Advice Needed On Axle & Spring Sizes for Tandem Trailer

[Dave666]

I will soon be doing a major refurb on a tandem trailer purchased recently and not sure about axle and spring sizes.

I estimate the total weight fully loaded (including trailer) to be between 1600kgs and 1700kgs. Currently the old axels are 40mm square each and springs are 3 leaf slipper springs (I think rated to 600kg a pair).

While nothing is broken on the current set up, I think whats on at the moment is a bit small? I was considering two 45mm axels and 5 leaf slipper springs rated 900kg a pair. While I thought this would be a better set up, I am worried I am going over board and concerned the trialer will jump / skip around.

Can annyone provide some advice please.

Thanks
Dave

[finga]

Have a look in this cattledog.
In the springs and axle section they give weight specifications
http://www.activefabrications.com.au/documents/activecataloguejan05%20v2.pdf

Lots of other stuff there too for a full refurbish.

[bigjimg]

Gday Dave,If you go for a setup that provides a 15-20 percent margin above what you require there should be no problem.I have 3 ton setup on my work trailer and it is rated only for 2 ton.There is no tendency to skip around any more than what the 2 ton gear have,as compared to my last 2 ton trailer.Jim

[Dave666]

Thanks Finga & BigJim,

Its seems a bit strange that the trailer has operated fine, and drives well, with small 3 leaf rated to 600kg a pair (tandem = 1200kgs) but if I go for the 5 leaf which are rated to 1000kg a pair (tandem = 2000kgs) thats nearly a 100% increase in size!

Using your method of total load + 15% buffer the 5 leaf calculates to be the right spring, but my head tells me to split the difference and go the 4 leaf which is rated to 900kg a pair (tandem = 1800kg). Hmmmmm - not sure.

Same problem with axle selection. Currently 40mm square on the trailer and no issues, but 45mm makes sense.

I have a habbit of going overkill, with most things its fine, but I worry the trailer might bounce / skip with the bigger springs.

Cheers
Dave

[johncar]

hi Dave, I would not hesitate and use the 5 leaf, 45mm axle setup. You wont have any issues with it bouncing around or anything. You were lucky to get away with the old setup as it is too light for 1600 - 1700kg as you know.
Conservative general rule of thumb for for dual slipper spring tandem axles is: based on 5 leaf 1000kg per pair to double the load minus up to 20% due to to non load sharing factor of this type of setup. That would give you a safe spring load bearing of about 1800kg and remember that is your safe maximum while new, they will of course take more but if you don't problems, best with an understressed system.
As far as the axles go, by going up to the 45mm it allows you to use the larger ford style slimline bearings giving you a dual axle rating of around 2700kg.
The 40mm axle would also do the job too but for minimal extra cost it is certainly worth the larger axles and bearings. 40mm axles at the length required on many boat trailers force them to be fairly long and also making them prone to flexing and therefore need to be derated somewhat to be safe, they are more suited to narrower lighter trailers.
Hans at Probar Caboolture is one of the best people to speak to in this regard, he has heaps of experience and information. I have always gone to him for advice and trailer needs.

[Dave666]

Hi Johncar,

Thats good advice - thank you. I wanted to keep the current 13inch alloy rims, which are curently on 5 stud early holden hubs that also need replacing. If I went for th 45mm axle, I dont think I can use the Ford Slimline bearings with early holden hubs?

Cheers
Dave

[Noelm]

there is a couple of things that need to be considered when dealing with a tandem trailer with slipper springs, they are NOT "load sharing" meaning that if you are going over a driveway and there is a "hump" (like all servos and probably your house as well) the wheel that is on the hump has 100% of the load, unlike a rocker setup that shares the weight, this sudden (and brief) over load can, and does, bend the shit out of slipper springs (trust me I know this first hand) and the probelm is muliplied when cheap Chinese springs are used. Go for heavier springs if you are staying with slippers, or talk to a "proper" spring manufacturer.

[johncar]

Hi Johncar,

Thats good advice - thank you. I wanted to keep the current 13inch alloy rims, which are curently on 5 stud early holden hubs that also need replacing. If I went for th 45mm axle, I dont think I can use the Ford Slimline bearings with early holden hubs?

Cheers
Dave

Hi Dave, Yeah there is no worries with getting the Slimline bearings in the early holden stud pattern hubs for your current rims. As Noelm said that is correct at any one point in time with double independent slipper setup you can have the whole weight on one or the other axle and therefore wheel and it would probably only cost about $50 more for a 45mm axle setup giving you a more robust job. Confirm with Hans at Probar, but pretty sure he has HT holden hubs with SL bearings and marine seals.
Load sharing suspension is always best but yes the cost will go up a bit, but if you stick to your basic setup then you have to consider derating the tandem springs perhaps more like 25% bringing you closer to 1500KG for your dual 5 leaf ones at 1000kg per pair. And you shouldn't experience and skipping around with the heavier system. Try and achieve about 10% of the total BMT weight downward on the ball when all loaded, being about 160kg on your rig, that should give good stability underway.

[SunnyCoastMark]

Hey Dave,
Basically - you want a 2000kg rated set up. You can go with 40 square axles, but if you are using slipper springs - you will need 45mm axles - to give you 20% more rating - same thing with your tyres and springs.

I would not recommend load sharing or rocker springs for two important reasons:-

1) Maintenance - there are numerous moving parts which must be able to move in order to work correctly. Immersing regularly in salt water - even with a hose down after every trip, will see you having to strip & grease/ clean your suspension far more than you would like.

2) If you have a flat tyre for whatever reason - you must stop immediately to repair - and they always go in the worst place - at the worst time. This is because both axles are joined via the rocker springs - the wheel/axle will drop on that side. With slipper springs, it is quite safe to continue driving (carefully) until you reach a safe or convenient place to fix the flat. In emergencies - you can drive as far as you need to - with due care.

We have had customers with hire trailers (furniture vans; car carriers etc) drive hundreds of km's with out even realising they had a flat tyre.

I have just modified/refitted a trailer for my own boat - 6.5m Trojan (BMT - 1600-1700kg) and used 45mm Round axles (less weight than square) Mecahanical Over ride Disc brakes with Jap slimline bearings and 6 leaf slipper springs.

As with any set up though - maintenance is always the key

Mark

[Noelm]

while I don't for one minute dispute what Sunnycoast has said, I have had both rocker and double slippers a couple of times, and both have some advantages, but I reckon the rocker setup is the best, even in salt water, the slipper is so simple and easy to look after, but the rocker is superior in every way (in my opinion) not too sure about the flat tyre bit though, I had a flat with my rocker setup and din't even know untill I stopped.

[Dave666]

Big thanks to all - great advice.

You have put my mind at ease about going with the bigger set up (well - bigger than what it currently has). I am going to run with 45mm axle, 5 or even 6 leaf slipper springs, HT hubs with SL bearings. I will try to get as much in Gal as possible.

Just on that. Should I get the axle in gal, but someone will have to grind off the gal to weld the brake flange on, or just get standard axle, weld the flang, then hit it with Cold Gal? Any preference.

Once I have refurb the running gear, rollers and electrics, my idea was to hit it all (except the new gal fittings) with a wire wheel, paint it in cold gal, then go over that with tectyl. Sound right?

Cheers
Dave

[johncar]

Galv axles are ok, but yeah you will have to grind some of it off for welding as you say and reseal those areas. It can be a bit of messing around ordering them also a bit more cost and at the end of the day, a good coating of suitable sealer is good too and can be touched up easy enough down the track.
Tectyl is Ok too but does get a bit messy and after a few years of recoats, the trailer gets a bit cruddy looking and a big job then to strip it all off, been there. Tectyl would be better if just used on the axles but maybe not on the whole trailer and I don't like it on springs, I prefer just to spray a bit of Inox around the springs and trailer, protects, lubricates and doesn't seem to build up and lasts for a fair while . The only thing with it I notice that it tends to desolve some types of cold galv coatings, but usually ok on killrust and other paints, just need to test it on any painted areas first. Inox is not so suitable for long term use around natural rubber products either so best to avoid, but Lanox should be OK on natural rubber.