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**I posted this over on SoCal Tundras also. They have a pretty good suspension forum for more serious off-road applications, but I figure I could get a good answer here too**

I've been trying to figure out the answer to this, and haven't heard anything sensible yet. My main line of thinking is that the proper ride height could be achieved without putting a couple thousand pounds of top-out force against the suspension when the damper goes to full length. ~650-700#/in wound down 2.5" or so to get a level ride height lets the spring exert upwards of 2000# of force against the suspension, either to the bump stops, or against the sealhead circlip of the damper (if that is what limits droop). In any case it produces some **** ride quality. A slightly higher springrate will allow the same ride height, be far less prone to coil bind at full compression, and prevent harsh topping out.

Any other high end suspension setup, from both ends of my dirt bikes to my DH mountain bike to project formula cars that I've worked on, relies on very very little spring preload, and just adjusting the proper springrate to achieve the correct ride height. Any amount of preload more than a couple turns (to adjust for settling into corners), creates a godawful ride, similar to that of most trucks I've ridden in with coilover setups. Jouncy as hell, rebound that isn't strong enough, terrible top-out, trying to make the compression as light as possible for SOME compliance. I can't help but wonder how much better these setups could work with some more experimentation and letting the damper do what it's supposed to.

Can anyone shed some light on this? Anyone done something similar in terms of playing with springrates and had any success with it?
 

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My guess is that because one set of Coilovers has to work for different configurations of vehicles (std, ext, dbl cab, etc) It is much easier to adjust preload for height than to try and have a bunch of different coil springs.
This makes the most sence, along with the fact that different folks will want their ride height at different levels. So for their standard product they offer an "average" spring rate and let you tweak it from there with preload.

I plan on getting a coilover setup in the next few months and as long as the price difference isn't too huge I will likely try to custom order mine with the correct spring rate and valving to achieve my desired ride height and handling based on my vehicle setup, average payload, and typical road conditions (terrible dirt/gravel/mud/sand roads that develope washboard that will shake your truck apart and potholes that you could darn near loose a truck in, for a week straight, and then pavement for a week!)

I'm no expert but I've done some shock work with DH mountain bikes and I completely agree that too much pre-load is a bad thing (fully compress your coil before the shock can dampen bottom out, loads of top out force). You should always use/adjust spring rate to set your sag (lift) and some minor adjustments to preload for fine tuning.
 
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