Trailer fish tailing????

[hammersley]

I have a 4x8 utility trailer with 15' truck tires. This is a new trailer! It starts fishtailing at about 70 mph, BTW more noticeable in the rutted sections of the freeway. I know that's fast, but I only have about 1000 lbs in it, with a 45lb tongue weight. This is not an extended tongue trailer.



What do you think is causing this? Question - will over inflated tires cause this or could the trailer not be aligned.

 

[Boldt's Wagon]

If I recollect correctly, they recommend about 15% of the total trailer weight (including trailer load) on the tongue weight to prevent fishtailing. If your trailer plus 1000 lb load is 2,000 lb total you should have 250-300 lb tongue weight, not 45 lb.

 

[RustyJC]

Not enough tongue weight. Be sure your trailer sits level when hitched and has about 12% of its total weight on the hitch.



Rusty

 

[Gary - K7GLD]

YEAH, what they said!

 

[roadranger]

Originally posted by RustyJC

Not enough tongue weight. Be sure your trailer sits level when hitched and has about 12% of its total weight on the hitch.



Rusty

Like he said: And if you're pulling with a 4x4, get yourself a ball hitch that'll get that trailer riding level. A high nose up condition combined with the single axle will tend to sway at high speeds.

 

[jimk]

fish tail

Every time I have a fish tailing experience it was caused by to little weight on the tongue. Now that I have a dodge diesel I have not had any more trouble. I have a 18 foot bed trailer which is very heavy and I have loaded up to where I did not wont to put any more as to put a set in the frame. I use reciever hitch that uses the overload bars like a travel trailer. This really works good for me. I made the trailer and I used the formula 18 foot / 2=9 foot + 18inches I measured from the frount of the trailer, not the tongue to the center of the springs. This may not be correct but it worked for me. lol jimk

 

[DMalone]

I had the same problem. What i found was the 1/8" OF PLAY in the receiver was causing the problem. Beleive it or not i couldnt get above 65mph or so and it started road walking real bad. I fixed it by taking two rachet straps and pulling the receiver tight on each side, this way the receiver would not have any play in it. You wouldnt think that little of play would had cause it but it fixed the problem for me. I could run 100mph if i wanted to and no road walking at all. Worth a try it fixed mine. good luck.

 

[Henry]

Is jimk's formula correct?

If I can jump in on this, I have a question about axel placement. I see jimk used 1/2(length of box without tongue)+18" for spring centers. Is this correct? If so, I'm assuming the trailer load must be evenly distributed. If that's the case, is 18" behind the loaded balance point the way to calculate axel placement?

 

[MJawsman]

Ditto on tongue weight, but check your trailer tires. Are they ST (service trailer) rated? If not, I'd recommend that you get or at least try a set. Passenger car or even LT tires lack the sidewall strength that a trailer tire has and can contribute to sway. It may not be all of your problem, but it may contribute to it.

 

[RustyJC]

Originally posted by MJawsman

Ditto on tongue weight, but check your trailer tires. Are they ST (service trailer) rated? If not, I'd recommend that you get or at least try a set. Passenger car or even LT tires lack the sidewall strength that a trailer tire has and can contribute to sway. It may not be all of your problem, but it may contribute to it.

ST-rated tires are not available for a number of sizes used for large trailers. For example, our 13,500 lb GVWR 5ver uses LT235/85R-16's, just like our 3500. This 5ver has a 12,000 lb GAWR and runs 10,800 lbs on the axles when fully loaded.



Many other large 5vers use LT tires from the factory as well.



Rusty

 

[MJawsman]

Originally posted by RustyJC





ST-rated tires are not available for a number of sizes used for large trailers. For example, our 13,500 lb GVWR 5ver uses LT235/85R-16's, just like our 3500. This 5ver has a 12,000 lb GAWR and runs 10,800 lbs on the axles when fully loaded.



Many other large 5vers use LT tires from the factory as well.



Rusty

Your are correct, of course. But as this thread originally started out with a problem on a 4x8 utility trailer, who knows what kind of tires are on it.

 

[RustyJC]

Originally posted by MJawsman

You are correct, of course. But as this thread originally started out with a problem on a 4x8 utility trailer, who knows what kind of tires are on it.

10-4 - no problem. I just didn't want someone to think that ONLY ST-rated tires should be used on ALL trailers (i. e. , to take what you said as a blanket statement). No offense intended.



Rusty

 

[MJawsman]

Originally posted by RustyJC





10-4 - no problem. I just didn't want someone to think that ONLY ST-rated tires should be used on ALL trailers (i. e. , to take what you said as a blanket statement). No offense intended.



Rusty

None taken!

 

[jbone]

Bet if you put another 100-200 lbs on the tongue

your problem would go away--can't balance those

trailers--they need tongue (weight)..... R, J. B.

 

[redramnc]

Henry,

I have always heard that 1/2 box length plus 1" back for every foot of box is the way to locate the axle centerline. This provides a reasonable amount of unloaded tongue weight.



Of course, unless the load is symmetric and can be centered on the trailer, you have to pay attention to how the load is sitting and how much the truck is squatting as the load goes on.



The above 'Rule of Thumb" is just that. I have a gooseneck with a 20' deck that has the axles a good bit further back than the rule says (deal was too good to pass up). Due to major tongue weight it pulls like a dream even when the weight is not balanced but does it load the truck rear suspension real quick once the weight gets in front of the axles.



Check out a manufactured trailer to see how they located their axle(s). Most of them seem to be balanced well.

 

[jeepit]

Get it level and 12% of trailer weight on ball and you will be good to go!!