Let's talk about up travel. What is it? When do we use it? Why does it matter? How do we preserve it? Do we want more of it?
Up-travel: What's the big deal?
- Thread starter jjvw
- Start date
Maybe we can start by imagining a Wrangler that has lets say 5" of down-travel and 1" of up-travel. Picture that in your head.
You can droop the hell out of the wheels / axle, but what about on uneven terrain when the opposite wheel wants to go up, while the other is going down.
If it doesn't go up on one side, you're going to be leaning at such an angle that at some point you may actually roll over.
You can droop the hell out of the wheels / axle, but what about on uneven terrain when the opposite wheel wants to go up, while the other is going down.
If it doesn't go up on one side, you're going to be leaning at such an angle that at some point you may actually roll over.
OP
If the body doesn't stop the wheel from traveling up first (let's hope it doesn't), the up-travel will hopefully be stopped by the bump stop. If no bump stop is in place, it's going to be stopped by the shock itself bottoming out, or something like the track bar / axle binding up on something else.
OP
Once the limit of travel is reached, let's assume via the bump stop, the wheel is now pushing the body up.
Yes, assuming there is enough force (i.e. an obstacle) to continue pushing the wheel (and therefore body) up.
This is why I had mentioned that at some point you risk tipping the Jeep over on its side.
Hopefully my thought process here is correct.
This is why I had mentioned that at some point you risk tipping the Jeep over on its side.
Hopefully my thought process here is correct.
OP
Correct. Eventually, the rising wheel is also pushing the body over causing it to lean. A leaning body can create instability. Think about that with regard to LCoG builds.
Now, think about the turning into the the grocery store parking lot. How does this off road stuff apply on a daily driver?
With the LCoG builds, it seems to me (and maybe I'm wrong?) that you're going to potentially have more issues with the rising wheel pushing the body over easier.
I'm not entirely sure about a daily driver. I can tell you that after the mid-arm lift, mine has a lot more body roll when turning corners (though in all fairness, I have no rear sway bar... yet). If I were to hit a corner hard enough, I'm pretty confident I could fairly easily lift one of the wheels off the ground.
OP
The changes from the mid arm and no rear sway bar are a bit of distraction. Those are more related to the control of movement, as is the shock valving.
OP
Speed bumps, pot holes, dips on the highway, entrance aprons, washboards, dips and woops all benefit from suspension up travel. Give the wheels somewhere to go before they start shoving the body (and you) up and out of the way.
We should take the body out of the equation. That is solved by different fenders, torches, sawzalls, and jig saws. After that, we have the chassis which has one end of the shock mounted to it and the axle has the other end.
As you know, it is all about the time to do work. If want to save something from damage, the longer you can delay full impact, the less likely there is to be damage (or in this case, harshness). The longer we can give the shock to do its work of damping road surface events, the less harsh they will be. If we restrict the time (travel) then we have to increase something to slow down the impact and that something is how much damping the shock has. The less time it has to do work, the greater the resistance to movement has to be. In short terms, the less time it has to work, the higher the damping has to be to get the job done.
As for the rest. A rig with 2" of up travel will start moving the chassis upwards on a slightly higher than 2" tall rock on one corner. A rig with 6" of up on the same corner won't even transmit to the driver that he ran over the same rock.
If you do the same type test at higher and higher speeds. 5 mph, 10 mph, 15 mph, and so on, as they increase, the harshness level into the cab increases at a very high rate. The shock simply doesn't have enough time to do its job and we pay for that with low performance, increased risk of damage, and just outright discomfort.
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It is not that difficult. It is just without some attention paid and possibly some alterations, that 50/50 split isn't really enough to let a shock do its job.
In perspective, 9"ish travel shocks with 4.5"ish up and down are pretty common on the back of mildly lifted TJ's.
We pay a lot of attention to the "Would you rather" type scenarios when we are building stuff. One of our common questions we continually challenge is "would you rather have the mid arm or a proper shock outboarding with tuned shocks and a well done short arm. If the answer is one and only one, it is the shock work. Nothing else you can do will affect ride quality or performance in a positive way as significantly as a good shock job. Nothing.
OP
In the world of off the shelf shocks, like the commonly recommended Rancho rs5000x, do the manufacturers assume a ~50/50 travel split for their valving? There must also be an assumption on the vehicle weights that we could pay attention to and utilize. I'm thinking about ways people can better select shocks outside of the regular blanket Rancho or Bilstein recommendations.
Was thinking the exact same question. Is a 50/50 split the "go to?" for shock makers?
OP
A travel distance for the ratio may also be an important detail. I bring up the factory 4" often as a minimum benchmark to maintain. But I do that mostly to encourage people to pay attention to what they are doing. It's clearly more complex than that, since most comfortable cars on the road have less suspension travel than a TJ.
