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Trailer bounce


mikec
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Hi just wondering what people thought about this, I built a log splitter, but it bounces an awful lot on the road, even in motorways, pretty sure it gets air time sometimes too. Just wondering what people thought of the possible reason, it has rubber suspension, no idea if it's suited to the weight of the splitter as they were second hand, and it runs on mini wheels, I'm pretty sure there aired up about right, don't think I'd want any less in. So is it just the thing itself or could the suspension be too hard/soft? Cheers mike

Here's a pic

F51DC64F-30F0-49C3-B136-F9F64C819F1E-974

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Do you have any damping on the trailer suspension? You might find that the mass is perfectly resonant at certain speeds.

Otherwise, you could try running it with the splitter head at the furthest position from the towball, and see if it makes a difference with more weight over the wheels.

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No damping as such just the indespension units. I noticed it at first around town over potholes etc but towed it on the m/way the other day and it was as bad.

Its normally towed with the ram retracted, mainly because it's heavy ish on the nose weight for my Astra, plus it helps keep the ram clean :)

It's a heavy lump I can't lift the back end of it, unlike my small trailer which is very light, that bounces all over too when empty, but it's ok when loaded, I'm wondering if the suspension units are not up to the weight of it?

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One of my trailers does the same thing empty or loaded - it's got a very long extended drawbar to enable me to carry canadian canoe on the twin ladder racks. It's on those indespension units too - these were new a few years ago, and are 750kgs units. They're supposed to be self damping? It was running 13" wheels unit last year - they were badly perished, so went to 14" as they were available.

Although the tyres were new on a set of rims, I beleive they are the problem, with weak sidewalls, I'll go to reinforced 'C' rated tyres next.

Nice splitter btw. Was going to make a small trailer frame to mount my tractor 3 point unit onto to make it a bit more flexible.

Steve

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As you add weight it will get lower. The tyre should be roughly 10x as stiff as the springs, ie if you add 100kg, the suspension might move 10mm and the hub centre would drop 1mm. It sounds slightly over-sprung but quite under-damped, more on bump than rebound.

Some things to try:

1) measure the spring stiffness - add a known weight as above and measure the ride height and hub height.

2) somehow, "drop" the trailer and see what frequency it bounces at - how many cycles in five seconds, before the bounce dies away? That'll help point you at likely causes.

3) run it with the ram extended - sorry about the corrosion but it might make the problem go away?

4) After 1) and 2), you could either run lower-profile tyres, add damping or change the spring units.

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Get the trailer wieghed to give you an idea of susp. unit size needed, my guess is if they are old s/h units the rubber will be hard and not acting as either a spring or

damper . I'm not sure you would be able to get any smaller than 750kg unbraked anyway...

It probably sits at 150kg ish and tyre pressure should be set appropriately - a lower wieght would work with lower pressure and the tyres wouldn't overheat or wear

badly

My flatbed goes 1000kg ulw and if I'm towing a distance empty i run the tyres at 30psi then air up to 65psi before loading up

cheers

Steveb

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I was thinking of getting it weighed but as always no time, I reckon it weighs something like 300-400kg, I can't lift the main beam on my own. I'll try the above suggestions and see. I did buy some new 500 kg suspension units but the stub axles weren't the extended version so my existing wheels won't fit on. Cheers for the advice

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The load is quite far forward of the axle so you have to remeber alot of the weight of the trailer is on the hitch. If the trailer weight is say 300kg.. there may only be 200kg on the axle (at a guess from the picture). Thats only 100kg per wheel which the indespension units would hardly notice, especially when the rubber is old. It probably feels like there is no suspension at all knowing those things. Trailers are normally designed to almost be balanced on there axle(s), so wheel becomes the pivot point of the load. The way yours is set up I would suggest trying softer indespension units or something a bit more forgiving. or you could always lower your tire pressures even up to 30% for the weight that is on them. I would expect the trailer to behave alot better if you take some of the air out, so that the wheel wont bounce off the tarmac as much (the tire will absorb more of the energy as opposed to storing it)

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  • 2 months later...

Ok just a little update and question on this.

We got some weigh scales to do the vans at work so took the splitter in to weigh.

Results were

n/s/r 159 kg

o/s/r 182 kg

Jockey wheel weight 94 kg

Nose weight 83 kg

So roughly 435 kg total.

So the indespension units come in 350kg and 500kg.

So I need the 350kg ones right? As its the weight on the axles? I've no idea what's on it at the minute so I'm just going to buy some new ones

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Worth a phone call to your local Indespension dealer to check I'd say , do the 500kg units have brakes?

2x 500kg = braked. If not and the rating is per pair then the 350 kg should be fine , tbh just putting new low load

units on will probably make a big difference as the rubber does get hard over time

cheers

Steveb

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Worth a phone call to your local Indespension dealer to check I'd say , do the 500kg units have brakes?

2x 500kg = braked. If not and the rating is per pair then the 350 kg should be fine , tbh just putting new low load

units on will probably make a big difference as the rubber does get hard over time

cheers

Steveb

No hadn't thought of that the 500 and 750 ones don't have brakes so yeah must be per pair.

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  • 6 months later...

Hi mate its a Honda copy 13 hp engine, I'd have to check on the pump, but its not huge about 13cc possibly? I thought it was 26 when I bought it, or should say it was sold as 26cc. But it defo isn't, I looked up the number after I bought it.

From memory the outer body of the ram is 4" and the piston dia is about 2"

I worked out the pressures etc when I built it and its about 13ton I think.

I only have the engine on about half throttle when splitting, its not too quick, I don't think I'd want it any quicker as I've had a few near misses with it as it is! At a guess perhaps 6-8 seconds to go full travel of the ram, but in reality you only use about a foot of travel, I wanted a shorter ram to be honest, but trying to get one of the right size and price was a nightmare.

If you need any more info feel free to ask, I did do a build thread on another forum, ill see if I can find it.

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