Flat Deck Design Considerations

#1
We have just purchased a 2010 FG 140 as a Cab & Chassis. I just wire brushed the chassis and painted it with por 15. We plan to install a flat deck and use the truck adding a camper in the future. As I have not decided the type of camper we will add so my primary objective now is maximum flexibility. I have been talking to local builders, who build service trucks for the logging industry, and have included their recommendations.
I would appreciate any feedback on the design considerations and any I have not considered.
  • Steel VS Aluminum: flexibility vs weight (steel recommended)
  • Solid Mount or Spring Mount: I do not intend to do heavy off road mostly logging/gravel roads (solid recommended)
  • Stepped Deck VS No Step: hight versus flexibility
  • Width 7’ vs 8’ Camper size versus drivability.
  • Cushion/bushing between chassis and flat deck polyurethane versus wood
  • Steps for future camper: Hard to add later. Pre determines door placement. Could provide access to deck when camper is not installed
Thank you for your input.
Chassis.jpg
 

pugslyyy

Robinson Fuso
#2
Welcome to the forums. There's a pretty larger body of experience and knowledge here that you should research and take advantage of. What is your target weight, and will you be doing a SRW conversion?
 

SkiFreak

Expedition Leader
#3
I would appreciate any feedback on the design considerations and any I have not considered.
As Plugslyyy has already stated... have a search of this forum, as many of your questions have already been discussed, at length.

As you have eluded to, the step placement will definitely play a determining factor on the camper design, so your modification plans should probably include designing the camper body and its basic layout along with designing the tray.
Something to consider is that if you will be building a slide-on camper, the camper floor height will be fairly significant. Should you be adding singles, which are normally of a larger diameter, along with any updated suspension, your floor height will be even higher. To that end, whatever steps you go with, they will probably have to be fairly substantial if they are to have any decent stability.

The step in the FG frame affords a possible design oportunity in regards to designing/building a retractable camper step solution. The steps can be on rails that are easily slid out when necessary. A side benefit is that they could also be used to easily access the tray.

If you do research the solid/flexible mounting further on this forum, you will find that I am strongly biased towards spring mounts. I make no apologies for that, as I strongly believe it to be the best mounting system for an FG.
Something that is continually overlooked by people doing custom builds on Fuso FG trucks is that they are not like other trucks. Unless a business fully understands this specific model of truck, I would take their advice with a grain of salt.
As I have stated many times before when discussing this topic, reinventing the wheel seems pointless to me. Here in Australia we have a very large market share of the Isuzu and Fuso 6 tonne 4x4 trucks, as they are used extensively as Rural Fire Service vehicles around the entire country. With very few exceptions, these trucks are built with some form of spring mounts between the chassis and tray/subframe. There has to be a reason for that.

I'll get off my soap box now...
 
#4
As Plugslyyy has already stated... have a search of this forum, as many of your questions have already been discussed, at length.
I'll get off my soap box now...
You are entirely right.
You need to be careful you don't slip of that soap box if it gets wet.

Dan.
 
#5
Thank you Pugslyyy (my cats name lol). I have been spending a lot of time digging through the forum and am trying to shape the direction I will take. I will likely do a SRW conversion but am holding off until I have a better understanding of the options. My understanding of my options in Canada so are:
http://www.trucksupersingles.com.au/index.html or http://allterrainwarriors.com/accessories/
It seems like this decision is very closely related to you second comment about target weight. I am so new to this process that I don't have a number in mind. I am coming to this with a background in Autobody and Woodworking the Heavy Truck world is very new to me.
Thank you for your input.
 
#6
As Plugslyyy has already stated... have a search of this forum, as many of your questions have already been discussed, at length.
Hi SkiFreak, I appreciate your feedback I have spent quite a bit of time reviewing the form and your website. I do admit to feeling a bit of information overload.
As you have eluded to, the step placement will definitely play a determining factor on the camper design, so your modification plans should probably include designing the camper body and its basic layout along with designing the tray.
Something to consider is that if you will be building a slide-on camper, the camper floor height will be fairly significant. Should you be adding singles, which are normally of a larger diameter, along with any updated suspension, your floor height will be even higher. To that end, whatever steps you go with, they will probably have to be fairly substantial if they are to have any decent stability.
Wanting the door of a future camper on the right if I am going to have a step it will have to be placed between the tank and the rear wheels. You have hit my my primary question regarding steps. Without the camper design and the final ride hight determined is it foolish to prebuild steps? Perhaps but the rise and run will also be set by the available space. This is something I am going to have to work through.
The step in the FG frame affords a possible design oportunity in regards to designing/building a retractable camper step solution. The steps can be on rails that are easily slid out when necessary. A side benefit is that they could also be used to easily access the tray.
I like this suggestion but am not sure I fully understand. Are you suggesting he stairs would be on rails sliding in from the rear of the truck?
If you do research the solid/flexible mounting further on this forum, you will find that I am strongly biased towards spring mounts. I make no apologies for that, as I strongly believe it to be the best mounting system for an FG.
Something that is continually overlooked by people doing custom builds on Fuso FG trucks is that they are not like other trucks. Unless a business fully understands this specific model of truck, I would take their advice with a grain of salt.
As I have stated many times before when discussing this topic, reinventing the wheel seems pointless to me. Here in Australia we have a very large market share of the Isuzu and Fuso 6 tonne 4x4 trucks, as they are used extensively as Rural Fire Service vehicles around the entire country. With very few exceptions, these trucks are built with some form of spring mounts between the chassis and tray/subframe. There has to be a reason for that.

I'll get off my soap box now...
I have spent a great deal of time reading your posts on http://canter4x4.com and find the photos extremely helpful. I a a firm believer in borrow from the best learn from the worst. I am wondering about the details of the springs you used? Did I somehow miss that?

Thank you again for your input.
 

SkiFreak

Expedition Leader
#7
I a a firm believer in borrow from the best learn from the worst.
I often question where on that scale I fall... ;)

Regarding the steps...
They say a picture is worth a thousand words, so we will start with that.
steps_01.jpg
steps_02.jpg

Above is an example of what I believe would work well, but I would have the steps running east/west, not north/south, as the do in these pictures.
If you build a flat tray, which in my opinions if far more practical, you will get a usable void behind the chassis step down. You could build a slide out step mechanism which fitted into that space, as you have at least 2 metres of width to work with.
The design could be as in the above images, or the steps could be longer, so that they reached the ground. My preference would be the latter, as I believe they would end up being more stable that way.
If the steps were long enough to reach the ground, based on the height of the tray.,the two things that would change are the tread height and the angle of the rails. With this type of design, the the treads would always remain horizontal, no matter what the height of the tray is.

I have seen similar variations of this design, where there is a slide out platform and under the platform are the slide out steps.
In that type of design you have very good access and the steps run north/south, so they do not protrude out too wide.
 
#8
If you haven't decided on a camper design yet I personally wouldn't put permanent steps on it anywhere- no matter where you put them they're guaranteed to be wrong... trays are easy to modify.
As to width, imo 7ft is about all you'll want to go. Much more and it just sticks out way too much from the cab. Mine is around 7' and I often wish it were same width as th cab. I do do lots of skinny tracks tho.
Mounting, spring is probably the best bet. Plenty of trucks around that are hard mounted and work fine, inc mine, but it depends what you plan to make the camper body out of. Common nowadays to use composite panels, which I wouldn't put on a hardmounted subframe (for an offroad truck)
My 2c.
 
#9
My five cents definately spring mounted. The chassis will flex.

Why not put a spring mounted frame with container locks on the chassis. That way you can put a flat deck on it for now and a camper body with container locks to slot right on in place later!
 
#11
Bliss Mobil attach the camper to the flat bed that way.
yes I also noticed that and liked that idea. Gives you your truck back for other purposes when the need arises. Simple enough to build a gantry to back the truck under and lift the back off and put the tray back on. Great idea ! Container locks on a frame that is spring mounted. Genius !
 
#12
My five cents definately spring mounted. The chassis will flex.

Why not put a spring mounted frame with container locks on the chassis. That way you can put a flat deck on it for now and a camper body with container locks to slot right on in place later!
Thank you for the input I like the idea of the the container mounts.
 

SkiFreak

Expedition Leader
#14
I am wondering if you have any recommendations on springs for the mounting?
That's right up there with "how long is a piece of string?"
Basically, there is no "one size fits all" solution for mounting a subframe. Many things come into play, like the torsional strength of the subframe itself, the strength and material the camper is made from, the weight of these things and what sort of terrain you plan on traversing, to name just a few.
If you design the mounts in a way that different sized springs could be used, if you get it wrong then simply changing the spring/spring rate could resolve the attachment being too hard or too soft.
After having designed both the subframe and camper, speak with a mechanical engineer if you are unsure about the spring rate you should use, or do like I did and take a "best guess" approach.
 
#15
for spring rate I used some estimate based on box weight (to approximate dynamic forces) with number and location of mounts (2x3 within 2m) and possible chassis twist.

Basically a compromise between keeping the box in contact with the chassis during "normal" use and needing some movement in extreme conditions.

Back to steps for a moment. Probably the most difficult exercise of the design. It occurs to me that with a flat bed the steps have to reach the edge of the flat bed. If they are cantilevered off the side of the flat bed as soon as someone steps on the bottom step from the ground there is moment about the longitudinal axis which anyone inside will feel. Some designs have the top steps within the floor area, others have the bottom step resting on the ground - with some allowance for movement of the vehicle. My scissor steps have a slot arrangement for slide out from between fuel tank and underside of floor - equivalent of flat bed. The end of the slot allows for movement while being deep enough to prevent collapse. Part of steps is to keep the vertical and horizontal distances between steps, including top and bottom, consistent. Even 25mm difference in vertical is very noticeable in use.
 
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