i am going through this now with a C-30 crewcab dually, trying to lower it down, but still keep it from being "slammed" and have a somewhat decent ride quality.
Lowering a truck though without air ride, you're still gonna have some issues with ride quality.
I am currently using a 2.5" dropped spindle, and from what i have been told, these actually mess with your steering/turning radius some, which i am kinda believing, even though a cc dually is a long bitch, it seems to have a wider turning radius than my old Freightliner did
I also originally cut the front coils down some, although i did it in too big of a step, and cut a coil and a half off...it sat LOW, (looked nice, but too low for me) and with still running the stock tires (1215/85/16) i had to remove the inner fender wells to keep the tires from rubbing,,,ALL THE TIME.
just finished up with the second set now, had another stock set i just cut 3/4 of a coil off, along with the 2.5" spindle and it sits just where i like it now, lowered, but not slammed.
As far as the rear goes, i am using the 2.5" shackles, they replace the rear shackles, and are just a bit longer, some underbed trimming may be needed, i haven't gotten around to it yet.
Also, i went and removed several of the rear leaf springs, (big rack) there was a spacer in my pack as well as the double overload (the one on top) i had to remove to get the rear down more.
it has a nice stance now, and still has some suspension movement for the bumps.
Personally, i didn't like the 2.5" spindle stance, yes it does lower it down, but it's almost not noticable.
If you like i will try to get you some pics of stuff in a bit.
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