Trailer shockies – another angle?

Submitted: Tuesday, Jun 21, 2005 at 09:43
ThreadID: 24042 Views:4679 Replies:7 FollowUps:5
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Hi guys,

Made the decision to fit shock absorbers to the trailer and being an inquisitive mind got to wondering about the mounting angle. Appreciating that a lot of variables are at play with this question just wanted to focus on the angle.

Not being an engineer I have worked out that a shockie mounted perpendicular to the axle would work a lot harder than one mounted horizontal, which would provide no dampening at all. I’ve looked at a lot of trailers and there is no consistent approach, this I presume has more to do with lack of knowledge, cost, available parts used rather than optimum performance. So based on this, I presumed that the closer I get to a horizontal position the less dampening will occur.

I want to deal in only a forward or rearward angle installed on a standard leaf spring system. It is a retro fit and some aspects are fixed (such as the mounting possibilities). It occurred to me that at some stage the angle becomes so fine that dampening becomes minimal.

My questions are is it beneficial to have even minimal dampening rather than none? Is there a point of zero value (say that a 45 degree angle offer a 50% dampening – only guessing, sure it is more complex than this)?

Anyway any input would be appreciated.

Kind regards
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Reply By: Moggs - Tuesday, Jun 21, 2005 at 10:56

Tuesday, Jun 21, 2005 at 10:56
Why not just fit rebounders to the leaf springs and forget the shocks??
AnswerID: 116671

Follow Up By: Member - Beatit (QLD) - Tuesday, Jun 21, 2005 at 13:49

Tuesday, Jun 21, 2005 at 13:49
Hi Moggs,

Your probably right and I am a believer in the KISS principle. But a notable ex GMH suspension engineer member of this forum convinced me on shocks. Took some convincing I'll tell you but his argument was a good one that I could not ignore.

Kind regards
FollowupID: 372208

Reply By: Well 55 - Tuesday, Jun 21, 2005 at 10:57

Tuesday, Jun 21, 2005 at 10:57
You raise a good point in positioning of shocks on a leaf sprung trailer. Look at the rear springs on say a leaf sprung L/C and the top shock mount is towards the C/L of the vehicle, which to my way of thinking would work better than one in front or behind the axle.

AnswerID: 116672

Follow Up By: Member - Glenn D (NSW) - Wednesday, Jun 22, 2005 at 20:18

Wednesday, Jun 22, 2005 at 20:18
Not an expert and prepared to be corrected ,but , if mounted at the same angle the shock should do the same work .

ie the rear hilux shocks one forward one aft .

in theroy they should have the same travel if at the same angle

FollowupID: 372453

Reply By: robak (QLD) - Tuesday, Jun 21, 2005 at 11:00

Tuesday, Jun 21, 2005 at 11:00
Not an engineer either, so just having a fguess here.

A shockie at 45 dgrees would need to be 1.41 times "stronger" to give the same effect as a perpendicular shockie. So, being stronger, but working with the same forces means it should last longer.

The same shockie at a 45 deg angle will offer 70.1% of the dampening of a perpendicular one.

AnswerID: 116673

Reply By: Member - Peter- Tuesday, Jun 21, 2005 at 11:37

Tuesday, Jun 21, 2005 at 11:37
Hi Beatit,
I'm not an automotive engineer either, but I think it would be more important to compare the amount of travel between the axle and the shockie first and then work out what angle you want. eg. if the absolute max. travel of the axle is 200mm (just to pick a figure) and the limit of travel in the shockie is 100mm, then the angle between the vertical and the shockie should be at least 60 degrees. You can work out the travel in the shockie by calculating cos of the angle, ie. in the above example, cos 60deg = 0.5. I think this is important because you don't want the suspension bottoming out on the shockie ie. the shockie reaching the limit of travel before the suspension reaches the bump stop.

I suggest you need to measure the maximum travel in the axle, from the lowest point ie. when the trailer is effectively "lifted in the air" to the highest point ie. when the suspension is fully compressed to the bump stop and make sure the angle in the shockie allows the travel in the shockie to cope with the above max movement. You may be able to get the max travel measurement from the trailer manufacture.

Just as a example, if the angle between the vertical and the shockie is 30deg, the shockie travels 0.87 times the suspension (cos 30 = 0.866) and 45 deg = 0.71 times.
AnswerID: 116685

Reply By: Member - Matt Mu (Perth-WA) - Tuesday, Jun 21, 2005 at 13:26

Tuesday, Jun 21, 2005 at 13:26
Its all about the shockie!! It totally depends on the manufacturers design as to the correct angle for the 'best' dampening effect, while taking into acount wheel travel etc.
Have a look at the difference beween an early Rover to a Torsion bar front end. The difference is near on 80deg!!! But the difference in dampening effort between the two shocks is huge and it has to be, because of where the designers put the shocks in the first place!

If you want a set of purpose shocks for a camper trailer, have a look at the ALKO website!!! Shock at 45deg, gives good dampening and complete wheel travel!

ALKO Shokie Kit
Just ignore the fact the shock in the pic is upside down...fitted these a few months ago, what a breeze and what a different trailer ON THE ROAD!!!
AnswerID: 116710

Follow Up By: Member - Beatit (QLD) - Tuesday, Jun 21, 2005 at 13:45

Tuesday, Jun 21, 2005 at 13:45
Thanks Matt,

Looks a good setup alright and I for one would never claim that I'd even come close to understanding the dynamics of suspensions.

From my earlier trials I have found out that I dont like the single pin type fixtures on shocks in trailers. I have broken a couple mainly due to the shock resistance being greater than the strength of the chasis - the shock ripped out a piece of the chasis where the mounting pin was welded (good weld but insufficient strength in the steel). The shock at no time would have maxed out in this set up.

Both failures were on below aferage country roads, not even on a Cape like corrugation.

I believe in the merits of high tensile bolts through a hanger (like at the ends of leaf springs) type arrangement for durability.

Kind regards
FollowupID: 372205

Follow Up By: Member - Matt Mu (Perth-WA) - Tuesday, Jun 21, 2005 at 21:50

Tuesday, Jun 21, 2005 at 21:50
Yep absolutley...the integrity of your shockies is paramount. Im running mine with Alko springs which already have the dampener wafers built into them, plus the natural dampening of leaves so Im hoping they will last the test of time. The lower mount is supplied in the kit but the upper mount I made up out of 5mm angle and welded it into a corner of the trailer chassis, I think will suffice for my needs.

This is an offroad trailer but you would be a little unwise to subject it to the Gunbarrel or CSR or the Cape without great care. I hate corrugations!! But in saying that i did snap a spring on a very poor Mereenie loop and all the hangers stayed in place, so maybe testament to the origional construction.

Basically my shocks are 'in-addition' to the origional setup and not a necessity so if a breakage was to occur its a simple fix roadside. The complete kit was only $140 including mounts, so worth the shot in my book and Im VERY impressed with the after-fitment ride!

Goodluck with your trailer!

FollowupID: 372277

Reply By: Member - Beatit (QLD) - Tuesday, Jun 21, 2005 at 13:30

Tuesday, Jun 21, 2005 at 13:30
Thanks for the responses so far, I should also have added that there is limited travel in the springs and that I measured this by jacking up one axle end as high as possible and noting the differenece between the compressed spring on one end and the hanging spring on the other. I figured this would pretty well give me the maximum travel distance for any shock. I'm taking that distance and placing it in the middle of the shockie travel, so that the shock can neither be fully compressed or be forced to hold the weight of the trailer.

Also figure that forward motion would cause mainly an upward/rearward action when the wheel encounters a bump - so figured that the shockie should face the rear of the trailer.

Kind regards
AnswerID: 116711

Reply By: Barnray - Tuesday, Jun 21, 2005 at 20:17

Tuesday, Jun 21, 2005 at 20:17
I think you will find that the angle has more to do with axle travel and the max allowable upward travel of the axle without damaging the shocks by bottoming out. Barnray
AnswerID: 116781

Follow Up By: viz - Tuesday, Jun 21, 2005 at 22:17

Tuesday, Jun 21, 2005 at 22:17
Was just going to say that :)

I have a pair of Koni adjustables on mine - maybe that is a solution, so you can play around with different settings. They would be quite good I think.

May need to experiment a bit more with mine - I think either the springs are too heavy (no give) or the shockies are set too hard. The trailer seems to bounce a little from side to side and do a high frequency weave (damps out after a few cycles) when it hits a bump...

FollowupID: 372282

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