Leaf spring and solid beam axle,V/S Independant coils and shockies ?

Submitted: Friday, Nov 18, 2016 at 20:17
ThreadID: 133791 Views:8293 Replies:8 FollowUps:10
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Have had a guy in my ear all day that is adamant leaf spring and solid beam axles is superior over independent supension on corrugations, What do you think?

Cheers Axle.
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Reply By: RMD - Friday, Nov 18, 2016 at 21:13

Friday, Nov 18, 2016 at 21:13
Probably it is best to find out the credentials of the person saying technical stuff.
Leaf springs of short, high curvature design are not much good.

Earlier Jayco Outback leaf springs on independent suspension were horrible and caused axle failure.
Similar springs on a beam axle would have done much the same.

The flexibility and ability to absorb bumps is better. Longer leaf springs will do that and when fitted to a beam axle are quite good.
So, what does he mean? What combination is he referring to?
Without knowing the situation no one can really give a realistic opinion.

Cruisemaster independent susp does ok. An Alko unit which has the spring mounted between the Pivot of the independent arm and the axle has to have a far less forgiving spring and so will ride harder. Not sure why they made it that way.

I was advised a 6x4 trailer can't survive the Oodnadatta track. Seen many which didn't.
On my trailer I fitted 60 series modded front springs to a 50mm square axle and also fitted shocks. The trailer rode beautifully both loaded and empty. It has compliant suspension which absorbs bumps. Lasted the Oodna track and other places to. Still working well 24 years later.

Most leaf sprung landcruisers lasted ok but suffered from having too much axle mass for some corrugated roads. Proper design of Independent also do well and are/may be superior. All depends on the understanding incorporated in design of the items.
AnswerID: 605999

Reply By: splits - Friday, Nov 18, 2016 at 22:31

Friday, Nov 18, 2016 at 22:31
Utes have become very popular as tow cars these days and just about all of them have an independent front suspension and a solid axle leaf sprung rear suspension. Both ends of the car seem to handle corrugations without any problems.

It all comes down to design. Cars are well designed and are constantly being improved while most caravans look the same as they did fifty or more years ago.

Have a look at this link dynamics. particularly the section mid way down the page and headed " roll centre and roll axis ".

The trailing arm system as used in caravans and trailers tilt the wheels over at the same angle as the van. Cars that have used trailing arms use the semi trailing design. It changes the angles and toe in/toe out of the wheels in corners.

If I was to buy a van I would want a hollow beam axle to reduce unsprung weight and long leaf springs set up the same way as cars only with a slightly higher rate.

There is a good reason why car manufacturers have continued to use long leaf springs mounted with the front eye down low and the rear shackles up much higher in everything from cab/chassis utes, sedans and sports cars since the 1950s.
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Follow Up By: pop2jocem - Sunday, Nov 20, 2016 at 10:13

Sunday, Nov 20, 2016 at 10:13
That sounds like my favoured setup

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Reply By: gbc - Saturday, Nov 19, 2016 at 07:31

Saturday, Nov 19, 2016 at 07:31
He's drunk. And the link above has zero to do with corrugations.
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Follow Up By: splits - Saturday, Nov 19, 2016 at 20:27

Saturday, Nov 19, 2016 at 20:27
" And the link above has zero to do with corrugations."

I think it has a lot to do with corrugations. Corrugations can give an uncomfortable ride and they can shake a van to pieces but they can also result in the wheels loosing constant contact with the road. That is vital for stability and braking.

Then there is the issue of how each one handles in corners. I have seen plenty of corners with corrugations.

This all comes down to the van having the best suspension design that today's technology can provide but are we getting that in most of today's vans?

The original question was about which type is superior. It did not ask in what way.
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Follow Up By: gbc - Sunday, Nov 20, 2016 at 06:30

Sunday, Nov 20, 2016 at 06:30
Having towed both and driven both there is still no argument as far as I am concerned. There's a reason why pretty much every high speed off-road race vehicle runs independent. Sure a poorly designed 21 foot van incorectly loaded on corrugations around a corner too fast on independent suspension is going to struggle. You'll never sell me that a leaf and beam 4wd does anything at all better on currugation than independent. Cycling quickly is what independent suspension does well.
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Reply By: 2517. - Saturday, Nov 19, 2016 at 09:14

Saturday, Nov 19, 2016 at 09:14
Spoke to a large manufacturer of hard floor campers about this ounce and he view was springs are better, the biggest problem with independent suspensions is people tow them to fast and bend things which have to be returned to the factory to be repaired.Saw 2 vans on Gibbs River Rd with this problem, people just sit up in the Landcruiser and roar a long.
AnswerID: 606008

Follow Up By: Shaker - Saturday, Nov 19, 2016 at 09:37

Saturday, Nov 19, 2016 at 09:37
That's because a lot of the independent suspensions fitted to campers & caravans are fairly agricultural compared to Track Trailers MC2 suspension, or Vista RV's which is even better.

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Reply By: The Bantam - Saturday, Nov 19, 2016 at 11:29

Saturday, Nov 19, 2016 at 11:29
I think the guys view is over simplistic.

First of all are we talking about cars or trailers?

It matters little the issues are pretty much the same, except there are two particular issues that differ in trailers.

1/ the suspension on trailer does not need to be as sofisticated or as well designed on trailers, because the trailer does not corner, handle and brake on its own.

2/ suspensions on trailers are all pretty much without exception crude in comparison to similar suspension that would be found on stand alone motor vehicles.

Issue 2, is pretty much THE overwhelming problem with trailers ....... regardless of the type of suspension, the majority of suspension systems fitted to trailers are utter rubbish.

Even the very best trailer suspensions commercially offerd are piss $#@!% poor compared to the best systems available on stand alone motor vehicles.

All suspension systems have their advantages and disadvantages.

Leaf springs and beam axles.
The biggest advantage of leaf springs and beam axles is that it is very easy to engineer an adequate suspension system ...... what I mean is a suspension system that will perform tolerably well.

Pretty much the entire worldwide heavy transport fleet rode on leaf springs and a beam axle until the advent of airbags ..... pretty much all light commercials have a beam axle at least in the rear.

All engineering requirements for a pretty decent leaf spring and beam axle suspension are very well known, easily dealt with and all the parts are redily available.

The problem with leaf springs on trailers is that ..... even though all the information required to make leaf springs and a beam axle perform well is readily available ....... most trailers with leaf springs have fundamental flaws that can not but ensure they perform poorly.

they are

Failure to mount the springs in a proper attitude

The almost indemic use of spring rates that are far too hard.

the use of short springs

the failure to fit shockabsorbers

the failure to fit bump stops and properly deal with the suspension running out of travel both at the upper and lower end of suspension travel.

Coil sprung independent suspension

Should in theory be THE best available suspension for pretty much any purpose other than carrying heavy loads.
This is why it will be found on pretty much all high performance cars, both on & off road and in both general use & competition.

The basic engineering of independent suspensions had also has been very well known and documented. While computer design and simulation has allowed some significant improvements in function and comfort ..... the basics of independent suspension is not rocket science ....... most of it can be well understood with year 12 maths and geometry.

The problem with independent suspension on trailers comes from exactly the same source as beam axle suspensions ........ the inherant crappiness of trailer suspensions in general.

those problems are

Failure to mount the springs in a proper attitude.

Failure to select propper spring rates

Realy crude and most disadvantageous swing arm geometry

Frequent failures in the designs of the swing arms and their attachment points.

Short swing arms

A failuure to actually build and attach the suspension securely and squarely to the trailer

Poor shock absorber design ... not matched to the spring rate and the load

Frequent failure to mount shockabsorbers in their designed attitude

Failure to properly deal with the suspension reaching the end of travel at both ends.

I know there are some independednt suspensions for trailers that some think are wonderfull ........ but put beside the suspension found in stand alone vehicles they all look piss poor.

Oh and we do not see the wide variety of suspension systems we see on stand alone motor vehicles ....... beam axles and coil springs, leaves and independent, dual training links, double wishbones, semi-independents and so on

pretty much all of this is due to trailer builders failing to get past the idea of attaching whatever cheap suspension direct to the bottom of a flat trailer box. rather than designing the trailer chassis and the suspension as a whole

As it stands it's not the type of suspension that is the issue it is the adequacy of its design

AnswerID: 606009

Follow Up By: Member - Bigfish - Saturday, Nov 19, 2016 at 18:36

Saturday, Nov 19, 2016 at 18:36
Agree...But the worlds best suspension is useless if you do not air your tyres to suit conditions. Tyers also are part of the suspension system.
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Follow Up By: The Bantam - Sunday, Nov 20, 2016 at 17:43

Sunday, Nov 20, 2016 at 17:43
especially if your springs are over stiff
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Reply By: Member - TonyV - Sunday, Nov 20, 2016 at 13:25

Sunday, Nov 20, 2016 at 13:25
Money no object go independent air.....

Kimberley independent suspension and why.

AnswerID: 606026

Reply By: Echucan Bob - Sunday, Nov 20, 2016 at 13:49

Sunday, Nov 20, 2016 at 13:49
Theoretically, the lower the unsprung weight the better. ie independent suspension with allow wheels (with tyres running low pressures) should be best, and also ask less work of the shock absorbers.

I have a car with a solid front axle, and a car with IFS. Both handle corrugations very well, from a passenger ride perspective. However, the solid axle car managed to destroy a pair of newish Bilstein shock absorbers after a few hundred kilometers of corrugations.

I think the main advantage of a solid axle is allowing greater articulation and hence ground contact by all four wheels in uneven conditions. However, traction control systems consign this advantage to the dustbin of history. Modern vehicles, like the later Discos will proceed with only two wheels on the ground.
AnswerID: 606027

Follow Up By: The Bantam - Sunday, Nov 20, 2016 at 18:06

Sunday, Nov 20, 2016 at 18:06
In fact. in theory there is no articulation advantage to a solid axle ....... look at the competitive off road buggies ...... that have independednt suspension with extra ordinary amounts of travel in the suspension.

Most of the time when a solid axle 4wd is modified for greater articulation it suffers dramatically in wheel control ...... the geometry gets all out of whack and the location of the axle in the chassis get pretty sloppy.

If you look at many of the independednt suspension systems for trailers , the arms are heavier than the combined weight of the leaf and beam axle they replace.

I continue to maintain that it is easier to build a tolerable suspension using a leaf spring and beam axle, but if all known engineering is applied an independed suspension will be superiour in all aspects.

Problem is and especially in trailers ....... very little of the available engineering is applied to the task.

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Follow Up By: Echucan Bob - Monday, Nov 21, 2016 at 07:19

Monday, Nov 21, 2016 at 07:19
Bantam, I agree with what you say. In trailers the solid axle doesn't need to weigh much at all compared with the independent system (just a length of 50 mm steel), but in the tow vehicle the solid axle includes diff, drive shaft etc so is quite a bit heavier than Independent systems.
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Reply By: Malcom M - Monday, Nov 21, 2016 at 06:53

Monday, Nov 21, 2016 at 06:53
For the trailer market, you'd be hard pressed to find a manufacturer who really knows how to design independent.
It has become a 'buzz word' and with the marketing hype required to constantly sell new trailers, everyone now must have one.
Very few buyers would ever question the design of whatever rubbish was fabricated in their nice shiny new buzz word trailer.
AnswerID: 606043

Follow Up By: 08crd - Monday, Nov 21, 2016 at 11:13

Monday, Nov 21, 2016 at 11:13
I think you have pretty well summed it up. There is nothing wrong with solid axle and leaf springs, easy to design, simple and very structurally sound.
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Follow Up By: Malcom M - Monday, Nov 21, 2016 at 11:28

Monday, Nov 21, 2016 at 11:28
and you can get parts practically anywhere plus you don't have to muck about with castor/camber adjustments which will go out on corrugations.
Also a whole lot cheaper...

Just lacks that buzzword capability for when you are bragging around the campfire.
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