Suspension Options Other Than Parabolic Leaf Springs?

[MSGGrunt]

I am in the early stages of planning my 2005 FG140 build and of course suspension is one of the first modifications, other than super single wheels and tires, that comes to mind. My build will not include a heavy habitat, more likely just a flatbed that I can mount my roof top tent to and use as a flatbed truck when I need to haul stuff. Or maybe a lightweight tarp enclosure like the US LMTVs use or the tarps used on Land Rover Defenders.

Watching this video made me think about the suspension. Seems he is using less leaves in the rear to soften the ride but has the air bags to compensate when heavier loads are carried. Is this not a popular direction to build a rear suspension because most on here are building to haul the weight of a habitat? Steady weight makes calculating spring rates much easier, but this looks like a viable option if heavy weight is not carried all the time, but you have the airbags when you do.



Front suspension? This is where my ideas go a little left of center. Regardless of cost, and because of the inherent ride qualities of a cab over engine design, why have others not swapped to a coil spring set-up like a Ford F550? Lower control arms to keep the axle from twisting and a Panhard bar to locate it left to right. Spring buckets are available or could be custom made along with lower coil seats. A few brackets welded onto the axle and frame for the control arms, Panhard bar and shocks. Seems the ride with coils would be much better. I built up an FZJ80 Landcruiser with this very same suspension design, so that is kind of where I am getting my ideas from.

 

[Czechsix]

Coil springs have been done, but only as a one off build with lots of empirical R&D. Think pre-runner style suspension. Years back I heard he was willing to do suspension builds for folks, but $$ was around 130k.

 

[SkiFreak]

Starting around 2010, All Terrain Warriors here in Australia did a 5 link coil conversions with a Watts link at the rear to about a dozen Canters , of which my truck was one.
I have driven (or been in) numerous different Canters that have had suspension modifications done, but none have really equaled the ride quality of my truck.

 

[MSGGrunt]

I wonder why the radius arms are mounted forward and not rearward like on say a Ford or landcruiser 80 Series? Was it because going forward had more space to mount the arms to the front frame? I was just thinking a radius arm design with Panhard bar would be a simpler design than say a 3, 4 or even a 5-link. Yes, the 3-link is a little bit more limited in how much they can articulate, but that isn't what my Fuso will be built for. I think I would leave the rear on leaf springs, just go with a softer spring rate than stock and coils in the front for better ride quality. Something to think about.

 

[SkiFreak]

The first two trucks ATW converted to coils had leading arms at the front. From what I was told, they had bad bump steer, so the design was changed to trailing arms.
Over the years there were a few other tweaks for this setup, all of which have been made to my truck.

There have been at least two build threads here that have done what you are planning, that being to just replace the front with coils.

The biggest problem with my setup is that it is a bit boat like, due to the linear coil spring setup.
I have considered adding a sway bar, but that's an issue for future me, as I have other things that have a higher priority for now.

 

[MSGGrunt]

Seems like a great place to get any brackets and joints needed.

Link Suspension Parts: Control Arm Brackets, Coil Spring Brackets, Mounting Trackbar Brackets, Rockwell Link Brackets, Suspension Tabs | Barnes 4WD

Suspension accessories are for the customer who wants to build a suspension unique to themselves. From bracketry to total DIY kits. We have something to take your rig to the next level. 3 Link and 4 Link Brackets and TabsBarnes control arm brackets come at the standard 50k tensile strength and...

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[SkiFreak]

As much as I agree that coils in the front are a definite advantage over leaf springs for a COE truck, unless you are skilled in the art of suspension setups, getting all of the geometry correct in a DIY build would be a real challenge.
There is always the option of having a suspension specialist design/build this type of conversion, but going down that route would obviously incur a significant financial cost.
As with many custom builds, the limiting factor is very often money. One off builds are normally not cheap!

 

[MSGGrunt]

I have read where others have used less leaves in the front (3) and back (5) without overload springs and upgraded shocks and bump stops. Mind you, I am not intending to max out the weight carrying ability of the Fuso. Also, some have mention longer springs. It looks like the rear hangers can be cut off (rivets) and moved back a few inches, but more importantly can the fronts as well? I have read that one of the reasons the front rides as rough as it does, besides being a truck designed for carrying its max load and being a COE design, is the shortness of the front springs. I haven't really been under the truck to see what is in the way, if anything, that makes lengthening the front spring more difficult.

 

[SkiFreak]

Lengthening the springs changes the angles of the spring hangars. Being more outward facing means that they absorb shocks more readily.
The standard bump stops are pretty much like solid bricks. Changing these out with something like a Timbren progressive bump stop reduces the jarring significantly.

 

[Peter_n_Margaret]

The first two trucks ATW converted to coils had leading arms at the front. From what I was told, they had bad bump steer, so the design was changed to trailing arms.

I photographed one of those on Fraser Island in 2009. Was it you?

Cheers,
Peter
OKA196 motorhome

 

[SkiFreak]

Was it you?

I don't know whose truck that is. It's not mine.
I got mine in early 2011.

I did not know that ATW did any half and half conversion, as this truck seems to have coils at the front and leafs on the rear.
Maybe they did more than two trucks with leading arms at the front.

 

[Peter_n_Margaret]

My vehicle is an OKA, a unique, Australian made vehicle that was designed and built from the ground up as a high mobility 4WD, rather than a 2WD light truck converted to 4WD as the Japanese vehicles are.
The OKA is a simple design.
One of its features is a leaf spring suspension which is simply superb out of the factory.
The main reason it is so good is because the springs are LONG, longer than any similar vehicle.

It seems to me that if the spring mounts on the vehicle in question could be moved to allow longer springs, there is likely to be a mojor improvement in their performance.
This is relatively easy to do at the rear, more difficult for the front?
Cheers,
Peter
OKA196 motorhome

 

[mog]

Wait until you install your super-singles before you start planning suspension changes. When I swapped from stock wheels/tires to 37/12.5-16s (Falken Wildpeak, NLA? so, 37s on17s now?) it was a world of difference for not only ride quality, but also cab noise as the cruise RPM dropped so much.
You will always be driving a cab-over 'delivery truck', so no matter how much $$$ you throw into the suspension it will not ride like a modern light-duty truck. I think your' budget could be better spent elsewhere before a complicate change to the suspension. That said, once you are at your operation weight (changing before getting to the weight/CG is the cart before the horse) certainly better bump stops, and custom leaf springs for your weight will be an improvement. Search here on the Portal will result in lots of info. Also Ivecos had longer parabolic springs as stock equipment, so perhaps a salvage yard find for the weight cost of 'scrap steel'?

 

[MSGGrunt]

I know this is probably a newbie question that has been asked and answered many times, but 37-13.5-17 tires will fit in the stock wheel openings without have to add new springs with a little lift? I would prefer to wait until the flatbed is built before having custom springs built, but I was just under the assumption that with such a bigger tire I would need new springs to replace the tired and sagged originals and or to lift the truck for tire clearance.

 

[Ultimark]

Unless I am very much mistaken, that Fuso in the clip, is running a parabolic leaf suspension set-up on the front.

Mick.