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Good design vs bad design
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I thought the whole point of the video(s) was a “cheap Jeep challenge”.
I think they both tried to keep it around 5k all in. With that said, I can certainly forgive some shortcuts and less-than-ideal suspension geometry. With regard to what their goal was; I’d say they both succeeded.
I think they both tried to keep it around 5k all in. With that said, I can certainly forgive some shortcuts and less-than-ideal suspension geometry. With regard to what their goal was; I’d say they both succeeded.
What are the qualities of good suspension geometry? What is happening in the rear that causes the front to behave that way? Why does the geometry matter so much in a situation like this climb, instead of just the wheelbase and center of mass?
I'm fuzzy on the specific behaviors of leafs, except that I see what I believe to be what looks like low antisquat. During a steep climb this will cause the rear to sink under drivetrain load. The weight shift from this sinking rear will make the front end lift. With linked suspension, the amount of antisquat can be tuned by moving the control arm mount locations.
The two extremes we usually see of bad suspension geometry on a steep climb are the sinking rear/light front described above usually from a lifted long arm, and a rising rear that leads to an uncontrollable hopping usually seen with lifted short arms. A preferable behavior is somewhere in the middle, where the rear doesn't sink or rise when under load. This is what we see in the Ultra 4 car that greatly contributes to it's stability and smoothness.
We went wheeling with a YJ last weekend on leafs and it was excruciating to watch. At first I thought the guy was just a really bad, throttle heavy driver, but then I was told that with leaf springs you have to come into an obstacle with more momentum than you would on a TJ (not sure if that's true or not?) due to the suspension not wanting to articulate with leaf springs as easy as it would with coil springs.
Anyways, it was painful to watch and ultimately ended in the YJ running into a large rock and snapping the motor mount, which then ended up smashing the oil filter into the rock and spilling oil everywhere.
My dad and I have discussed this somewhat. When he was building his cj5 in the 80s-90s, he paid a lot of attention to the leafs to make sure they were just enough to create the ride height without creating too thick of a leaf pack. This meant his CJ was often far more flexy than others allowing him to approach obstacles more slowly and carefully. Consequently, his softer leafs eventually led to axle wrap and a broken pinon.
Line choice and a better driver. While not apples to apples; leafs, even when under the axle (spring under) can take on Johnson valley.
A smart driver with the right experience/seat time can make something that every other driver struggle with, look easy to crawl.
Remember even at The King of the Hammers this year, Jesse Haines race rig was on leaf springs on all four corners and sprung under the axle....he won the stock class and finished 19th overall at KOH after starting 122nd. Im sure most would look at that rig and say its a legacy setup and wouldnt bet money on it winning.
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Your Dad was right on the mark with the idea of a progressive rate spring and more thin leafs...Honestly over the years it’s shown that the aftermarket is more in tune to manufacture the right progressive rate spring for off road type vehicles.
As I understand it, a factory vehicle is built to go 200k miles down the highway and that’s about it.
The Deaver spring’d raptor was a killer at the Baja 1000 when in pre production w/ Ford. The Ford guys were very impressed with what Deaver could do to a leaf. The second gen raptor followed in the foot steps of Deaver and manufactured a clone spring bc it was such a better spring.
Some of the late model Tacomas had a negative arc’d spring from the factory. Resulting in broken leafs and a TSB being released.
Is there better deisgn? Yes; links and coils, in almost every sense. They are far superior design for what we all want and like to do. They just plain work almost beyond what we, as everyday drivers are capable of.
The antisquat is determined by the instant center. Understand how and why that is and you will be further along than most.Thanks, that makes more sense. Time to read up on antisquat
You are correct on the behavior of the leaf springs. Their anti squat does vary by arch, use of blocks, shackle length as well as mounting location just like links but it is typically on lower side. Then you add in they are running a radius arm on the XJ which allows the front to unload the moment the Jeep goes vertical and you get the results shown.
ZJs are doomed from the start and will have horrible control arm angles the moment you want to fit any decent size tire on them. I guarantee there will be plenty of people commenting on the vid that they need a long arm of course.
I'm not convinced that radius arms have anything to do with the unloading. There is no front arm design that can control what the front is going to do. All one can do is try to control the weight shift by controlling how the rear behaves.
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