What Causes Fishtailing?

   / What Causes Fishtailing? #1  

Iplayfarmer

Super Member
Joined
Jul 11, 2005
Messages
5,316
Location
Idaho
Tractor
Massey Ferguson 1215, Case 801B
For some reason, my trailer decided that today was fishtailing day. I've had it loaded before with a similar load (2 tons of hay), but this time it would start to sway back and forth if I went any faster than 50 mph. In the extra 15 minutes that it took me to get home I found myself wondering why that happens. I know I've heard it before, but I've never really understood. Why do trailers fishtail?
 
   / What Causes Fishtailing? #2  
Too much weight on the rear will do that, often closely followed by staining of the shorts !
 
   / What Causes Fishtailing? #4  
I agree with Groundcover. Somehow you must have ended up with heavier bales on the rear. Tongue weight makes a trailer happy!
They sure make some pretty hay out there. The first self propelled bailer that I'd ever seen was in ID, Beautiful country up in the sawtooth's
 
   / What Causes Fishtailing?
  • Thread Starter
#6  
It could be that I had too much weight on the rear. I usually get small bales, but due to a shortage of that pretty hay, I'm taking whatever I can get. I had two 1800 pound bales. The first one was as far forward as I could get it, but the second still hung out the back a little.

So, what's the mechanism? Why does too much weight on the rear make a trailer sway?

I have new axles and a new tongue to put on this trailer as soon as I get some time, so the point may be moot (The new tongue is an A-frame, and I'll use an equalizer hitch). Mostly I'm curious.
 
   / What Causes Fishtailing? #7  
You need the weight on the rear suspension of the pulling vehicle to keep it from getting pushed back and forth sideways. When the front wheels are turned ever so slightly, that movement transfers to the trailer, and the trailer moves, lets the rearend of the pulling vehicle move sideways, and just makes more and more uncontrolled fishtailing.
But putting some weight on the tongue to hold the rear wheels steady is necessary....as you have learned and fortunately didn't have a disaster.
 
   / What Causes Fishtailing? #8  
I think it's some kind of voo doo geometry or something. (**** if I know) but anytime that I have loaded a trailer heavy on the rear it sways. If your trlr. does not have fenders it would be fairley easy to set your axles back a foot when you replace them. Some trlrs. seem to be to closely balanced, (esp. car hauling trlrs.) prolly for a light duty towing vehicle.
 
   / What Causes Fishtailing? #9  
You need the weight on the rear suspension of the pulling vehicle to keep it from getting pushed back and forth sideways. QUOTE]

I know what you're saying but, I've had a small trlr. (improperly loaded) sway, hooked to a dual wheel 1 ton. The truck didn't care. In other words the tail does wag the dog, just if it is an equal or smaller "dog::laughing:
 
   / What Causes Fishtailing? #10  
Boat trailers are especially bad about fishtailing because the majority of a boat's weight is in the rear.

On the plus side, at least on my two boat trailers, the suspension can be relatively easily moved fore/aft to help adjust the weight distribution...
 

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