MPH slower, after that.

So this is obviously a case of inexperienced driver being stupid and careless -- definitely a learning experience for me, I'll absolutely keep my speed down from now on. But it did make me wonder what exactly caused the fishtailing on this trip, and not on previous ones, since admittedly I had probably also driven at times faster on those trips than I should have. There was a little wind the day of the Cape Cod trip, which may have been part of the problem, but it wasn't severe. The only other difference was this: for once, I had pre-cooled my fridge properly before the trip, and so instead of bringing all my stuff in a cooler and then transferring it to the fridge later at the campsite, I put some of it in the fridge before I set out. It wasn't much - a couple of bottles of ketchup etc., some veggies, some eggs, cheese - basically I can't imagine that it could have been more than a few pounds. The fridge is at the very back of the PUP though. Could such a small amount of additional weight in the rear cause the PUP to fishtail? I've seen people saying that a bike rack on the rear can do it, but this had to have been much less weight than that ... I'd be interested to get folks' opinions; I can keep the fridge empty when on the road if necessary, but it would be helpful to know that I could safely put a few things in there if necessary ...
 

GreyFox

Super Active Member
Oct 10, 2018
2,447
S Ontario
Could such a small amount of additional weight in the rear cause the PUP to fishtail?

Nowhere have you indicated that you've weighed your trailer loaded & ready to camp nor have you indicated that you've measured the trailer's gross tongue weight, loaded & ready to camp. Without knowing both of these numbers there's no way any one of here can definitively say what caused this sway you've experienced. Obviously you want to keep the trailer's GVW loaded & ready to camp within the trailer's GVWR and load it so the trailer's gross tongue weight (loaded & ready to camp) around 13% to 14% of that gross weight.
 

mattlreese

Active Member
Sep 6, 2017
231
Sounds like you had too much loaded in the rear of the popup. Try shifting the weight around. You can also get a friction anti sway bar and you would need a new hitch receiver. I have one and have never experienced any sway with over 5k miles towing. I tow with a Pacifica minivan.
 

jmkay1

2004 Fleetwood/Coleman Utah
Oct 10, 2013
7,393
Northern Virginia
What could also cause sway is the tunnel effect that sometimes occurs if a big rig was to pass by you or you go through a valley between mountains. I have also had extremely bad roads where say your popup hit a pothole and want to go in a different direction. Sway is a very scary thing and a great reminder to always keep aware and to drive slower. Do weigh your full setup and get your actual tongue weight. Even the lightest thing could cause sway if you already are on the low end.
 

J Starsky

Super Active Member
Aug 3, 2017
1,167
East Central MN
You could have a bad bushing in your leaf springs causing steering input! That could be unrelated to load. Inspect your suspension 100% before placing the blame just yet [B)] We had a jeep that did that to us once, dude tossed a bunch of steering parts into it before we notice the eye bolt moving inside the shackle when loaded... Good luck! [8]
 

Sjm9911

Super Active Member
May 31, 2018
11,499
Nj
You got lucky. All the advice up above is right on. Do all those things. Especially the small sway bar. Additionally, if the trailor starts to sway, hit the manual break controller in the tv , and step on the gas. This will straighten out the camper.
 

FARfetched

Active Member
Nov 22, 2018
743
Sector 706, Planet Georgia
My son (RIP) ran a moving business. He said he had a situation where the trailer (26' moving trailer) started swaying… he hit the button on the brake controller, and gassed the TV, and it straightened right out. Pretty much what Sjm9911 said.

To avoid such incidents in the first place, make sure the trailer is loaded properly with the proper tongue weight. If you have your manual, it will tell you what the proper tongue weight is. If not, 10% of the total trailer weight should get you in the ballpark.
 

nickap

Member
Sep 17, 2017
75
Thanks all - some very good lessons here. Mainly re. the weight distribution; I will definitely adjust how the camper is loaded and will measure my tongue weight before my next trip (not till next year now, unfortunately). After reading a little more about fishtailing, I had figured out that hitting the manual button on the brake controller would be the best way to deal with it if it happened again - but adjusting the weight should help avoid that. I have also ordered a sway bar which should help. Appreciate all the help!
 

Halford

Super Active Member
Sep 28, 2011
3,563
Santa Clarita, California
No sway bar is needed. just do the weight distributing by moving heavy stuff to front toward tongue and light stuff in the rear. This will solve the swaying issues. I do the same with all 3 old popups and now Airstream. It is funny because many Airstream owners have WDH which includes sway control because they have not done weight distributing well. I keep mention it but only a few AS owner listen. There are a few AS owner not using WDH or Sway control equipment because they know the secret of solving swaying issues.
 

Sjm9911

Super Active Member
May 31, 2018
11,499
Nj
Thats all well and fine, but what about the 18 wheeler that passes you at 85 mph and creates a wind gust that starts your trailor swaying? Packing corectly is good, but it cant help with everything.
 

Sjm9911

Super Active Member
May 31, 2018
11,499
Nj
The sway bar they say cuts down on the turning radius, i never had to take it off to back it in. And never had it effect the turning. If anything it prevents rookie Jack knifing. I havent seen any wdh on pop ups.
 

Toedtoes

Super Active Member
May 28, 2018
2,840
California
I have the sway bar on my FnR. It drives me nuts. Finally realized it was why I had so much trouble backing the trailer into the driveway - I need to make a deeper angle than the anti-sway wants me to have. Took it off on the way home this last trip and was much happier the entire drive.

Now my FnR is a bit odd with its "no load hitch" - those castor tires under the tongue help prevent sway and provide a smoother ride than I've felt with other trailers. So, I'm not too concerned about dumping the sway system to make backing up and turning easier.

As said above, looking at your entire load and where it sits is the important thing. Also, consider the full weight of the trailer. A trailer with a loaded weight of 1500lbs should have a tongue weight between 150 and 225lbs. Additional food of 10-20lbs shouldn't be an issue. But if your loaded trailer is 900lbs, then 10-20lbs of food can definitely affect the 90-135lbs of tongue weight.

Speed, winds, vehicles passing, road conditions,etc., can all affect sway as well. And yes, your tow vehicle's steering system can make a difference also.
 




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