Quote:
Originally posted by mrblaine
The reason that coils are more of a problem when you remove their normal load from them is that they have more travel typically and can dramatically shift your CoG.
Unloading is simply that. Remove load, spring gets taller, add load spring gets shorter.
At anything other than parallel to the ground on a flat surface, no spring is carrying it's normal share of the load. The load will be distributed according to the variations in the surface the tires are sitting on.
The greater the difference in heights, the more load an individual spring has to carry.
Coil link suspensions will attempy to balance until they run out of travel in either direction. Diagonally, if two springs are fully compressed and the other two are fully drooped, the total weight of the rig is being supported by two springs.
Same thing happens front to rear. The nearer to 90 degrees you get the frame with the front higher, the more load is carried by the rear springs until such a point that the entire weight is compressing the rear springs. That means the fronts are fully extended and carrying no portion of the vehicle's weight or unloaded.
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I understand now. Whether it is the leafs or the coils, what you are all referencing is not so much the actual act of 'unloading', or the release of energy, but the change of apparent CoG, at times on very steep inclines, the CoG apparent is actually behind the Jeep a few feet or more.
Ah, yes, the bane of short wheelbased vehicles approaching vertical.
This is an age old problem but dynamics suggest the coil will be more prone to this than a leaf, since the leaf has two ends still attached physically to the Jeep at each spring, thus, still has 8 point contacts with the Jeep.
The converse, the coil, has none, it attaches to nothing and therefore when the excessive articulation occurs as the vehicle nears vertical, the axle is literally laying there. And that is the term you are using for 'unloading'. And as Jeeper pointed out, the control arms are still taking some of this stress-unloading transfer to the rear.
I understand now.
Engineering wise, I've discovered the first weakness in my hero of all Jeeps, the TJ marque, by this discussion. I'll be damned--I never thought of the lose, unattached coil spring as the means of transferring to weight to wheel, via unloading on vertical. And this is the issue with your TJs in climbing those vertical escarpments. The leaf is prone to this too, but far less so. How intriguing.
My compensation for this was always to put more weight, one way or another, over the front.
Thanks for all your timely and exahustive documentation on this. Too, for one never having a TJ and not Jeeping around them with the same application as VEX, this is new to me and now understood. I've never had a coiled spring equipped
anything, ever........
I also now see the need for the limiting straps, the tiny winches sucking the axle and frame together, etc. It is the coils. Obviously. A quarter eliptic leaf would do the same in part, to a lesser degree.
Everything is a trade-off in applied dynamic.
What a cool learning curve..............