These plates look to add around 1" to the bottom mount. As far as chatter, I can only see that happening at high speeds off road when the axle is articulating enough to let the bag move away from the bracket. If you notice that chatter when doing something that would create, you are pretty damn observant on the wrong things LOL.
With the minimum 5psi in my Airlifts they are touching the bottom mounting plate with my CB +2s. I can see this being a benefit on trails as it would allow the axle to continue to flex beyond the point of the bag to maintain traction. In example, the photo below I kept pulling my tire up off the ground and losing traction as the bag decreased my down travel. I'll add multiple angles for you to see, and because I am a photo whore.
I ended up having to back up and take a different line to get over this as I could not keep traction and all four wheels on the ground. The CB spacer would have helped a bit, but that axle being allowed to continue about 3" further down would have helped a lot more.
Another thought, while on the lift installing the shackles I had to disconnect the bottom of the bag. With the bottom of the bag disconnected the axle was allowed to drop another 1-2" beyond its connected state. Not much, but when you start to articulate the axle that can turn into a 6" or more difference (I am no engineer, I do not know the formula for figuring out an exact number). David's spacer will work for 95% of the people reading this, but for that other 5% a taller bag or something like this spacer would work better IMO.
