Replacing Suspension and Hub units on a trailer.

graham

graham

Well-Known Member
Joined
16 May 2001
Messages
8,108
Visit site
i have a 4 wheel trailer for my Anderson 22.The design weight of the boat is 1350kg I dont know the weight of the trailer exactly.

The suspension units come complete with brakes and hub etc and are categorised by weight per pair.

Is it as simple as adding up the total weight then getting two pairs of suspension units rated at half each or do each pair need to be able to carry the full weight of the boatand trailer.

The larger capacity units are not much dearer than lighter rated ones.Is there any problem with getting units that are too strong?I would rather be well on the safe side.
 
It will not hurt to go oversize, only downside is, larger is stiffer hence harder ride next size up would be good.
 
The design weight may be 1350kg but, unless you're a hellava lot more disciplined than most people over what goes on your boat and what comes off before she goes on the trailer, I'd put money on the true weight being nearer 1500kg. If it turned out to be even more, I wouldn't be surprised.

One thing to consider - if only to dismiss it - is whether the stiffer ride from very oversized units would shake the rest of the trailer to the extent it starts to fail. It's unlikely, but if the construction's on the light side or the chassis rails are corroded, it could happen.
 
It does include the weight of the trailer. The chassis is suspended by the suspension units. You could argue that the hubs and wheels are unsprung weight and therefore not part of the equation. Trailer manufacturers I've spoken to tell me thet the lowest specified component on the trailer defines it's maximum capacity (Gross Trailer Weight) It's usually the tow hitch itself.
 
If the trailer is currently roadworthy, it would be well worth taking it (and boat loaded with everything you normally carry) to your nearest scrapyard or public weighbridge. Most scrapyards will at least verbally tell you what it weighs and their weighbridges are usually within 10kg of true weight. It only costs a couple of quid. At least then you'll know where you're starting from. Depending on where you buy your suspension units, be wary of the really cheap ones. You get what you pay for! Have a look to see if they have a decent nylon bearing in the outer end or whether they just rely on the rubber to preserve the suspension geometry. If you're borderline on weight, go for the heavier capacity units but if you're well within, I'd be inclined to stick with the lighter pair and spare your boat (and trailer frame!) the shock loads associated with very stiff suspension
 
I would suggest that your total weight will be about 1400 Kg plus about half ton for the sprung part of the trailer. So you need suspension units of 1/2 ton each. Don't go for excessively overrated suspension units as that will have less spring value. ie in extreme you might as well boklt the axle to the trailer with no springs. You should when towing get as much weight out of the boat into the car including O/B motor unless it is a very short road trip at low speed. Don't forget you need at least 10% total weight ie 200 kg weight on the tow bar. ie much too heavy to lift and a bit of a struggle with a screw down jockey wheel. This weight can be adjusted by moving the position of the boat fore and aft by moving the bow support post. regards olewill
 
I have to disagree with the nose-weight bit! Have a look in your car's handbook or on its EC Certificate of Conformity (if it is new enough to have one). It will quote the maximum nose weight you can put on the towball but even for very big cars, and MPVs it is usually between 75 and 100kg. I haven't seen any 4x4 ones and these might be bigger but I doubt it! If your car is post-98, your towbar should have the maximum noseweight stamped on the approval plate that is attached to it. I think it is called the "D" value. IF you go to France, I've heard stories about the French police doing spot checks on caravans and boats with scales under the jockey wheel and dishing out on-the-spot fines to people whose nose weight exceeds the maximum for the vehicle.
 
I agree with avocet and Howard. Have a good look around the NTTA site. It tells you all you need to know and avoids the "bar room lawyers" misconceptions.
 
Just realised you're on the other side of the world!

Here in the EC, the authorities have, in the last few years, got quite keen on trailers and towing. BEsides, I guess our vehicles are generally smaller than yours!
 
Thanks for all the advise. im away for a week or so now ,hopefully I can get motivated to make a start on my return.

I think for the all up weight 2000kg wont be far out.Im thinking of two pairs of suspension units rated at 1300 kg each.Theoretically this would give a capacity of 2600kg but I am concerned that going over bumps etc and braking the weight isnt allways equally distributed between the two sets of wheels. In fact going over the brink at the top of a slipway Ive noticed sometimes all the weight on one set.
 
That's OK, the rated weight carrying capacities are quoted for static weights on the understanding that they will go over bumps in use. I'd imagine they would be capable of carrying at least double the rated load instantaneously - probably even up to 3 times it!
 
High Avocet and all. Just researched the local RAC site they recommend no more than 10 to 15%.
My experience was with a large caravan many years ago when I loaded it to near balance. The driving was 'orrible with the van wanting to sway and nearly capsized or threw us off the road. By increasing the draw bar weight the situaltion improved a lot. The only way to eleviate the problem when driving was to accelerate as it was worse going down hill with the load pushing the car.
The limit on nose weight for a vehicle is probably related to headlight aiming as much as anything else. So don't drive at night with a large nose weight or readjust the headlights.
Here in oz we see at lot of load leveller bars on caravans. 2 bars with a right angle in one end are fitted into a fitting mounted under the ball. The aft end about 1 metre long is pulled up by chains to the trailer draw bar such that it all tends to lever the back of the car up and the front down. Another option is helper springs or adjustable compressed air dampers (shock bsorbers) all of which are designed to lift the rear of the vehicle to facilitate a large nose weight.
So I would recommend have a nose weight at the max for the vehicle or better fit these devices so that nose weight can be increased even further.
Of course ultimately by law the weight and capacity of the towing vehicle limits the towing weight. yes here in Oz towing is a way of life. Virtually all vehicles that are no mini type cars have a tow ball and a lot of people have caravans and or trailable stink boats . Many others regard a tow ball as accident damage protection. ( along with the bull bar) regards olewill
 
As already mentioned, the items in the boat / on the trailer add to the gross weight. You should also consider that when towing in wet weather quite a lot of water can collect in and on the boat. The ministry men just take the gross weight and don't care what makes it up.
 
Interesting!!!!

I've never seen one of those "load levellers" over here! In fact, I can't quite imagine them from the description! I don't suppose you'd have a website for a place that sells them over there would you? The reason I'm keen is because I have a big (well for over here anyway!) trailer myself and the back of the car is well and truly on its bumpstops all the time (even at the relatively modest nose weight limit my car allows)! If I have any less, however, it does tend to "sbake" a bit. As mine is a fairly obscure make of car, I can't get self-levelling dampers or helper" springs for the back, so these might be the answer!
 
Hi Avocet www.haymanreese.com.au have a picture of load leveller and can supply. in fact I think this outfits products are regarded as Rolls Royce of towing hitches in Oz I think they may be a branch or under licence to Reese in US but can't be sure. I have a cruder version which I had on my car for a long time but of recent years I don't tow very far or often so have removed it. Imagine fixing a lever to your car sticking out the back by 1 metre. Imagine jacking the end up in the air so you are trying to tip the car on it's nose. The end of the lever is actually pulled up on a chain to a point along the draw bar of the trailer. The bar is duplicated one each side and actually in my case has a rightangled leg of the lever which drops in to a casting clamped under the ball. The levers are able to swing left and right as you turn corners sometimes with a grating noise. I think the Hayman Reese system has a slightly different attachment to the fitting under the ball. olewill
 
Try fitting a Scott Stabiliser. They work very well, and are quite easy to fit. They increase the effective noseweight without actually changing it, so your car won't go any further down on the springs, and the friction element controls the trailer.
I've used them on trailers and caravans, they work. I think there are similar products from other manufacturers.
 
Thanks for that. I've actually got something very much like the "Scott" one you describe. It's called a "Snake master" and looks pretty much identical. The long spring steel blade, however, isn't there to lift the back of the car - it just exerts a gentle downward force on the plastic channel that it slides in so that when the car goes over a hump or down a ramp, the blade doesn't simply lift out of the channel. All the "anti-snaking" feature is in the friction disc. It works very well as far as stopping the snaking is concerned but doesn't lift the back of the car at all!

The other device that Olewill posted the link to is very interesting. Has anyone ever seen one of those in this country? I certainly haven't! I can see how that could lift the back of the car (if the attachment point was far enough below the tow ball centre and the arms were springy enough) but I can't see how it stops the snaking. It's not like it is altering the weight distribution of the trailer - its just pressing the hitch down harder on the tow ball! The same effect could be had by (effectively) putting a giant "G" clamp on the ball and hitch assembly so that it pressed down on the top of the hitch and upwards on the bottom of the ball. I'm intrigued!
 
You must log in or register to reply here.

Share this page

Top