Determining spring load for roof rack.

[OFC Ranger]

While I have not run into any problems yet, a small upgrade I want to perform on my rack is moving away from static tension set leveling feet for the portion that spans over the roof of my truck. The simplest way I can think to allow for dynamic movement is adding a spring between the bottom nut and the bottom of the rack.

Where I don't know to start is determining a tension rate. I want it to be strong enough to act as static support, but allow very slight movement upward, but still make solid contact. I am guessing however that a small miscalculation and I will get "bounce" if the movement is sudden enough, ie; the feet will lose contact (even if only a split second) with the roof channels.

I have attached an older picture, but should give you a rough idea of what I am after. Honestly I am not even sure if his is going to be possible.

The next idea is mounting a hard point (ball joint) in the roof channel and utilizing a proper strength gas strut (commonly use for campers, cabinets, etc etc). The trick here is mounting it so its not fully compressed, or fully extended and its normal position is floating somewhere between the two. I'm thinking an 80lb strut or somewhere in that area is what I would be after.

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[D Fresh]

Just a thought.

If it were me I'd want to stay completely away from touching the cab. Especially if I were purchasing a rack, which I believe you are looking at selling.

I'm no engineer, but could a short vertical support on each side at the center support suspension cables to the front and rear corners?

Not sure if it could be done small and strong enough.

 

[OFC Ranger]

While I would not want a hard static mount due to body flex between cab and bed, I'm not sure why people shy away from full length lighter weight systems other than production cost reasons. I mean the easy answer is just run ten feet framing using thick steel, but weight is the trade off. However this is why I use the roof channels and not the roof for the contact point and why I use rubber feet (squish/flex).

While I have been approached about selling a DIY kit on a few occasions now, as of now this build is just for private use. So the good news is I can get wacky with the ideas. I am a big fan of over-engineering and unorthodox construction if for nothing more than the thrill of building something custom. On the plus side if the design actually functions like its suppose to, it moves more into the premium custom category and I don't have to worry as much about other people ripping my design off because it will be seen as "not practical". Pffft.

I considered a suspension system using eye bolts and steel cabling (set up in an X pattern under the platform) it just didn't come off in my head as being as sturdy or as nice looking.

Edit: Also if I can figure out a multi-position gas strut setup I can move to a single POC on each side instead of multiple feet. Also, I think it will have a pretty nice industrial look for the overall package.

 

[OFC Ranger]

Huh... so cruising around Google for ideas an info I think I may have stumbled across a third option.

It sounds silly, but a bicycle shock absorber. This actually looks like it may be more suited to my idea than a strut... hmm... might be too strong. I wonder the weakest on the market.

 

[Travism]

While I have not run into any problems yet, a small upgrade I want to perform on my rack is moving away from static tension set leveling feet for the portion that spans over the roof of my truck. The simplest way I can think to allow for dynamic movement is adding a spring between the bottom nut and the bottom of the rack.

Where I don't know to start is determining a tension rate. I want it to be strong enough to act as static support, but allow very slight movement upward, but still make solid contact. I am guessing however that a small miscalculation and I will get "bounce" if the movement is sudden enough, ie; the feet will lose contact (even if only a split second) with the roof channels.

I have attached an older picture, but should give you a rough idea of what I am after. Honestly I am not even sure if his is going to be possible.

The next idea is mounting a hard point (ball joint) in the roof channel and utilizing a proper strength gas strut (commonly use for campers, cabinets, etc etc). The trick here is mounting it so its not fully compressed, or fully extended and its normal position is floating somewhere between the two. I'm thinking an 80lb strut or somewhere in that area is what I would be after.

Did you ever figure out this rack issue? I built my own and am now going to the spring idea, but the shock idea is more ideal. How did the compression springs work?

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