Thread: Is independent suspension that much better than leaf spring?

Hi folks,

We have a campomatic with independent coils. Had it for a few years, and I think it was built maybe 1996, the first of them with coils. I think they used Alco rubber torsion before that.

I haven't taken it on rough bush roads but have driven on rough 'cobbly' bitumen, the type that in a 60 series cruiser gives young the s....ts. The camper rides as smooth as, on these roads whilst the towing vehicle does its stuff, bouncing along (Disco TD5, Subaru Forrester, Nissan X Trail). The camper would be the smoothest ride in these conditions. I have no idea how it would hold up on long distance rough outback roads though.

Cheers, Simmo

I don't know why you'd want to tow a trailer with independent suspension behind a truck with solid axles, and I know which I'd prefer to repair in the field But why doesn't someone make a solid axle with coil springs
Dave

Originally Posted by David Hawes

I don't know why you'd want to tow a trailer with independent suspension behind a truck with solid axles, and I know which I'd prefer to repair in the field But why doesn't someone make a solid axle with coil springs
Dave

As pointed out in an earlier post - the principal drawback of coils is that they place the suspension load at a single point instead of two points. This means either a heavier or more complicated chassis design. I suggest this may explain it!

John

IMHO it is difficult to fit a decent set of coils under a camper, without either making the axle too low or lifting the camper too high.

We have had experience with trailers, both with a S1 Disco rear axle housing ends, one with leaf springs and shocks and the other (boat trailer) with the the suspension set-up of a Series1 Disco, coils, trailing arms, A frame and shocks, all at the same angles.

The boat trailer tows way better, both on rough terrain and corrugations, the ride is even much smoother than the tow vehicle, which is pretty good. Also, other than replacing the occasional shock, and regular greasing of wheel bearings, we haven't touched the suspension in about 150,000kms







excuse the poor pic - very dusty and smoky from burning off





Erich

Originally Posted by David Hawes

I don't know why you'd want to tow a trailer with independent suspension behind a truck with solid axles, and I know which I'd prefer to repair in the field But why doesn't someone make a solid axle with coil springs
Dave

You'd have to tow one to find out. I think the guys at Tvan who make trailers for the military know a thing or two about trailers and their setup is awesome. Try a properly set up independent set up off road and you'll know what I mean

2 major problems with independent axles on trailers, or anything really is that the more load you put on the lower your centre clearance becomes. In theory you could load an ind. Susp. (IS) to the point where the centre underneath is actually sitting on the ground.
Also when under load and an axle (wheel) travels upwards (over a rock, say), the pivot point of that IS axle travels in an opposite direction. Laws of Physics For every action there is an equal and opposite REACTION.
A straight beam axle with leaf springs will ALWAYS have the same ground clearance, C/L of axle stub to ground, depending on the height of the tyre and wheel, also less pivoting parts and a bush leaf spring ain't hard to rig, try repairing a snapped pivot point on IS in the scrub, Regards Frank.

2 major problems with independent axles on trailers, or anything really is that the more load you put on the lower your centre clearance becomes

All independent suspension camper trailers ( I have seen) have much MORE ground clearance than leaf sprung trailers. Also because they are camper trailers the suspension is usually pretty stiff so that people can walk around in them. The lowest point on mine by far is the spare wheel underneath, and it can only be where it is because it is independent.

The main benefit of independent , in my Camp'o'matic anyway is no skipping on corners at all, and no skipping on corrugations at all.
Mine is over engineered with parallel bearings with a load rating of 1500KG.
While there are more solid axle campers out there I have only ever seen failed solid axle campers never independent , maybe because there are many more failure points on a solid axle in spring centre bolts, u bolts, and shackle welds to frame. Shackle weld failure is the most common failure point according to the Coen RACQ recovery bloke, and he knows!

It is far easier to under specify a solid axle than an independent, as the parts are easily obtainable from any trailer parts supplier, so dodgy builders build to a price, while independent is usually part of a complete chassis and sold as part of an upmarket model.

I only once saw a photo in a 4WD magazine of a Camp'o'matic being limped home on a piece of timber on one side, and I thought how could that happen, and the answer must have been total neglect, as the parallel bearing must have seized so tight it ripped off the stub axle.

All things being equal there is not that much difference except the independent being IMHO better on corrugations IF the solid axle is specified and maintained properly with regular checks of shackle welds, ubolts, centre bolts and main spring fatigue. Of course bearings should be checked and repacked or replaced before every long trip with both independent and solid.

Well my independent is now 17 years old and I should replace the springs as the paint is blasted off and I replaced the Koni shocks last year before yet another lap of OZ. The only potential failure points apparent on mine are the weld for the stub axle ( and this applies to solid) , the pivot bushes and they would only cause the alignment to be lost, and the coil spring, and if one broke the trailer would still be towable.
Regards Philip A

So Philip are you saying that I/S trailers do not lose ground clearance when loaded or travelling over rough or rutted ground, esp at the pivot point.
Because with a solid axle with leaf springs the lowest point is the c/l of the axle, you can also buy axles that don't have welded on stub axles as they can be machined onto the end of the axle bar. When a wheel on a solid axle travels up over, say a rock, then the tray of the trailer does the same, increasing ground clearance.
The lowest point on my C/T is the bottom of the axle which would be about 30mm below the c/l of the stub axle. (Springs sit on top of axle and U_bollts have nuts on top)
Most independent swinging arm setup w/coil spring and shock I have looked at have the bottom of the suspension arm level with where the rim and tyre meet and most were badly knocked about underneath.
To each his own, I suppose, Regards Frank.

Originally Posted by PhilipA

All independent suspension camper trailers ( I have seen) have much MORE ground clearance than leaf sprung trailers. Also because they are camper trailers the suspension is usually pretty stiff so that people can walk around in them. The lowest point on mine by far is the spare wheel underneath, and it can only be where it is because it is independent.

The main benefit of independent , in my Camp'o'matic anyway is no skipping on corners at all, and no skipping on corrugations at all.
Mine is over engineered with parallel bearings with a load rating of 1500KG.
While there are more solid axle campers out there I have only ever seen failed solid axle campers never independent , maybe because there are many more failure points on a solid axle in spring centre bolts, u bolts, and shackle welds to frame. Shackle weld failure is the most common failure point according to the Coen RACQ recovery bloke, and he knows!

It is far easier to under specify a solid axle than an independent, as the parts are easily obtainable from any trailer parts supplier, so dodgy builders build to a price, while independent is usually part of a complete chassis and sold as part of an upmarket model.

I only once saw a photo in a 4WD magazine of a Camp'o'matic being limped home on a piece of timber on one side, and I thought how could that happen, and the answer must have been total neglect, as the parallel bearing must have seized so tight it ripped off the stub axle.

All things being equal there is not that much difference except the independent being IMHO better on corrugations IF the solid axle is specified and maintained properly with regular checks of shackle welds, ubolts, centre bolts and main spring fatigue. Of course bearings should be checked and repacked or replaced before every long trip with both independent and solid.

Well my independent is now 17 years old and I should replace the springs as the paint is blasted off and I replaced the Koni shocks last year before yet another lap of OZ. The only potential failure points apparent on mine are the weld for the stub axle ( and this applies to solid) , the pivot bushes and they would only cause the alignment to be lost, and the coil spring, and if one broke the trailer would still be towable.
Regards Philip A