aluminum boat on galv. trailer bounces too much

[slowleak]

I've got a 14' aluminum boat that weighs about 430lbs on the trailer, the trailer is a 12" wheel galvanized bunk trailer with a 900lb GVW. Its the lightest trailer I could find for the boat.
All was fine till I replaced the tires, the original tires were Goodyear 4.80x12 LRB, The new tires are Kenda LoadStar LRB. I always ran the old tires at about 50psi, and they lasted fine. With the new tires, set at 60psi recommended pressure, the trailer bounces like a basketball all over the road. I tried lowering the pressure but makes little difference. The trailer is sprung light enough that I can stand in the boat and force the springs about 3/4 of their travel. Its not sprung hard at all. The trailer is dead level when on the hitch. I've tried moving weight around, no change. The trailer bounces so bad over rough road that he seats come dislodged from the boat. I don't dare leave the motor on the transom over the road. The first trailer wasn't a lot better, but it had 8" wheels, which were a ride quality issue on the long washboard dirt roads back to the lake.
I've looked in the rear view mirror and seen the trailer wheels several feet off the road even at low speeds in town.
The trailer suspension isn't bottoming out, it comes close but it don't touch. (I've used clay to check how close it comes to bottom over bumps. All this can't be good for the boat, the trailer, or even the truck or hitch. I've got a larger boat that tows fine, but its over 1500lbs on a heavier trailer. This boat, motor, and trailer is maybe 725lbs tops. The trailer is 220, the motor is 77lbs, the boat is 430 including a 32lb trolling motor and 70lb battery.
I've aired down to 30 psi and its better but still not good. The trailer is a year old. What I think is happening is the tires are rebounding before the suspension reacts. The roads are rough here but not so much that I notice it all that bad without the trailer.

 

[lckstckn2smknbrls]

Re: aluminum boat on galv. trailer bounces too much

How many leafs are in the spring pack? You may have to remove a leaf.

 

[UncleWillie]

Re: aluminum boat on galv. trailer bounces too much

The change in unsuspended weight has caused the suspension resonance point to move into the range that you drive a lot.
Without re-engineering the entire suspension system of the trailer...
The easiest solution would be to install an add-on Shock Absorber Kit.
Typically available for under $100.

 

[slowleak]

Re: aluminum boat on galv. trailer bounces too much

There are only two leaves and a short spacer or lower leaf about 4" long. The springs are no more than 500lb max each, you can't buy anything lighter and removing the second leaf would make them too soft. They're already super soft springs. I don't think the issue is the springs, its the tires, the old tires were softer even when fully inflated, these new tires are like a rock. The tire itself is bouncing, the suspension isn't rebounding, the springs don't bounce up and down, the whole trailer leaves the ground over even a minor bump. Any speed over about 10mph is enough to make it bounce off the ground. I pulled into the gas station the other day and thought the whole trailer was going over when I drove over the 1" curb at the gas station. The boat and trailer popped up so high I lost sight of it in the rear view mirror. It was never a smooth ride but with the new tires its now almost unusable. If all that's changed is tires, I have a hard time believing its a suspension problem.

 

[Maclin]

Re: aluminum boat on galv. trailer bounces too much

Did you change tires and wheels or just tires?

 

[smokeonthewater]

Re: aluminum boat on galv. trailer bounces too much

Shocks shocks shocks

 

[UncleWillie]

Re: aluminum boat on galv. trailer bounces too much

... The trailer is sprung light enough that I can stand in the boat and force the springs about 3/4 of their travel. Its not sprung hard at all. The trailer is dead level when on the hitch. I've tried moving weight around, no change. The trailer bounces so bad over rough road that he seats come dislodged from the boat... I've looked in the rear view mirror and seen the trailer wheels several feet off the road even at low speeds in town... The trailer suspension isn't bottoming out, it comes close but it don't touch...What I think is happening is the tires are rebounding before the suspension reacts...

....I have a hard time believing its a suspension problem.

The Tires ARE part of the suspension. More so on a trailer than a motor vehicle.
If you are bouncing all over the road, what else could it be.

Shocks shocks shocks

+3
It is amazing what a small set of shocks can do to calm down the wildest trailer.
I had a utility trailer that would bounce all over the place without a load in it.
After adding Shocks, I would get in myself in trouble because I would tend to forget I was towing anything.

 

[midcarolina]

Re: aluminum boat on galv. trailer bounces too much

seems there must be an issue with the new tires.........and they are magnifying the pogo affect of a light trailer/boat combo,

Bet others are correct that shocks will dampen the pogo affect

 

[loose rivet]

Re: aluminum boat on galv. trailer bounces too much

I've got a 14' boat on a 12' tire Bandit trailer, which was meant for a jet ski, it bounces all over the place on the dirt roads here. Several places where I fish have mile or longer roads leading to the ramp through the game preserves, any faster than 5 mph and the the boat and trailer will leave the ground. Smaller tire trailers are worse yet. Its not a matter of shocks, modern trailer tires in these sizes are too stiff, they don't give and the tire itself bounces, My trailer has a GVW of 800 lbs according the decal, the boat and gear are about 600lbs or so. The springs don't give at all, there's just not enough weight. I tried removing all but the main leaf and it did the same thing. The best fix is to let the air down to about 25 psi, any more and the tires just act like their on a trampoline.
A buddy actually dented the bottom of his boat, the boat and trailer weren't tight together and the bunks dented the hull. My old trailer had longer springs, which were more forgiving, the newer trailers all use shorter slipper springs.

I've never seen or heard of shocks on a trailer this small, it shouldn't be necessary.

 

[K-2]

Re: aluminum boat on galv. trailer bounces too much

Did you have the new tires balanced? Many people do not balance trailer tires, but a way out of balance tire / wheel could make
your light weight combo bounce around easily. If all you changed was the tires then it has to be the tires.

 

[roscoe]

Re: aluminum boat on galv. trailer bounces too much

crimp and solder

 

[midcarolina]

Re: aluminum boat on galv. trailer bounces too much

Or just pick up a couple ounces of dyna beads...or any other tire balancing beads, I use them on all my motorcycles and they work very well.... I think they were originally used in 18 wheeler tires

 

[BigDfromTN]

Re: aluminum boat on galv. trailer bounces too much

My guess is...

Reduce tire pressure or find more new tires with a softer side wall. Do they make Radial tires in that size? (I don't think so)

If the springs are not flexing, Shocks will do NO good. Shocks simply put just dampen travel of a spring in relation to the frame.

If it occurs at low speeds and when hitting bumps or holes. Its not a balance problem.

Looking back, I think you answered this question yourself. All was fine till I replaced the tires,

Best of luck!

 

[Okieboatguy]

Re: aluminum boat on galv. trailer bounces too much

I am voting for shocks, you mentioned that you think the tires are rebounding before the suspension can react and that you had some "Bounce" even with the old tires. You also noted that you are getting compression and spring from the suspension. A set of shocks should do it. It may not fix it 100%, and that is just due to how light the rig is, however, a set of shocks will dampen and absorb the "Spring and Jump" from the suspension that is caused by the tires rebounding. The job and design of a shock is to absorb the excess energy, which you seem to have an excess of.

 

[smokeonthewater]

Re: aluminum boat on galv. trailer bounces too much

My guess is...

Reduce tire pressure or find more new tires with a softer side wall. Do they make Radial tires in that size? (I don't think so)

If the springs are not flexing, Shocks will do NO good. Shocks simply put just dampen travel of a spring in relation to the frame.

If it occurs at low speeds and when hitting bumps or holes. Its not a balance problem.

Looking back, I think you answered this question yourself. All was fine till I replaced the tires,

Best of luck!

he very clearly stated that his springs were flexing so much that the trailer was almost bottoming out.

 

[UncleWillie]

Re: aluminum boat on galv. trailer bounces too much

he very clearly stated that his springs were flexing so much that the trailer was almost bottoming out.

+1
He is towing a Pogo Stick.
His springs would definitely appreciate a set of shocks.

... The trailer is sprung light enough that I can stand in the boat and force the springs about 3/4 of their travel. Its not sprung hard at all. ...The trailer suspension isn't bottoming out, it comes close but it don't touch. (I've used clay to check how close it comes to bottom over bumps. ...

 

[smokeonthewater]

Re: aluminum boat on galv. trailer bounces too much

Ya know, now that I think about it..... Just an educated guess here, but I BET he's also light on tongue weight..... The higher the percentage of weight behind the axle the higher the moment of inertia and the more it will bounce

 

[slowleak]

Re: aluminum boat on galv. trailer bounces too much

The tongue weight isn't adjustable but the wheels are pretty far back, there isn't much tongue weight but its double the rear weight judging by just lifting each end of the trailer.
I tried something today, if I lift the back of the boat and trailer up about chest high and drop it, it don't bounce, it falls dead, nothing moves. Yet at 10 mph over a driveway curb, especially if one wheel hits first, the second wheel will jounce two foot into the air.
It bounced around some with the old tires but those were old Goodyear tires, which are no longer made. I searched all over and the only tires I could find were Kenda Load Star or Chinese Carlisle USA Trail tires. The Kenda tires were in stock, they had to order the Carlisle tires but didn't recommend them. The old tires were soft and thin on the sides, the Load Star tires have thicker sidewalls. The max PSI on the Goodyear tires was 40 psi, the Kenda tires are 60 psi. I removed the boat and ran the trailer around a bit and it does the same thing, its even bouncing off the pavement even running down smooth highway.
The tires are not balanced, but I did check them on a bubble balancer my neighbor has and their within 1/4 oz of perfect. The rims and tires are new.
The springs are like new, its not a matter of something being stuck or frozen, and the simple fact that I've towed small boats all my life with no issues like this makes it hard for me to believe it needs shocks added. I've got another trailer, twice as heavy as this with springs so stiff they don't even bounce when you jump on the frame and it doesn't bounce around like this one does.

I have little doubt its the tires, but there just aren't any good choices out there to choose from. They do make radial tires but only in the heaviest possible tire rating LR-E. I bought LRB tires because they were the lightest rating I could find. The only choices I didn't consider were the oddball branded Harbor Freight tires and several super cheap tires which I only saw available in LR-C.
Last fall I towed a 12' boat back from FL on a similar trailer with no issues, but on smaller 8" tires. 70 mph most of the way and it never once bounced off the road like this. At the angle of approach with the springs and super hard tires I think the tires are just rebounding before the spring is forced to react. If the tires are softer, the springs seem to do their job, but I have concerns driving under inflated tires all the time. It can't be good for the sidewalls. I do notice that with the old tires, which are still on rims, if I simply sit on the tire, even with it inflated to its max of 40psi, the sidewalls are soft and they give, yet with the new tires, at 40psi, they don't move, they hold my 325lbs of weight as if they were solid.
They're definitely different style tires and no doubt too heavy for this rig.

 

[lckstckn2smknbrls]

Re: aluminum boat on galv. trailer bounces too much

Just for testing try adding weight in the boat over the axle.

 

[slowleak]

Re: aluminum boat on galv. trailer bounces too much

I'll try some weight tomorrow.
I did notice something tonight while moving the boat from the front garage to the shed outback. When moving the boat, motor an trailer around the yard, on asphalt, it bounces over every little rock or twig in the driveway. The tires also only leave an imprint of the middle line of tread when rolled through a puddle, the tread is crowned pretty severe even at 25 psi. The old tires were flat across the tread when fully inflated. I can also completely deflate the tires and they still support the weight of the whole rig. The old tires would go flat down to the rim. (I replaced the tires due to severe dry rot cracks).