What Causes Fishtailing?

[woodsmith]

I've only fishtailed a trailer twice.

First time I had a SWB Land Rover with a twin axle car transporter carrying a VW bug. The hitch on the Land Rover was too high and not adjustable. Hiched up the trailer front axle was off the ground. That fish tailed at about 55mph but with an old Land Rover there wasn't anything left to accelerate out with so I held out as best I could and let it slow down to below 50.

The second time I took my car and box trailer to pick up some concrete paving slabs locally. When I got there and opened the trailer doors I realised that my last load, a huge settee, was still in the trailer. As it was raining I left it in there and put the slabs behind it knowing it would be tail heavy. However, what the heck, it was only a mile or so down the road.:thumbsup:

That set up was fish tailing all over the place and I only got home crawing at 5mph and stopping everytime it went sideways.
When I went to unload I opened the back doors and placed my foot on the trailer bed to help lift the first slab and the back wheels of the car left the ground!:confused2: :laughing:

No wonder it was fish tailing so bad. Definately a nose/tongue weight issue.:laughing:

 

[PILOON]

I had a 3/4 ton PU and 5 x 9 trailer and a contractor friend offered to 'fill me up' for like $20. with nice garden soil.
OK, but he REALLY filled me up, even packed it down with his excavator bucket!
Plenty of power to pull OK -BUT when I headed towards the traffic lights I just plain ran out of brakes, down shifted (1st not syncro) as best as I could, prayed for the stop light to change all while looking where I might do the least damage should the light not change in time.
Lady luck was with me! The light changed in time.
Tell you the ride home was real slow.
A wire to the electric brakes was cut. (not that I was overloaded- much)
Lesson learned, but I had no sway!-, no wonder, springs were just about bottomed out.

 

[slowzuki]

a) need a better controller that tells you if the brake circuit is cut. Prodigy is a good fair priced model.
b) always do a brake check when leaving loaded, this is when you adjust your braking gain on the controller.

I had a 3/4 ton PU and 5 x 9 trailer and a contractor friend offered to 'fill me up' for like $20. with nice garden soil.
OK, but he REALLY filled me up, even packed it down with his excavator bucket!
Plenty of power to pull OK -BUT when I headed towards the traffic lights I just plain ran out of brakes, down shifted (1st not syncro) as best as I could, prayed for the stop light to change all while looking where I might do the least damage should the light not change in time.
Lady luck was with me! The light changed in time.
Tell you the ride home was real slow.
A wire to the electric brakes was cut. (not that I was overloaded- much)
Lesson learned, but I had no sway!-, no wonder, springs were just about bottomed out.

 

[77bronco]

I'm planning a full rebuild on this trailer including new axles, new wheel wells, and a new tongue in the very near future, so I haven't been the most diligent about maintenance of the current axles, tires, etc.

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

 

[Diamondpilot]

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

I agree.

Its even cheaper to buy a trailer then build one.

Back in 2003 I needed a new trailer to replace the monster 25+5 25,000 GN. Though my connections I got a 18x82 tandem trailer for under $1,000

Axles, 4 tires, springs, steel, and nothing else cost over that. I still needed paint, wood for the deck, lights and electrical, ect. I don't know how they can do it.

Chris

 

[Iplayfarmer]

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

I agree.

Its even cheaper to buy a trailer then build one.

Back in 2003 I needed a new trailer to replace the monster 25+5 25,000 GN. Though my connections I got a 18x82 tandem trailer for under $1,000

Axles, 4 tires, springs, steel, and nothing else cost over that. I still needed paint, wood for the deck, lights and electrical, ect. I don't know how they can do it.

Chris

I already have the brake axles and coupler (I got them pretty cheap through a friend), and there are some things I really like about this trailer. I like that it's narrow, and I like that it's a tilt deck. I thought about selling this one and building a new one with the axles I have, but it would cost me more to buy the steel than I could get out of this one. The only real unkown at this point is the fenders. The new brake axles have a little more drop to them, and I'm afraid my wheels will be uncomfortably close to the tops of the fenders.

 

[Reg]

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?

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

 

[Iplayfarmer]

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

That explains the uphill phenomenon.

 

[art]

Those big square bales are what got you! At least the one on the rear!!! You can bring a flat bed trailer to it's max capacity with big square bales! And yet you could take a drop deck trailer of small squares and still not max the load out!

You had to much weight on the rear of the trailer is all the problem you had and your lucky you realized there was a problem before there was more of one!

Good driving!!!

Through the years I've had the pleasure of towing many things with trucks that were inbalanced. Disc harrows, and then with tines added to the rear, cultimulchers, that could only be towed at 20 or less and they would wip like crazy at that!! At 17 years I hit both sides of a bridge with a cultimulcher at 20mph!!! That was less then 1/4 mile from starting point! Found I could lift the back of the truck off the ground while I was thinking about the thirty miles I had to go!

 

[mbrule]

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

Very Interesting.....

I think that perspective helps explain my swaying camper, due to the placement of the axles on the camper there is only about 400 lbs tongue weight (7k trailer), which is nothing for my 3/4 ton pickup. So, I cannot get a and b at the same time....

Sorry did not mean to hi-jack, but I like your explanation, simple and makes sense!