coil preload question

is it the coil that determines the amount of lift or is it the length of the shocks?

I am thinking it is the coil. So compared to stock height, if I set 5100 at 1.75", then I get 1.75" higher lift right? Then where does the coil preload come in? If there is preload, then the spring is getting compressed, then that means setting the 5100 at 1.75" will add no lift? or is the coil compressed less than 1.75" so there is still some lift? if so, how much?

thanks

 

this is exactly the part that seems self contradicting.

lets say for discussion purpose the coil height when installed is 20" with 5100 set at 0". If the 5100 is set to 1.75", you say the coil is compressed. If it is compressed by 1.75", then the coil height becomes 18.25", so effectively there is no additional lift, no?

my thinking is, if 5100 is set at 1.75" and the truck gains 1.75" lift, that means the coil is not compressed, right? otherwise, clearly there will be no 1.75" lift if the coil is getting compressed. so where is the coil preload/compression?

 

the height is determined by the distance between the top of the coil and the bottom of the shock (that attaches to lower control arm), correct?

so to add lift, we either use a longer coil, or extend the 5100 shock below the spring seat or both right?

is the upper control arm introducing the compression? or replacing the UCA is only needed when using wider tires?

if so, then regardless if you use a longer coil or extend the 5100, there has to be compression right? the only difference with using a longer coil is the shock downward travel is not reduced.

I just need an explanation/clarification why setting 5100 to 1.75" provides 1.75" lift even if coil is compressed. or explain the relationship of coil length, 5100 setting to the amount of lift.

please use the diagram below to make the explanation clearer.
thanks

 

sorry, I still am not able to follow to make sense of it. I guess you have to dumb it down some more.

I follow the part of 1.75" setting is extending the shock below the spring seat by 1.75", hence the part above the spring seat remains the same. What I don't follow is where is the coil compression? and if coil is compressed, regardless by how much, then that effectively reduces the lift, hence it contradicts setting 1.75" gives a 1.75" lift.

isn't compressing a coil will make it shorter?

 

He has been very patiently trying to help you. First off, try Google-ing for images of adjustable coil over suspensions. The concept that you are missing is that the adjustment moves the lower seat of the spring upwards. As the spring ratio is higher than the weight of the vehicle on that location (or else the spring wouldn't work too well) there is a greater amount of vehicle lift by a lesser amount of spring compression (preload) due to the leverage provided by the moment arm of the linkage (see kinematics).

If you have a see-saw and move the fulcrum away from the center then the travel for each end is no longer equal. The upper and lower control arms act like a lever to the frame and 1 inch of movement at the spring will equal two inches of travel at the frame (I'm not sure of the ratio).

 

So does this mean that if ur preload is the same as load weight, ride would be relatively stock, both in height and ride quality? I know that a 3/4 or 1 ton rides much better with a load so is that the same principle?

 

ok, thanks for the reply. I'm slowly trying to follow this.

this is how I understand your logic
if you say coilover length remains the same, but the truck has to apply however amount of force to overcome the 1.75" compression before the coil comes down further, then wouldn't that mean there is no lift?



say the coil drops 1" when truck weight is added.
when it is off the truck, the coil springs back up to unloaded length. I extend the length below the spring seat by 1.75". my thinking is the coil unloaded length is still the same (the shock extends, just like when you hit a pothole, the shock will extend).

or are you saying the spring is not applying enough force to the shock to extend it, hence the shock ends up compressing the coil?

but if the shock function is for dampening, wouldn't it settle to the equilibrium length of the coil? in this case, the unloaded length? therefore the shock must extend to the length of the unloaded coil?

So I don't follow why you say the shock length remains the same and does not magically get longer or shorter.

if the unloaded coil length is the same, this makes the effective coilover longer by 1.75" unloaded. Then when you install on the truck, you add the weight of the truck, then the coil will come down as before with stock setting. hence the effective lift is 1.75".

what you are saying is, the coilover length does not change by setting to 1.75". but instead, when you add the weight of the truck when installed, it does not drop any further? my thinking is it will still drop the same amount.

do shock length always go back to the center regardless of load? that seems to be the reasoning for compressing/preloading the coil. perhaps this is the information I am missing.

I know it is getting a bit convoluted, but I don't know if anyone else is following my logic, and explain why it is wrong. I'm not saying my logic is right, I'm simply trying to understand how this all works.

thanks again for trying to explain.

 

if the coil does not compress further when adding truck weight due to the preload, but the preload shortens the spring (by 1.75"), then where is the lift?

if on stock adding the weight of the truck compreses the coil say 1".
If preloading the coil with 2.5" of force to make the coilover length the same. Then I put the weight of the truck and coil does not compress further due to preload, then I only gain 1" compared to stock right? so why vendors and bilstein and others who set to 2.5" say they see 2.5" lift? it does not add up.

say total unloaded (or stock shock loaded, equivalent to 0" setting) coilover length is 20". set 5100 to 2.5" to compress spring, overall uninstalled length is still 20". with stock, effective height is 19", with 5100 set at 2.5", effective height is only 20".

I can follow why the ride will be stiffer since you now need more force to compress the coil further, and will bottom out sooner since there is already the pre compression. but I still cannot see where the lift is.

 

This brings up an interesting debate.

I bet if you measured the length of the coil with the strut in the truck on its own weight... the coil length would be almost identical at the 0 setting and the 1.75 setting... its just there is more lenght of shock below the bottom of the coil to achieve the lift.

Yes initially with the strut not in the truck there will be more preload, but under weight the coil is close to the same length.

 

Try this, it's a good quick read: http://www.zoomsquared.com/technical-information/coilover-spring-preload-explained

 

If you look at this image, and move the lower spring mount up the strut/shock shaft, but keep the length of the spring constant, the strut/shock extends, and the 3-7/8" dimension decreases, lifting the truck, or lowering the spindle in relation to the frame.

 

thanks boone for the link. that explains preload. I think it can be improved to explain how lift is gained. The article is correct that it is counter intuitive. I just question things and not accept it as it is. It has to make sense. but in the end, once explained properly, it is logical.

I think for this to make sense, I suppose on a stock spring, if you install it onto the truck, the coil has to compress > 2.5".

if the coilover overall length remains the same, but coil is preloaded 2.5", then when installed, the truck will simply compress the overall coilover length by 2.5" less. (say without preload, coil shortens by 3", with 2.5" preload, it only comes down 0.5").

example calculation with hypothetical numbers
no preload coilover is compressed from 20" to 17" when installed.
with 2.5" preload, coilover length is still 20" and compressed by 0.5, for final length of 19.5". That looks like a gain of 2.5".

so its like using a stronger spring. of the same length. the ride will be stiff either way.

if you use a longer spring with same K factor as stock, then this will make the coilover longer right? and is the only way to get lift with the same ride stiffness as stock?

 

You got it, pretty much. Try and think about preload in terms of weight and energy and not length.

 

according to hooke's law, force is directly proportional to length (distance from equilibrium). either way should work but just easier to grasp in terms of length, since after all, we are talking about lift, which is length.

here's another wrinkle to this, now about ride stiffness

now since I do not know how much the stock coilover is compressed and just used 3" hypothetically. I can see why a lot of folks using 5100 do not notice a (significant) stiffer ride.

if the spring is normally compressed 3", it is still essentially compressed 3" even with 2.5" setting on 5100 correct? (2.5" precompressed,+ 0.5" after install).

so why would the ride/stiffness be any different?

at the equilibrium point after installing the coilover back on the truck, the spring compression is the same regardless of 5100 spring seat setting.

is it the dampening effect of the shock that is causing the stiffer ride? It certainly can't be the springs.

 

This is another real world scenario that differs from paper. A linear coil should not "change'' spring rate through it's cycle, as it is linear and not progressive. The spring rate does not change under preload but the ride is stiffer as a result of the coil already being compressed. The 5100's are valved a little stouter than the 4600's but not enough to change the ride severly. Not to be a dick, but with your new found knowledge of preload, jberry pretty much nailed it.