Defender, that's a very insightful question.
Hope you guys have some reading time
. Read all the lift related links in my signature line, the theory applies to any vehicle with this type of suspension.
Here's an example shock, fully extended:
OXXXXCXXXXXXXXX=======O
The
Os are mounting eyes. The
C is the spring seat.
Xs are the shock body.
= are the shock shaft. It doesn't matter which end is up or down, but let's call the left side, with the shock body, "up".
We have coilovers (the coil goes around--"over"--the shock), but there's no reason the coil needs to be around the shock, it just takes up less space. Here's an example spring, next to the shock since I can't put text over other text...it's easier to see like this, and just as valid. The dashes are just for placement since the forum software "eats" whitespace, the
Ss are the spring:
OXXXXCXXXXXXXXX=======O
------SSSSSSSSSSSSSSSS-
That's an unloaded spring, no weight on it at all. On my truck, that's a few turns of the adjusting collar away from a loose spring. On a stock truck, it's loaded enough to keep the spring from moving, and probably to load the spring such that any effect on rate in the first inch or so is minimized. Yes, it's preloaded, but hold that thought...it may not be "preloaded" once you put it on the truck and the truck's on the ground. Let's pretend this coilover is like mine, since it's easier to understand. The spring is held in place by a threaded adjusting collar (the shock body is also threaded), and the collar is turned down just enough that the spring doesn't rattle when the coilover is completely unloaded.
Now let's put it on the truck.
The truck's weight will compress the spring an amount consistent with the spring rate. For a 600# spring, that means it takes 600# to compress the spring one inch...so 1200# will compress it two inches, and 1800# puts it down three inches.
Let's also designate each character as an inch, so that shock above has 7" of travel, and it's 23" long (for the sake of ASCII art alignment. Normally you'd measure between eye centers).
Let's say the front of your truck weighs 3600#, with the weight centered side to side. Each coilover will take 1800# of that weight, compressing the spring 3" on each side. The shocks now look like this:
OXXXXCXXXXXXXXX====O
------SSSSSSSSSSSSS-
It's normal for these springs to compress at least 50%...in other words our 16" spring can compress 8" until the coils rest against each other. We've just compressed it 3", there's another 5" (at least) of spring travel remaining, and 4" of shock travel remaining.
Now let's lift the truck. Turn the collar down, set the snap ring at a different groove, whatever. Here's what it will look like
off the truck, if you shift the collar down an inch:
OXXXXXCXXXXXXXX=======O
-------SSSSSSSSSSSSSSS-
Oh noes, it's preloaded! Stop throwing that misunderstood term around and wrench it on, and it will look like this:
OXXXXXCXXXXXXXX=====O
-------SSSSSSSSSSSSS-
I swear on my left nut that if you haven't preloaded the spring past where the truck will load it, that spring will be the same length as it was the last time you had the assembly on the truck. The only difference is the shaft is now 5" out instead of 4" out, and if these were mounted in a 1:1 travel ratio, your truck would now ride an inch higher. Our trucks have more like a 1:2 ratio, so for us that'd be more like a 2" ride height adjustment.
Now let's lift another inch. Same as before...turn the collar down. Here's how it looks on the truck:
OXXXXXXCXXXXXXX======O
--------SSSSSSSSSSSSS-
Notice! That is an 8" travel spring, with the truck's weight taking up 3" of travel, but now you have
six inches of shaft exposed but only
five inches of available spring travel. The coil will lock, meaning the winds will sit against each other, before the shaft is fully compressed. In all likelihood that also means before the control arms hit the bump stops, which usually leads to damage at the coil bucket (I bent the coil buckets as well as the 1/4" mounting plate, which is secured with a trio of "grade 10" fasteners!). In the real world, springs are often guaranteed to have at least 50% compression...ie a 16" spring should compress
at least 8", and so forth. Sometimes it's better than 50%, it all depends on the wind, but use 50% as a good estimate.
You can measure your springs easily with calipers...measure the distance between the winds, and the diameter of the winds, and do some simple math to see if you're going to bind the coil before you collapse the shock.
Now let's add an upper control arm. There's no way to accurately depict this without graphics, but we can use some simple pictures of shocks again. Let's say the stock joint binds with any coilover longer than 24" eye to eye. So far, our coilovers work just fine...this joint is not at risk with our 22" assemblies.
So we add a block on top. This could be aluminum, polyurethane, steel, welded steel, Delrin, wood, hockey pucks, whatever. Same thing, in the end. Anyway, it's the
T for "Top Load". The upper arm extent is the
As.
AAAAAAAAAAAAAAAAAAAAAAAA
TOXXXXCXXXXXXXXX=======O
-------SSSSSSSSSSSSSSSS-
Ooooh! There's no "preload"! It's just like stock!
No, it is
not just like stock. It might be, but we have to measure, because the shock body may be lower than a bumpstop. Bumpstops are configured to land long before the shock collapses, and compress completely before the shock is completely collapsed.
AAAAAAAAAAAAAAAAAAAAAAAA
OXXXXCXXXXXXXXX=======O
------SSSSSSSSSSSSSSSS-
>>>>>>>>>>>>>>>D
So go measure those bumpstops. For our example:
AAAAAAAAAAAAAAAAAAAAAAAA
TOXXXXCXXXXXXXXX=======O
-------SSSSSSSSSSSSSSSS-
>>>>>>>>>>>>>>>D
Looks like it'll still barely work. There are some spacers that operate like this, with a very thin top-load shim (Daystar), and some shocks with a similar total length (Bilstein). Like Jerry originally said,
most spacers are bad...not all.
Compare this with a non-adjustable coilover and a block installed inside the assembly (and one still on top) and it's the same...
I for "In Pack":
AAAAAAAAAAAAAAAAAAAAAAAA
TOXXXXCIXXXXXXXX=======O
--------SSSSSSSSSSSSSSS-
>>>>>>>>>>>>>>>D
This is how the Daystar kit operates. Hopefully by now everyone understands that a complete replacement for the stock length coilover is no better than an in-pack spacer, if the shaft is the same length.
Now we use what's above as our basis for comparison. Let's say you add two inches of top load spacer:
AAAAAAAAAAAAAAAAAAAAAAAA
TTOXXXXCXXXXXXXXX=======O
--------SSSSSSSSSSSSSSSS-
>>>>>>>>>>>>>>>D
Now you get two problems. The shock will collapse before the suspension hits the bumpstops, and when fully extended will push beyond the limit of the ball joint. That is most of the top-load spacers on the market, including the picture I posted above and all variants, and leads to the pictures Jerry has in the original post for this thread.
There's another solution on the market...longer shafts. Bilstein has the lowest-cost option, and hopefully some people will respond to my other thread with measurements so we know what we're working with. You can probably get very nice complete replacements with similar shaft extension lengths from Camburg and IVD. These won't hurt your joints either...in our model, they'd look like this:
AAAAAAAAAAAAAAAAAAAAAAAA
OXXXXCXXXXXXXXX========O
>>>>>>>>>>>>>>>D
Note the shaft length won't compromise the upper joint, and the body length won't allow collapse before the bump stop hits. The spring goes where the spring needs to go, just be certain you won't lock it up.
If anyone still doesn't get it, you're banned. No, just kidding. But I'll be pretty disappointed.
If you want to know how much top-load spacer is safe, you need to help us all out and
MEASURE a few things on your truck.
ZERO: Put one front corner on a jack stand, pull the wheel, mark your alignment cam positions, loosen the cams, and pull the coilover.
ONE: Measure the total extended length of your stock coilover, to the best accuracy you can achieve. Just take the whole bloody unit off the truck and measure from the top of the mounting surface to the center of the eye.
TWO: With that coilover off, go look at your front suspension...I bet, when you removed the coilover, the front suspension dropped a little more than when the coilover was in place (at least, it did if you loosened the alignment cams). Measure from the mounting surface in the coil bucket to the center of the eye on the lower control arm. Your suspension is now hanging from the upper ball joint. Whatever the difference is between that measurement and the length of your extended stock coilover, that's how much top-load spacer you can run before you damage the upper ball joint.
THREE: Hope you have a spring compressor handy, because you need to pull the coil. Take the plastic shield off the shock while you're at it, so you can see the shaft.
Measure the thickness of the metal portion of the bumpstop and then remove the bumpstop from the truck. Put the shock back together on the truck
minus the coil. Now cycle the suspension upward (you'll need a jack, the shock is pressurized) until it's almost to the frame...only as far away as the metal portion of the bumpstop.
Examine the shaft. If there's any chrome showing, measure it. This is how much top-load spacer you can run before you damage the shock.
Whichever of the two measurements is smaller, that's the thickness of the largest top-load spacer you can run without damaging the vehicle, period. If you're a manufacturer, feel free to raise your hand if you've done this,
so I can call BULL**** on about 90% of you.
If you have a 2nd-gen in the Denver area and are willing to take it apart and do this (I will help), let's schedule a day...might have a truck ready, but I know he's pretty busy, and besides it'd be great if there were a few people around to help, drink beer, laugh at our mistakes, etc
.
Unfortunately until somebody measures all that, we're shooting in the dark. I do have the measurements from the Bilstein 5100s for the 2nd-gens, provided by one of our vendors for exactly this purpose
. As soon as somebody puts a ruler to their OEM equipment we can answer everyone's questions.
For future reference, Tundras (all of them) have a double wishbone coilover front suspension, and a leaf sprung live axle rear suspension. If you have a heavy truck, you need a greater spring rate to carry the additional weight, not necessarily a "coilover"...which would mean a new shock
and a new spring...tho if you change the amount of weight or the spring rate, you've likely changed the suspension frequency and will also likely want to change the valving...at which point you really will be shopping for a new spring and a new shock, aka "coilover".
Hopefully that answers everyone's questions and a few that haven't been asked yet, as well as explains
why nobody has a straight answer yet for whose kit has how much travel or is downright dangerous for your truck.
Will somebody please measure this stuff? Discussing suspension should not be like arguing politics.
-Sean