alright i guess i gotta go extra mileto list out reasons when a simple youtube search can yield videos with more articulate presentation and visual aide that do better explanation than i do. I'll do my best to make the explanation relatable. bear with me.
-Limited Travel
here's an over-simplified example. you are limiting your suspension down travel. Suppose your suspension has a travel of position 1-10. At normal ride height your piston inside the strut is sitting at position 5, middle. When your suspension is going over bumps it compresses, making the piston move up to position 6, 7, 8, etc. You have 5 positions to go. On the other hand, when you're going over dips, potholes, etc it droops, so your piston moves down to position 4, 3, 2, etc.
Now, spacer lift pushes your piston down to create that "lifted" look instead of adding more length to your strut. So now your piston at ride height is at position 4, 3, or even 2 and you don't have anymore downward travel that is needed to absorb the impact when going over dips, potholes ,etc., and now it's the bottom of the strut absorbing all the impacts. Your UCA is extended and so is your ball joint, and therefore your UCA ball joint now serves as your limiting device for downward travel. Basically, you are asking your UCA to do something it's not designed to do. In addition, your upward travel is now not limited by the bump stop, but solely rely on the shocks that are less than 2" in diameter. Hit it hard enough and it will bend or break.
On the other hand, suspension lift kits with struts and springs add more length to your strut and proper spring rate. So you have more space in each position. You're still at position 5 at ride height, even lifted, because each "zone" for each position is bigger. You retain your travel and each component retains its function without being asked to do what it's not supposed to do (like ball joint acting as a up travel bump stop or your shock acting as a limiting strap.
Now, some people say you can just add UCA and diff drop to eliminate those issues. True, you can, but that still does NOT solve the issue of limited travel. And you're still not utilizing the bump stop to help disperse the force of impact, and you're still asking components to do things they are not designed to do.
See this animation by Accutune here:
https://accutuneoffroad.com/wp-content/uploads/2022/11/coilover-with-top-hat-spacer-animation.gif
-Stiff ride
Because you are limited suspension travel, any imperfection on the road is passed on to the truck. IF you live in places that has terrible roads like California, where you cannot go one mile without finding a pothole or crack on the road and they take forever to fix/ fill, you will feel it as you go through them. And every time you feel it, you are just adding more stress to your suspension.
Your suspension doesn't know on-road and off-road. The only differences between the two are: intensities of travel, frequency of travel, and intensities of impact. Offroad just intensifies all the above. Again, overly simplified estimation here: IF your spacer lifted shock has life expectancy of 2 years on road, offroad reduces it to 1 year or less due to more intense travel, more frequent travel, and more frequent impact.
-Why I call it mickey mouse
Your suspension needs travel to do its job. Adding spacer lift takes away travel and therefore, prevents the suspension from dampening the ride for the look.
That's like adding a HEMI badge to a Pentastar equipped vehicle. Or what I found on my customer's DIY wiring job after removing layers of e-tape:
View attachment 161922
Does it work? Yes, it does. Will it start a fire? Probably not. Is it safe? No, it's not. The correct way to do this is to use connectors and heat shrinks, but somehow dude thinks doing it this way is "just as good" and "more economical." That is what spacer lift is like. Mickey mouse.
-Regarding some think Bilstein is stiff
That is due to valving. There are various types of valving in suspension and different companies use different types of valving system. That's a whole another topic that's not relevant to topic on hand. Reason why I said "at least" Bilstein because it is the only shock company that strikes a balance among quality, affordability, and longevity. There are some other companies' products... let's just say, quirky.
-Suspension is wear item. There's is no one set of suspension that can serve you for life. King and Fox will need to be rebuilt at some point (depends on your usage). Bilstein 5100s will need to be thrown away at some point (again, depend on your usage) due to their sealed design. Maybe start looking at them as your tires, brake pads, etc that are wear items can help you change the way you see things.
Hopefully my explanation is good enough for you. If not, just read what AccuTune wrote here:
Spacer Lift vs Preload Spacer vs Coilover Preload - AccuTune Off-Road
There's a reason why I'm a tech/ outfitter and not a teacher.
