[pete_79]

Can the brains trust please help me with a little explanation on the variables in shocks?

Specifically I’m wondering what are the differences between front and rear shocks.
Is one more resistant to fade on long periods of corrugations then the other?

I ask because I’m messing around with an idea for triangulated 4 link and airbags under a camper trailer.
Airbags are very reliant on the shocks and I’m at the point where I need to make a call on which way to go with these.
I have a couple of different sets of standard front and rear shocks off different vehicles here. I’m leaning towards the brand new ones out of a modern hilux and I’d like to use what I have at hand for now.
If I feel I need to upgrade in the future I can just get an after market set to replace the stock ones.

I guess I’m just looking for a better technical understanding of the design differences between front and rear shocks.

[Gwagensteve]

None. There are no inherent differences in design between front and rear shocks. They all just turn motion into heat.

The variables are length, mount configuration and valving.


Valving will vary substantially between a shock designed for a leaf sprung axle (which will have light valving and) and an IFS front end where there is little or no inherent friction in the suspension and the shocks typically travel less than the wheel motion. This means they require quite stiff valving to control the wheels and maintain traction.

Your best bet is to use a “universal” shock that is available in a range of valving like a Bilstein 5125

There are a number of different construction methods for shocks but these vary between manufacturer and budget, not location. The most resistant to fade are remote reservoir shocks which have the largest oil volume by design, but are consequently the most expensive to purchase.

Bear in mind though that because a trailer is undriven, most of the design parameters for a shock (or suspension design) aren’t relevant. It’s also why most trailers have simple swing arm suspension- a 4 link is better for managing drive/braking load, but that’s irrelevant, likewise, the suspension doesn’t have to maintain traction, only prevent excessive sway and bouncing.

[pete_79]

Thanks Steve.

So I should probably be looking more at the front shocks from the Hilux and consider replacing with remote reservoir units if I feel it’s needed.

Re the 4 link;
I’ve discarded things like the anti-squat and pinion angle, but have tried to put the instant centre right on the hitch and kept the roll centre as low as possible.
The airbags have 100mm of travel, so I’ve designed everything riding at mid travel. I believe drop in more important on a trailer to keep the wheels on the ground. The hitch takes care of flex.
The 4 link on the trailer is just an exercise for me to mess around with something different. So far it’s cost me under $100 for the bushes and tube.
I just wanted to play with the design and fabrication to see if I can make it all work.
If I totally stuff it all up and it doesn’t work out there’s a set of leaf springs sitting here ready to go in.

I’ll dig all of the front shocks out of the box and see what I think.

Thanks again mate.

[Gwagensteve]

Instant centre isn’t relevant either IMHO as that only applies to torque being applied to the axle. A simple parallel setup would work fine.

[pete_79]

Yeah I’m really tight between the chassis and the body with my width tyre.
Hoping the 4 link gives more controlled travel then the radius arc from a panhard and parallel 4 link or using some version of stock radius arms.

Like I said this is just an exercise in ‘can I do it’.
I figure it’s much easier to mess around on a trailer that I am making a new chassis for, then to go and hack apart a vehicle only to realize I may have over estimated my capabilities....

[Gwagensteve]

Ah- that’s a roll centre issue, and under those circumstances it’s easiest to build a high roll centre with a triangulated 4 link or an A frame three link, which will pull your tyre away from the tub as it flexes. (Not that trailers really flex)