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Old 11-01-2013, 01:05 PM   #1
philipho
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Default Uneven Coilover preload

Hi people,

The height of my car (08 wrx hatchback) is pretty even all round. ~14 inches from mid of rim to fender. I have coilovers installed.

Alignment is also done with 0 toe all round, -2 camber for front and -1.5 rear.

Today I noticed that the right rear coilover spring is much more compressed compared to the left rear.

Right:


Left:



The right side looks way more compressed (pre-loaded) than the left, is this normal?
The car is not corner balanced yet, just setup to be even aesthetically.
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Last edited by philipho; 11-01-2013 at 04:28 PM.
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Old 11-01-2013, 01:12 PM   #2
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It's hard to tell from the pictures, but I think your spring preload may be off... a lot. Take measurements of both springs in mm and get back to us. Did they come pre-adjusted? Did you compare both of them side by side before installing? Is this the krusty krab?
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Old 11-01-2013, 02:10 PM   #3
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Originally Posted by Mr Wrex View Post
It's hard to tell from the pictures, but I think your spring preload may be off... a lot. Take measurements of both springs in mm and get back to us. Did they come pre-adjusted? Did you compare both of them side by side before installing? Is this the krusty krab?
Yes the preload are different, measuring just the length of the spring, the left is ~6.5", the right is ~5".

I don't know, in both pictures, there is a white marking right at the plate where the preload is adjusted. Seems to me those are the markings that come with the coils from the factory.. So maybe it is adjusted this way for the 08 hatch.

I also read somewhere that preload does not affect handling and performance since my coils have independent ride height adjustment.
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Old 11-01-2013, 03:34 PM   #4
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Ok well there's a big ol' problem right there. You have linear springs on your coilovers and by increasing the spring pre-load, you're pretty much increasing the stiffness of the spring. You want to make sure those are even on both sides and then you'll want to re-adjust the ride height to make sure both sides are even. If you keep them the way they are now, your car will handle pretty funny (I'm assuming you've noticed this by now?).


If you want to know a little more detail about spring rate and all that jazz, read this:
http://zilvia.net/f/tech-talk/58103-...tml#post513617
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Old 11-01-2013, 04:20 PM   #5
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Hi Wrex,

If I understand linear spring behavior correctly, what sykikchimp mentioned in your link is incorrect.

If the spring is already preloaded with 700lbs (compressed by 1 3/4inch), and if you put a car of 700lbs additional on that spring, it will travel another 700lbs (1 3/4 inch) in addition to the preloaded 700lbs.


The thread below mentioned that the amount of preload does not affect performance, it only changes the amount of travel of the spring.
http://forums.nasioc.com/forums/showthread.php?t=838630

So what it means for my case is that the handling of my car is the same. However, the possible suspension travel for my right side is 1.5" lesser than my left.

Anyone with experience in this area please correct me if I am wrong.
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Old 11-01-2013, 04:54 PM   #6
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Mmm yea you're right... I only skimmed through the explanation since I'm at work and half paying attention His wording is a little too vague and probably targetted towards a noobie audience. Like I said, I'm terrible at wording how preload affects travel, so I had to use "google translate" to turn my shoddy explanation into something that makes sense. That post definitely didn't though...

I'm fairly certain that the only reason to have uneven spring preloads is to corner balance the car, but hopefully a real guru can chime in.
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Old 11-01-2013, 05:38 PM   #7
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I did more reading. Actually sykikchimp is correct.

These 2 sites explained it very well:
http://www.sonicsprings.com/catalog/...ch_article.php
http://www.zoomsquared.com/technical...load-explained

In my case, how should I resolve this?
Jack the car up, make sure that the preload is set to factory recommendation, then adjust the coilover height?
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Old 11-01-2013, 06:47 PM   #8
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Yea. You always want to adjust the preload first. What I did on my feal 441's is tighten a few turns and then, with my hand, rotate the spring around to check how loose it is. Once it felt snug enough, I stopped and measured the preload and applied it to the other corners. If any of the corners are loose, re-adjust and check all four again until they are all the same. Once that's done, adjust the height and you're good to go.
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Old 11-01-2013, 10:44 PM   #9
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Quote:
Originally Posted by philipho View Post
Hi people,

The height of my car (08 wrx hatchback) is pretty even all round. ~14 inches from mid of rim to fender. I have coilovers installed.

Alignment is also done with 0 toe all round, -2 camber for front and -1.5 rear.

Today I noticed that the right rear coilover spring is much more compressed compared to the left rear.

Right:


Left:



The right side looks way more compressed (pre-loaded) than the left, is this normal?
The car is not corner balanced yet, just setup to be even aesthetically.
First off, a GR will not have naturally equal ride heights on each corner. In fact if you conner balance your car the total corner heights will vary by as much as 1/2". Your coil overs should not adjust ride height by using the upper locks that should only locate the spring. Generally mfrs recommend a slight spring preload 0f approx 1/8" (2mm). It would be unusual to ever change the preload unless you were racing and tweaking your setup for a specific track.

On your coil-overs the lower ring that locks the center threaded body into the lower mounting bracket and is used to set ride height. It is pretty easy to reset on car. Just loosen lower clamp at mount, then twist or use the "adjustment tool" to turn the body by leaving the upper clamps tight.

If your ride height is at the level you want (and you want to leave it that way), then measure the height of the total coil-over height from the top of the lower mount to the the top of the spring. Now reset spring preload heights to mfrs recommendation. After doing that your ride height will have dropped by the amount you changed the spring height. For example, if the spring is lowered 5 turns (or 1/4"), then raise the body height the same amount to get you back to the ride height settings you had.

I recently corner balanced my 2011 STI and kept as close to 14" frt, 13.75" rear center to fender heights as the starting point. After the balance the settings for ride height measured from the ground to the lower fender lip is: LF 25 3/4", RF 26 1/8, LR 25 7/8, and RR 25 5/8.
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Old 11-02-2013, 12:14 AM   #10
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There seems to be 2 different opinions on how preload works.

Opinion 1:
Let say we have 10lb/inch spring that is already "preloaded" 1".
You then put 5lbs on the spring without any other weight on it, the spring WILL NOT compress.
It will only start compressing if you put >10lb of weight on it.

Opinion 2:
Let say we have 10lb/inch spring that is already "preloaded" 1".
You then put 5lbs on the spring without any other weight on it, the spring WILL compress by 1/2"


I feel that opinion 2 is more logical.
Which is CORRECT??
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Old 11-02-2013, 04:46 AM   #11
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Does it really matter how preload works? Just even them out to where you want them.
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Old 11-02-2013, 09:44 AM   #12
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Yes it matters adjusting the preload requires me to bring the car to the workshop (quite a distance), I might need an alignment which is another place that I need to drive to.

If opinion 2 is correct, I will just leave it as it is.
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Old 11-02-2013, 10:29 AM   #13
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I have a 2011 sedan with ISC N1 and my rears are the same as this picture yet the car drives fine handles fine and sits perfectly level. Alignment is good, no uneven tire wear over the last year.
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Old 11-02-2013, 01:39 PM   #14
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Quote:
Originally Posted by 1wrx1 View Post
I have a 2011 sedan with ISC N1 and my rears are the same as this picture yet the car drives fine handles fine and sits perfectly level. Alignment is good, no uneven tire wear over the last year.
Mine handles fine too for just normal street driving. It feels great on the road and does not pull to any side. Just did an alignment too and everything is perfect.

But I think we will see the difference if we do hard turns on a track. My left coil, which has less preload, will be able to travel a longer distance as compared to my right side, which will encounter coil-binding earlier.
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Old 11-02-2013, 03:32 PM   #15
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^^ the pre-load on a linear spring won't affect the spring rate bc its linear, as long as it doesn't coil bind. Having spring collars at different heights is not unusal, especially on units that set ride height w/the adjustable spring perch. These units have separate height adjustment and by using the lower collar to set height you'll optimize/balance the stroke length on all sides. Is it critical on the street? Probably not!
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Old 11-03-2013, 03:26 AM   #16
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Linear springs are only "linear" to a certain point before physics can't help but spoil your day.

http://store.worksmotorsports.com/Sw..._p/swi.210.htm

Based on the coilovers you have, that amount of preload may be more drastic compared to higher end "more linear" springs.

You may want to just go to a reputable corner balancing shop, tell them your concerns, and have true peace of mind after corner balancing your car for whatever kind of driving you want to do.

Sure, it's inconvenient and costs money, but is trusting people on the internet, who are potentially less knowledgeable in this subject, and have the little ounce of doubt a better alternative?

Have you contacted the manufacturer of your coilovers regarding this matter? Another option is to contact a reputable suspension vendor here on NASIOC that would likely know more that we can provide.

Anyhow, I hope you find your answer and have fun driving. It sucks hard to have looming questions and doubt especially in matters of suspension tuning.
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Old 11-03-2013, 08:38 PM   #17
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Great chart! Thats why you pay 20-30% more for Swifts.
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Old 11-03-2013, 09:19 PM   #18
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Haha, preload.

Unless the damper is fully topped out, as in can not extend any further, preload ONLY raises ride height and has zero effect on effective spring rate. All you are doing with preload is lifting the car and adding bump travel range while sacrificing droop travel range. That's it. You are picking where in the dampers travel you want it to be when the car is sitting. If the damper has 5" of travel and you want 3" of bump and 2" of droop travel, you will add preload until the damper is extended enough to have 3" of travel. Let's say we have 1000 lbs of chassis on that spring and we run a 250 lb/in spring. The chassis will squish the spring down 4" once loaded. With zero preload the spring will be compressed 4" down from full strut extension. If the damper only has 5", we only have 1" of bump travel remaining and 4" of droop travel remaining. Now we add 2" of preload to the spring. What this does is push the chassis up farther and subsequently extend the damper farther at rest. Now we have 2" of preload force + 2" of compression due to the 1000 lbs of chassis on this spring. We end up with 3" of bump travel remaining before bottoming out the damper and 2" of droop travel. This is how preload is used.

Now this damper shown also has ride height adjustment. This lets you raise or lower the chassis without affecting bump and droop travel. If you want to raise the car 1", you can spin the tube around a bunch of times and relock down the collar 1" farther down on the threaded section of the damper. Now the chassis is pushed up 1" but we did not affect bump and droop range. We could ignore the ride height adjustment and simply add 1" of more preload to do the same thing. Again, we would raise the chassis 1", but this time we would also change bump and droop travel, ending up with 4" of bump and only 1" of droop range. With most of our basic macpherson struts and cheaper aftermarket struts and coilovers, all we have is preload adjustment. We can lower the car only with shorter springs and less preload and we throw away bump travel to do it. This is why ride quality ends up sucking on lowered cars. We end up with 1" or 2" of bump and then 4" or 5" of droop travel we never use. We throw away all of our bump travel so the car bottoms out over EVERYTHING. It becomes important to buy products with both preload and ride height adjustments to let you tweak bump and droop ranges to make the car ride the best. Typically, ideal tends to be around center. If the coilover has 5" of travel, 2.5" of bump and 2.5" of droop are pretty ideal. If damping is soft in compression and stiff in rebound we may want to add a little more bump travel since the damper is soft and compliant in that direction. It will more readily soak up bumps but also use up more range of travel in that direction. This is also why lowering on stock dampers sucks because compression damping is very low on oem cars making the car very readily bottom out when there isn't enough soak up bump travel.

Back to the pics provided by OP, it does seem like something is amiss, but it may be more deceiving than you think. Side by side and sized equally, it does appear that the one coilover has preload set higher. However, it also appears that the dust boot is higher, possibly indicating that it is simply more compressed. I just don't know if the dust boot slides over the threaded section or stops at the top of the wider, threaded section of the damper. If it stops at the top of the wider section, it appears that the one coilover is just more compressed, i.e. more of its travel used up. It also appears the ride height was adjusted on that damper too, as can be seen from the rusty section above the collar. I don't know why this was done, but it will load that corner more. It's possible that corner is heavier and needed that or it may be due to a setting offset at the opposite end of the car. If the front end of the car at the opposite corner is set wrong, it can throw that back corner off.

Ideally you should remove the coilovers, inspect them, set both sides equally, and reinstall. Do that for both the front and back and then re-evaluate the ride height. It's likely they where not set up properly to begin with. Don't assume things are correct until you've checked them yourself. You don't specifically have to remove the coilovers to adjust them, but you will need to lift the car off the ground and unload the suspension. Adjust the collars to set. You may need to disconnect one end of the coilover to spin the damper to adjust ride height.
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Old 11-03-2013, 09:27 PM   #19
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Quote:
Originally Posted by jaboyd View Post
Great chart! Thats why you pay 20-30% more for Swifts.
A chart is only as good as marketing makes it. There are zero specifics to that chart meaning other than the word "Swift" there is no actual data to determine what is being measured. It could be some random Swift spring (don't know size nor rate) and a leaf spring off a 1912 Model T as brand B and that little spring off your ball point pen as brand A. You have no idea. They aren't even willing to compare against a major brand like Eibach and compare competing products. It is pure marketing, pure gimmick. I have nothing against Swift and have used their springs, but marketing is just marketing and is typically as close to flat out lying and creating bias as one can legally do.

For funzies:
http://forums.nasioc.com/forums/show....php?t=1389951

Last edited by Back Road Runner; 11-03-2013 at 09:38 PM.
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Old 11-04-2013, 07:40 AM   #20
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Quote:
Originally Posted by Back Road Runner View Post
Now we have 2" of preload force + 2" of compression due to the 1000 lbs of chassis on this spring. We end up with 3" of bump travel remaining before bottoming out the damper and 2" of droop travel. This is how preload is used.
Hi Back Road Runner, thanks for taking the time to explain. But I have some questions.

Firstly, I do not understand how you get 3" of bump travel.
2" of preload force + 2" of compression due to the 1000 lbs of chassis will compress the spring by 4", so the bump travel should be 1" before bottoming out?

Secondly, lets say we have the same 250lb/in springs and a 1000lb per corner car and following your theory above.
On the left spring, I set 0 preload.
On the right spring, I set 1" preload.
When the car's weight rests on the springs, the left spring will compress 4", right will compress 3".
So eventually both springs will be compressed by the same amount.
However, if you look at the pictures I uploaded, it is clear that the right spring has more preload and at the same time is compressed more than the left. This does not tally, as the springs should compress by the same amount. why?

I measured the height from the orange plate on the top of the spring to the bottom orange plate (near the sticker) for both coilovers, they are exactly the same.
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Old 11-04-2013, 10:32 AM   #21
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It was merely an example, not specific to your coilovers.

Yes, the chassis will apply the same total force down. All preload does is determine how far down it goes. With 0 preload, the spring will begin to compress immediately as you put chassis weight on that coilover. In your example, 1" of preload will preload the other side 250 lbs. For the first 250 lbs of loading, the other coilover will remain at full extension. It is only after the initial 250 lbs of force applied by the chassis that the coilover will begin to compress. From full extension, the first coilover would compress 4" and the second coilover will only compress 3" down from full extension. If we stay with the example of 5" of travel, you will have 1" of bump travel remaining on the first coilover and 2" of bump travel remaining on the second coilover. Now you will have an offset of ride height between both sides of 1". You can correct this with preload for the first coilover and even out suspension travel, or you can correct ride height using the ride height adjustment instead, get an even ride height, but have uneven bump/droop travel side to side which would make a messy ride.

The one part I don't know about the pictures is if the rubber dust boot slides over the threaded section of the coilover. If it does, I can't tell how far the coilover is compressed. The dust boot hides where in the travel range the coilover is resting. If the dust boot stops at the threaded section, then it appears one coilover is compressed more than the other. In this case, it isn't an issue of preload difference but a difference in weight loading, for whatever reason. The correction is then made at the ride height adjustment instead meaning it is like the example above where they end up with different remaining bump and droop travel. I don't know why it is happening though. I don't know if it's a spring rate difference (person put one front spring on the rear) or different settings at the front that affect the settings on the rear. I don't know. I'm also making an assumption of how the dust boot fits on the coilover when I say this because I don't know if it stops at the top of the threaded section or slides down over. I don't know if I can use the dust boot as an indicator of how far the shaft is pushed down. If I can, then one side is clearly pushed farther down. If I can't use the dust boot as an indicator, then I can't tell. You would really need to lift the car and unload the suspension to tell. If the suspension is unloaded in the picture, then I can make the assumption that both coilovers are fully extended in the picture and can state there is a difference in preload, although I still can't say why it was done without seeing spring rates and how all 4 corners of the car are adjusted.
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Old 11-04-2013, 11:23 AM   #22
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Quote:
Originally Posted by Back Road Runner View Post
It was merely an example, not specific to your coilovers.

Yes, the chassis will apply the same total force down. All preload does is determine how far down it goes. With 0 preload, the spring will begin to compress immediately as you put chassis weight on that coilover. In your example, 1" of preload will preload the other side 250 lbs. For the first 250 lbs of loading, the other coilover will remain at full extension. It is only after the initial 250 lbs of force applied by the chassis that the coilover will begin to compress. From full extension, the first coilover would compress 4" and the second coilover will only compress 3" down from full extension. If we stay with the example of 5" of travel, you will have 1" of bump travel remaining on the first coilover and 2" of bump travel remaining on the second coilover.
I agree with you that I still need to jack the car up and see both suspensions at full droop before making any conclusions. Tomorrow I will go to my workshop to jack it up and see.

However, I still don't understand how you get 2" of bump travel remaining on the second coilover.
The second coilover will compress 3" + 1"(preload amount) = 4". So with the car loaded on the springs, both springs will be compressed to 4", and left with 1" of bump travel. Am I missing something here?

Quote:
Originally Posted by Back Road Runner View Post
Now you will have an offset of ride height between both sides of 1". You can correct this with preload for the first coilover and even out suspension travel, or you can correct ride height using the ride height adjustment instead, get an even ride height, but have uneven bump/droop travel side to side which would make a messy ride.
Why will there be an offset of ride height of 1"? Both springs are compressed to 4". Also, for this coilover, adjusting preload will not intefere with ride height, you just need to screw the spring perch while the coilover height remains the same?
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Old 11-04-2013, 01:19 PM   #23
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The preload resists compression. This may be a matter of defining what stroke range I'm talking about. When I say 5" of travel, I'm referring to the damper, not the spring. This spring will have its own amount of travel too before full compression, so there is a concern there also, but I'm ignoring that in the example. The confusion may have to do with me talking about damper travel and you talking about spring travel.

Same example but lets add spring travel as well:
1000 lbs applied on a 250 lb/in spring, damper stroke = 5", spring stroke = 5"

For 1000 lbs, we both agree that a 250 lb/in spring will compress 4". Preload or not, the spring will compress a total of 4" from full extension. You are correct about that.

Preload will affect the damper stroke. With zero preload, the piston will move in 4", leaving only 1" of remaining travel. If we add 1" of preload to the spring, we will precompress the spring but resist the first 250 lbs of force before the damper piston moves. Under full load, the piston will only move in 3" due to preloading the spring. We end up with 2" of remaining damper travel. This is what preloading gains us, more bump travel, at least in the damper.

Now we do need to consider both the spring and damper range of motion when figuring out how much travel we have left. In the above example, the preload gave us 1" more inch of bump travel in the damper, but unless the spring can compress 2" more inches, it doesn't gain us anything. In the above example, the spring only has 5" too meaning we will end up with coil bind in 1" more inch of compression. In this case we are spring limited for travel, not damper, and adding preload doesn't help us. The only good choices from this point is to (a) use a longer spring that has a stroke of 6" like using a 10" spring instead of an 8" spring or (b) use a stiffer spring that allows us to get the same desired position without preload. If we went to a 333 lb/in spring and used zero preload, both the spring and damper would only compress 3", the same damper position as the 250 lb/in spring with 1" of preload.

That probably clears up the confusion. I was strictly referring to the damper, not the spring when discussing range of travel. We really do need to split the two and consider the two when designing and setting a coilover package.
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Old 11-05-2013, 12:35 AM   #24
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Ah I understand what you are referring to now, if it is damper travel yes we will get 2" of travel based on your example.

Quote:
Originally Posted by Back Road Runner View Post
For 1000 lbs, we both agree that a 250 lb/in spring will compress 4". Preload or not, the spring will compress a total of 4" from full extension. You are correct about that.
However, the theory above still don't tally with what I am seeing in the pictures.
Preload or not, the springs should compress by the same amount.
But in the pictures, clearly the right spring is more compressed, which lead me to think that using your example above, preload or not both springs will still compress by 4", the right spring will compress a total of 5" (1" preload), leaving it more compressed than the left spring.
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