Well...that is what I am trying to figure out what you are trying to say. It is obvious (to me at least) that a body lift is completely different from a suspension lift. The lifts are 2 distinct methods that have only 1 thing in common: the word lift. That is why comparing a 5" suspension lift to a truck with a 2" body lift and 3" suspension lift is not an apples to apples comparison...because no one is saying that a body "lift" and suspension "lift" are comparable.
I get what you are saying...a 2" body lift adds height to the body/cab while only allowing an extra inch of frame clearance with bigger tires...so when compared to the same "lift" done wholly on the suspension, you get more frame clearance...AKA the body lift pushes the frame down.
I guess it then gets into the cost and fabrication of doing a 5" suspension lift vs 3" suspension and 2" body lift to fit bigger tires. I have 1st gen so I'm not sure on 2nd gen suspenion lift options.
NO
The body lift does NOT "push the frame down", in any way shape or form.
It has ZERO impact on frame height, period.
A "block lift" is a suspension lift, when the "blocks" are inserted between the axle and the leaf pack, when the leaf packs are on TOP OF the axle. IE: A "Block" LOWERS the rear of an X, because our leaves are UNDER the axle.
A BODY LIFT simply spaces the BODY up higher from the frame....the frame stays still, the body goes up...think of it as a taller body mount.
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There is NO POINT in "Comparing a BL to an SL" if its to see "Which is the better lift".
The BL is not really "A Lift"...its just picking the fenders up higher, so a rising tire is less likely to whack them....its more like trimming to fit larger tires.
So, lets say to want a suspension lift, 3" for example, and you have a
Gen II X.
You could fit 33's before the lift, and after the lift (With trimming/MM for either)...so, potential lift from adding 33's is the same with or without the lift....
...and, your 3" SL lifts the frame ~ 3".
The 33's lift the diffs, etc, by 1/2" or so over the 32's ground clearance.
You are a total of ~ 3.5" "taller" as far as ground clearance...over stock, and ~ 3" higher than if you had 33's on before the lift.
If you add a BL, to that 3" SL, nothing changes...its not needed as the tires already fit...and it doesn't lower anything in any way shape or fashion....your ground clearances are not LESS ANYWHERE.
This is why for < ~ 35's at least, a BL makes no sense on a Gen II. Cutting the fenders is probably better.
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If its for a
Gen I, then 32's fit stock (with trimming). If you leave the tire size alone and keep 32's...and add a 3" SL, your frame clearance is 3" more. Your diff clearance stays the same because the tires stayed the same.
If you add a 2" BL, your frame clearance says the same, because the BL doesn't change the frame clearance, and you do not lose any ground clearance anywhere.
As you now have room for 33's to rise w/o whacking...you can add 33's...and your diffs and frame go up about 1/2" higher than they were with 32's.
So, you have ~ 3.5" of total added ground clearance on 33's...all of which is from the SL and larger tire diameter - and the BL just made room for the tire to be larger, neither adding or subtracting any ground clearance in of itself.
So, cutting the fenders or a BL to fit 33's on a Gen I CAN make sense.
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The point is NOT that you DO get more frame clearance with an SL vs BL...I can't imagine that being a question...the SL IS FOR FRAME CLEARANCE...its why you do one.
ALL the BL does is TIRE CLEARANCE. If you don't need more room for a rising tire, there's no reason to get the fender out of the way.
There is no disadvantage to the BL if you want tire clearance...it doesn't hurt frame clearance, or any other ground clearances.
The frame DOES NOT GO DOWN when you add a BL. It also doesn't go up....it stays put.
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If ALL you want is tire clearance, using an SL raises the COG a LOT more than a BL would for the same clearance...and, removing the fenders is better than either in that regard.
Is the increase in COG a big deal? Not that often in some terrain, and quite often in others. The increase in frame clearance can outweigh the COG hit in some areas, and not in others...it depends where and how you wheel.
For rocks, etc, a higher suspension lift is really needed to get over stuff...but larger tires really help to roll over obstacles as well, so, the higher you are, and the larger your tires, within reason, if you have the power to use it all, you can get through harder stuff.
If you want to say a 5" SL is better than a 3" SL with 2" BL....sure, that's a different issue, but its treating the BL as a lift not as a tire clearance measure.
Its ~ the same as saying that a 5" SL is better than a 3" SL with no fenders....OK, but who was arguing AGAINST that?
Does a pure suspension lift raise the frame more than something that doesn't raise the frame? Yes.
Does a pure suspension lift raise the frame
more than larger tires? No, if the tire radius is 2" taller, the frame WILL be 2" higher.
Will a 2" increase in suspension height increase diff clearance by 2"? No, it won't change it at all.
Will a 2" increase in tire height (radius) increase the diff clearance by 2"? Yes, it picks up the diff AND the frame by 2".
Will, all else being equal, a 2" BL make room for a 2" increase in tire radius? Yes.
And so forth.
The ONLY nit I was picking is the statement that the BL LOWERED the frame...as, that's ridiculous...it simply doesn't lower the frame.
Think of a BL as an alternative to fender removal, instead of as "A Lift", and all of this will make more sense I think.