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  #1  
Old 05-18-2004, 04:19 AM
Chuck K. Chuck K. is offline
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I give, what does "unloading" mean?

I must be the only one who does not know the meaning of this term is. I have read the context surronding it and still don't have a clue.. The post topic was around a FT 6" LA "unloading" while climbing a hill If someone could explain this I would really appreciate it.. Please dont use a lot of "them big words" so I dont have to get out the "hard word explainer" (dictionary)

Thanks, Chuck
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Old 05-18-2004, 05:13 AM
Tumbleweed Tumbleweed is offline
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Here is how I think of it in simple terms. Imagine taking the coil spring out of a ball point pen. Put it between two fingers and compress it some. Now, snap your fingers open and watch the spring "unload". Okay, now think of your coil springs doing the same thing.

Note: I am sure someone here can come up with a better explanation, I am terrible about relaying my thoughts into readable english.
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Old 05-18-2004, 05:46 AM
Chuck K. Chuck K. is offline
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Thanks I get the general idea, but how is this a problem with LA kits while climbing? Is this not a issue with SA lifts? Chuck
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Old 05-18-2004, 07:07 AM
mrblaine mrblaine is offline
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Don is correct in that is what the spring does.

Why it does it is related to gravity and angular weight shifts or weight transfer.

In order to aid with the visualization, I'm will use the two extremes, parallel to the ground and vertical.

At parallel to the ground, the weight of the rig is shared by all four springs. They are loaded with their respective portions of the rigs weight. As you raise the front of the rig to vertical, none of the springs are carrying any weight and are now unloaded.

At various angles in between those two extremes, the weight will shift back and forth, typically to the rear as we spend more time climbing than we do descending. In either case, at something just less than vertical with the rear tires on the ground, the front will have unloaded completely and allowed the front springs to extend fully, or carrying no load and the rear is carrying all the load.

When someone talks about unloading in reference to a rig, what they generally mean is that the rig's nose was up at enough angle that the springs extended because of the weight transfer to the rear axle.

There are several ways to combat this, competitors run a cable to the center of the front and rear axles to allow them to tension the cable and limit how far the springs can extend and change the attitude of the rig.

The downside to that is that you are limiting the effectiveness of your suspension.

The better way is to build your shocks to compress easily and extend slowly. All of which is negated if you spend any time at all with the nose up. Works really well if you are capable of getting lined up and just driving up something and letting the rig's suspension work.
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Old 05-18-2004, 08:14 AM
Chuck K. Chuck K. is offline
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Thanks alot Blaine for taking the time to explain this to me in such good detail and in a manner I could understand. Just one last question (I promise) is what is the penalty while climbing a hill and having the springs become "unloaded"? If you explained this in the above statement I apoligize for not fully understanding it.. Thanks again for the patience... Chuck
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Old 05-18-2004, 08:31 AM
mrblaine mrblaine is offline
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Quote:
Originally posted by Chuck K.
Thanks alot Blaine for taking the time to explain this to me in such good detail and in a manner I could understand. Just one last question (I promise) is what is the penalty while climbing a hill and having the springs become "unloaded"? If you explained this in the above statement I apoligize for not fully understanding it.. Thanks again for the patience... Chuck
Typically it's loss of traction on the front axle and forcing the rear to do all of the work. Another issue is that when the rear springs take all or most of the weight, the ride height changes dramatically and in doing so, changes the arm angles affecting your anti-squat values or ability for the rear to maintain traction.

What was once a well behaved suspension now does bizarre things. The worst would be pushing the front end of the rear arms downward and as the rear axle attempts to propel the rig forward, it instead pushes the body downwards, which in turn lifts the front higher and that loads the rear more which pushes the arms lower in the front, endless cycle which makes climbing difficult.

Ideally, in my mind, you would like the arms to be slightly above parallel as the rear loads so that they attempt to push the body slightly upwards, forcing the nose slightly downwards and maintaining some front traction.

There are a host of terms like Cog, anti-squat, squat, None of which I understand well enough to debate with anyone, but I have an intuitive understanding of what I would like suspension to do, I can see all the forces at work in my mind, I just can't explain them very well. There are also formulas, spreadsheets, and chassis/suspension books out there to help educate we the unknowing.
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Old 05-18-2004, 08:59 AM
Chuck K. Chuck K. is offline
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Quote:
What was once a well behaved suspension now does bizarre things. The worst would be pushing the front end of the rear arms downward and as the rear axle attempts to propel the rig forward, it instead pushes the body downwards, which in turn lifts the front higher and that loads the rear more which pushes the arms lower in the front, endless cycle which makes climbing difficult
Ahhhh... I am getting the big picture now... No pressure on the front end makes for little traction/help going up a hill. Does the above statement cause the dreaded "hop" where a rig begins a violent cycle of gripping lunging forward and up almost to the point of being air born and back down, that sometimes results in breakage?
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Old 05-18-2004, 10:24 AM
mrblaine mrblaine is offline
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Quote:
Originally posted by Chuck K.
Ahhhh... I am getting the big picture now... No pressure on the front end makes for little traction/help going up a hill. Does the above statement cause the dreaded "hop" where a rig begins a violent cycle of gripping lunging forward and up almost to the point of being air born and back down, that sometimes results in breakage?
It can contribute, but there are so many variables involved that's it's hard to pin hopping down to one only.

Shock valving, tire pressure, arm angles, and sometimes just simply the terrain. I do know with mine I can put it on an angle and start the tires slipping, ease into the throttle to heat them up and it never hops. Ease out of the throttle to where the tires just stop spinning and ease back into it and walk right on up.
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