... Especially w the short arms.
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.
... Especially w the short arms.
Anecdotally, we both replaced loose worn bushings with new tighter bushings and experienced improvements in NVH and handling. Interesting.I don't know anything about the shaker table, but as long as we're talking butt dyno, most of what I've done to my Jeep since I bought it was replacing old, cracked rubber with new OEM rubber. NVH decreases each time, and the ride improves each time.
No surprise there though.
Control arm bushings are next, so I'm watching this thread.
There are big differences in the elasticity of bushing materials. Check this out: https://www.acrotechinc.com/shape-factor-modulus-of-elasticity/Perhaps there could be a measured difference in bushing composition, but my guess is it would be negligible at best.
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.... Especially w the short arms.
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. View attachment 55939
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.
Take a look at the design of this PU bushing and give this some more consideration.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.
Take a look at the design of this PU bushing and give this some more consideration.
View attachment 55942
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:
View attachment 55943
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.
View attachment 55944
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?
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....
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?
Totally. But a 250lb guy can fully flex some of those joints without breaking a sweat.It is also with 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.
...
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?
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.In your pothole example, what about the influence of the sway bar or the shocks? Those two things are there specially to control and influence that type of movement.
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.
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.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 know. You know where this is going, don't you? But one thing at a time.I keep mentioning the track bar.