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Some will say that an extreme drooped tire has a stabilizing effect. For that to be true it has to have weight on it or it's simply just touching the ground.
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I Don't think this is completely correct. Having weight on it certainly makes it of more use, but is not essential for it to help out. Even if it is just touching, you still have the stabilization of the shock rate resistance to shifting. The only real problem with "lifting a wheel" is that it destabilizes the truck by allowing it to fall off on that side if the CG shifts over the balance point in that direction. In that case, there is nothing (significant) other than inertia acting to limit the vehicles movement, so you get a violent shift till the tire touches, then the shock has to deal with the inertia resulting from the uncontrolled fall, and the result is that the vehicle goes quiet a bit further "over" that direction than it would have if the shock had controlled the shift, and the result is often a roll or flop. So, all other things being equal, I would rather keep that tire touching the ground than in the air where it (well, the shock) can't help control shifts in that direction. Even if it's not touching the ground, if it makes contact 2" sooner, then that's 2" of falling that does not lead to more inertia that must be countered, and the result is that the truck does not go as far in that direction before rebounding to find equilibrium.
That's the viewpoint of weight shifting onto a tire that's in the air vs. touching (or at least closer to touching) the ground. But what about on the up hill side? If the tire is free to drop away some distance before you start getting resistance (effectively transferring un-sprung weight back into the chassis on that corner) then this can be a problem. In fact, it's a common argument FOR leafs vs. coils and especially coil-overs. What happens is that once leafs go past their natural arch (that you see with them lying on the ground) they start to resist further travel. This not only helps control body roll, it lets the unsprung weigh on that corner be used like a counter weight to help keep you from going over. The further that side can droop, the further over you will go before a comparable amount of weight is added to that corner, and the less likely it is to be "enough" (since the chassis if further over the balance axis). So, leafs apply steadily increasing resistance to that droop as they move further into droop. Coils can also help some here if they are "restrained", but will typically apply resistance in a linear fashion. And coil-overs typically just keep pushing the tire away (multi-stage coils will reduce the amount of push as it extends, but it's still pushing) till the shock tops out. Enter the sway bars… Use of a sway bar will not only help prevent/reduce body roll (which is a weight/mass/inertia result), but it will also help transfer un-sprung weight to the chassis on the drooped corner.
Of course, applying the points in the second case to the first case above, this means that it's going to tip to the down hill side sooner! <grin> Lots to think about, and it can't be summed up in a few simple anecdotes or a one line "rule of thumb". The only "one liner" or "simple rule" I can think of that ever applies to suspensions of any kind is that "It is all about compromise and finding the compromise that best suits your needs." Of course to make use of that, you need to THOROUGHLY understand the results and trade-offs of each input variable to make an intelligent decision and get the best results. Designing for optimum performance in more than one area (crawling AND high speed) means many more trade-offs and you need to be even more aware of the details. And it means that a single post like this is not going to provide you much benefit without countless hours of additional reading and research on your part. This just barely gets you started. You need to be able to quantify all these interactions and figure out what that means to your final vision/need before you can make a decision.
Many say, "Don't over think it, just do it!" But frankly, that's silly in the extreme if you really want it "right" and you want that the first time (allowing for a few tweaks that are inevitable). It's quite likely that with a reasonable amount of research you can come up with something that works. And it's not unlikely that you will come up with something that works better than what you have now, especially since most people focus on the "big things" they want and can zero in on a design that addresses those points relatively easily. And they often (incorrectly) reach the naive conclusion that you don't need to learn, research, and know the details. However, all they've really shown is that, "you don't need to do all that work to do better than what you had for the desired purpose". And of course many of the "just do it" crowd wind up with dismal failures where the vehicle will literally flop itself on level ground when you hit the accelerator!
Then again, it may be useful to look at the other side of the coin where you will find something known as "analysis paralysis". That's where I seem to find myself ever time I start looking at my truggy now. Buggy vs. Truggy. Torque tube, vs. 3-link, vs. inverted-reversed 4 link, vs. double triangulated 4 link, vs… I find myself unable to accept the compromises that fall out of any of these designs when applied to my current truggy, which leads me to thinking of a buggy, and realizing I don't have the time, patience, knowledge, or resources right now to build a buggy. Net result: nothing gets done…
As for comments on unclamping the leafs and "controllable travel", I would sorta disagree. I do agree that "the quest for travel" is often WAY overdone by novices and enthusiasts alike. However, I'm not sure exactly what the definition of "controllable travel" means. If you're talking about lateral control of the axle being lost, or excessive axle wrap and waking under (like 3/4 ellips do on the front) because the suspension has gone beyond its design limits, then we agree 100%. But I prefer to think of it as "the compromises exceeded the benefits and net performance suffered a loss". In other words, it's really not "uncontrollable", it's that the "cost outweighed the benefits. On the unclamping leafs, it seems to me that, other than longevity of the springs, there is no reason that this should not be considered. Not necessarily done, but considered. You just have to be aware of the resulting effects, like those expressed in my first 2 paragraphs.
I guess I should stop now. I have more thoughts on this matter, many more actually, but I'm getting tired of typing, and I expect only about half of those reading this will even make it to this point, so I'll call that enough for now…
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Russ
K30 Truggy, 350 TBI, Th350, Doubler, D60/C14, 4.56 Locked, 4" lift, 42" TSLs, 112" WB, almost 90* approach and departure angles.
