That's a topic for a different thread. One thing at a time!
Someone should bring that up in the Long Arms vs Short Arms discussion.
Does control arm bushing composition affect ride quality or NVH?
- Thread starter bobthetj03
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That's a topic for a different thread. One thing at a time!
Someone should bring that up in the Long Arms vs Short Arms discussion.
Anecdotally, we both replaced loose worn bushings with new tighter bushings and experienced improvements in NVH and handling. Interesting.
I keep thinking about that shaker table and the track bars.
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There are big differences in the elasticity of bushing materials. Check this out: https://www.acrotechinc.com/shape-factor-modulus-of-elasticity/
If you follow the math, both the shape of the bushing and the elasticity of the compound make substantial impacts on the elasticity of the piece. Consider what cutting holes in a bushing would do to the shape factor in these calculations.
Also, PU comes in a wider range of hardness than rubber, e.g.
Where I'm stuck in this discussion is I don't know where we'd find hard data on what actually goes into the retail bushings we can get for TJs. We could be getting cheap hard crap that does nothing more than fill the gaps between components. Or we could get properly engineered bushings that reduce NVH.
My guess is that someone thought about what went into the OEM bushings. Not sure that's true about all the aftermarket stuff though.
Despite most long arm suspension advertisement claims, with everything else being equal and the same, there's no difference in ride quality between a short vs. long arm at suspension lift heights typically installed onto our TJs. Really.
This is just me thinking and maybe creating a false equivalence through impercise vagueries. For a generic CA joint or bushing to have an acceptable longevity, it needs to be within some range of "soft enough" but not "too hard". In the grand scheme of elasticities and durometers, this range seems like it would be fairly narrow. Meaning that the differences between a softer rubber bushing and a harder polyurethane race aren't terribly far apart from each other.
Consider this along with the observations that simply having a snug connection results in a reduction in NVH compared to a loose connection and it further calls into question that a particular joint or bushing will have a meaningful effect in the transmission of NVH into the frame.
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I also wonder how much different one joint is to another in terms of transmission as most of the motion of the suspension will be around the bolt. For instance in a tj if a bump comes into the front the control arm wants to rotate up. However in an ifs car with a arms the bushings are mounted longitudinally and so the impact goes straight back into the frame without as much rotation to absorb it. Would this be why the tuner market sees a greater impact from bushing material?
I've never run heims, and if I didn't hate replacing them so often I'd be tempted to try. But I'm betting they are the only ones that will be significantly different.
—
There must have been a time
when we could have said no.
I've never run heims, and if I didn't hate replacing them so often I'd be tempted to try. But I'm betting they are the only ones that will be significantly different.
—
There must have been a time
when we could have said no.
Here is my experience take it for what its worth.
When I bought my TJ the stock arms were wore out. It had about 179K miles on it with what I believe were the stock control arms. I promptly changed them for new Crowns. I honestly didn't feel much if any difference. Then a few months later, I installed Currie control arms, and I could feel a ton of difference. To me the best way I could describe it was it went from driving a car to a truck. I could feel the road a lot more in the steering wheel. I could feel the bumps on the road a lot more. Now I am sure some of it is the stock arms probably have more give than the Currie as far as moving around and flexing so maybe technically it isn't joints I feel as much as the stiffer control arms. I cannot say for sure, but I definitely felt the difference after I changed my new Crowns to my new Curries.
I wouldn't say it bad; it is all how you like it. My Jeep is a little stiffer like a truck now, but with the stock arms it was more smooth like a car, but there was a ton more body sway with the stock control arms.
When I bought my TJ the stock arms were wore out. It had about 179K miles on it with what I believe were the stock control arms. I promptly changed them for new Crowns. I honestly didn't feel much if any difference. Then a few months later, I installed Currie control arms, and I could feel a ton of difference. To me the best way I could describe it was it went from driving a car to a truck. I could feel the road a lot more in the steering wheel. I could feel the bumps on the road a lot more. Now I am sure some of it is the stock arms probably have more give than the Currie as far as moving around and flexing so maybe technically it isn't joints I feel as much as the stiffer control arms. I cannot say for sure, but I definitely felt the difference after I changed my new Crowns to my new Curries.
I wouldn't say it bad; it is all how you like it. My Jeep is a little stiffer like a truck now, but with the stock arms it was more smooth like a car, but there was a ton more body sway with the stock control arms.
I'm not sure that any of us are in a position to find or provide non subjective data to determine if bushing composition makes a difference.
In my opinion, the only real way to know is to swap the control arms in the same vehicle with no other changes, but that's still subjective. I think all too often people make drastic changes in their Jeep and then give credit to just one aspect of the change. They can go from no lift on load e tires with blown out shocks to a long arm kit with custom tuned shocks and load c tires and then rave about how a long arm kit makes for a better ride.
I don't think it's fair for me to say that one bushing (and this usually comes down to Duroflex vs JJ) is better than the other if I haven't actually driven on the ones that I'm trying to compare on my own vehicle with no other changes. For what it's worth, I noticed no difference in the ride after swapping from factory control arms to Metalcloak control arms. Nothing else was changed.
In my opinion, the only real way to know is to swap the control arms in the same vehicle with no other changes, but that's still subjective. I think all too often people make drastic changes in their Jeep and then give credit to just one aspect of the change. They can go from no lift on load e tires with blown out shocks to a long arm kit with custom tuned shocks and load c tires and then rave about how a long arm kit makes for a better ride.
I don't think it's fair for me to say that one bushing (and this usually comes down to Duroflex vs JJ) is better than the other if I haven't actually driven on the ones that I'm trying to compare on my own vehicle with no other changes. For what it's worth, I noticed no difference in the ride after swapping from factory control arms to Metalcloak control arms. Nothing else was changed.
Take a look at the design of this PU bushing and give this some more consideration.
Notice the cut-outs in the bushing. How would these affect the elasticity of the bushing?
Compare this to the typical low-cost PU bushing for a TJ:
Assuming these bushings are made of PU with the same hardness (which they may not be), how would their elasticity be different?
One more factor to consider is that rubber bushings are often compressed at the time of manufacture and chemically bonded to the metal center sleeve and outer steel shell.
In comparison, the PU bushings are uncompressed (but possibly different hardness), and not bonded to the inner and outer components. How would that make a difference?
Are there any bushings or joints available for our Jeeps that have cut outs? Everything I've seen is effectively solid.
My instinct is that these differences may have a more pronounced affect on the misalignment or rotational characteristics of the bushing, moreso than the NVH.
The split bushings are they way they are for ease of installation. The fancy holes and slots may also be a marketing gimmick. Removing material should make for a softer joint, but at the expense of strength and resiliency. Then you end up changing the material in order to compensate for the compromises.
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So I finally looked up the Metalcloak shake table video, and I agree that it's hokey as all heck. There's so much wrong there that it's really just a distraction.
But Metalcloak did another video comparing CA joint flex. It's just as hokey, and I totally laughed out loud at it, but it's worth looking at what they're doing if you ignore what they're saying.
So they have four control arms mounted up, and they're flexing three of them until the joints contact the bracket. So they're showing us something about the joint design. But watch the guy's hands and face while he flexes the first three joints. That looks easy, doesn't it?
Then watch what happens with the final control arm with a rubber bushing that's more like the OEM bushing (although we don't know why they didn't use an OEM control arm). That thing is hard to flex! And when the guy gives up, the joint is nowhere near the bracket. It could go a lot further before it's flexed out.
So it's clear that if the control arm joint flexes along that axis, the different joint/bushing designs take a different amount of force to flex. How would that affect what we'd feel with our butt dynos?
But Metalcloak did another video comparing CA joint flex. It's just as hokey, and I totally laughed out loud at it, but it's worth looking at what they're doing if you ignore what they're saying.
So they have four control arms mounted up, and they're flexing three of them until the joints contact the bracket. So they're showing us something about the joint design. But watch the guy's hands and face while he flexes the first three joints. That looks easy, doesn't it?
Then watch what happens with the final control arm with a rubber bushing that's more like the OEM bushing (although we don't know why they didn't use an OEM control arm). That thing is hard to flex! And when the guy gives up, the joint is nowhere near the bracket. It could go a lot further before it's flexed out.
So it's clear that if the control arm joint flexes along that axis, the different joint/bushing designs take a different amount of force to flex. How would that affect what we'd feel with our butt dynos?
The stock arm suddenly becomes very interesting when you think about how the axle shifts and twists the bushings as well as the arm itself.
It is also worth pointing out that there is a significant difference between a 4200lb Jeep and a 250lb person enacting it's force upon a joint or bushing.
I don't have time to write everything down I want to contribute to this thread, but I will leave a couple thoughts / questions:
1) Think about the physic of a vehicle hitting a bump and where your bushings are. Does that bump impact the bushings?
2) Are we speaking of NVH or ride compliance? They are different things. NVH is typically something that will annoy you. Its that constant buzz you feel in your butt, or annoying rattle. Ride compliance is something more violent...think hitting a pothole. Its that jarring, rough ride feeling of having tires too full or shocks that are too stiff.
1) Think about the physic of a vehicle hitting a bump and where your bushings are. Does that bump impact the bushings?
2) Are we speaking of NVH or ride compliance? They are different things. NVH is typically something that will annoy you. Its that constant buzz you feel in your butt, or annoying rattle. Ride compliance is something more violent...think hitting a pothole. Its that jarring, rough ride feeling of having tires too full or shocks that are too stiff.
Totally. But a 250lb guy can fully flex some of those joints without breaking a sweat.
Think about hitting a pothole with one tire. One side of the axle is going to drop as the tire falls into the hole. That flexes the control arm joints along the axis in the Metalcloak video. Some of that force is going to be transmitted through the control arm back to the frame. Would it matter which control arm joint/bushing you had then?
In your pothole example, what about the influence of the sway bar or the shocks? Those two things are there specifically to control and influence that type of movement. What about tire pressure? To answer your question with a question, which is going to have the more perceivable effect?
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Absolutely! If you want to evaluate NVH, you can't look at a single joint in isolation. You have to look at how all the components work together.
Assuming the control arm transmitted less force from the pothole to the frame (which might be the case with a Johnny Joint), the axle is still going to move as the tire tracks the road surface. The sway bar is going to affect the axle movement, but the elasticity of the sway bar matters, as well as the elasticity of the bushings and links. The damping in the shocks is also going to affect axle movement. Rebound damping in the shock might actually keep the axle from falling as far, and let the tire deform more into the hole. You also have the spring isolator, which is damping some of the motion between the spring and frame.
And there are more joints and connections between frame and axle. Lots of things going on in that pothole example.
The point is, changing the properties of the control arm joint changes how the other components interact during suspension movement. If you can shift the suspension forces from a relatively hard linkage (like the control arm) to a linkage with more effective damping (like the shocks), you might get an improvement in NVH.
Interesting point. It is as if you are suggesting that it shouldn't necessarily be the job of the arms and their respective joints or bushings to damp the movement of the suspension.
I keep mentioning the track bar. The factory TJ suspension is a 5 link system. Four control arms and a track bar. We are focusing heavily on the control arm joints/bushings and their isolation. What about the track bar joints and bushings? Do they have any influence on NHV? Should the track bar be treated the same or differently than the control arms with respect to isolation.
Well no, not exactly. We were just talking about vertical axle movement and control arm flex, and how the other components play into that. Control arms are designed to move vertically, and the joints/bushings are designed to flex, some more easily than others.
But if we go back to the pothole example, the Jeep is going to exit the pothole, and when it does, the tire is going to impact the lip as it exits. Depending on the speed of the Jeep, the size of the tires, and the depth of the pothole, the Jeep is going to be subject to some force from the impact. Most of that force is directed upward, which is the motion we were previously talking about. But some of that force is directed rearward, opposite the direction of travel.
The shocks and sway bar aren't much use in that direction. The sway bar links even rotate in that direction, so they're doing nothing. The control arms are what's designed to handle that component of the pothole impact force. In this case, the main thing that's keeping that impact force from being directly transmitted to the frame is the control arm bushings. But this force doesn't twist the joint/bushing, it compresses it. I guess that's what the shake table video was meant to show, if it wasn't so hokey.
What do we know about the elasticity of various control arm bushings in this case? Not much other than butt dyno data, I gather.
But does the control arm bushing contribute to NVH in this case? Yes.
I know. You know where this is going, don't you? But one thing at a time.