explain preload.....too little or too much?
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OG triple OG
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From: Norcal
explain preload.....too little or too much?
im curious . can a damper be preloaded too muh? should you just get the gap out of the coil and the bottom of the shock tower , or should you put a certian amount of pressure ?
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From: sheboygan, wi, 53081
Re: explain preload.....too little or too much? (Hella_JDM)
this is a good question; one i'm still trying to understand myself. what do you have going on with your suspension soo far? what kinda spring are you referring to, like an oem spring or a progressive? i have illumina/gc with gc upper mounts. my car is daily driven so i went with whatever spring rates they come stock with. i figured this setup would ride just slightly dropped, and the springs would be under load even with the wheels off the ground, ya know like an oem shock/spring combo. not so the case....it seemed that for the springs to be loaded, the ***-end was way up in the air (at least stock height). by spinning the perch down, it's at the right height but no spring preload...which is where i think i was getting the bouncy rear-end (not real bouncy but enough to be uncomfortable). soo after doing alot of reading, i decided to take my stock shock upper-mounts and lengthen them prolly another 3+ inches; i did this to take up the space between the spring and the perch. get it all together and take it for a ride.....there's definately no bounce, but it's even more harsh than before. kinda like the car doesn't move up and down over bumps, but i'm bouncing up and down in my seat....really sucks. this is all with my illuminas set at like full soft or one step up from full soft. now all i can say is that lengthening the upper mount put the springs in a preload situation, but the shock is like fully extended, and seems to have less travel, or at least where its now traveling. my next step was ordering a set of 2" LONGER eibach 280lb. springs, putting the gc mounts back on....the longer springs should take up the space, allow me to preload the springs, and get a little extra travel. i'm crossing my fingers here but i've tried many other combinations and they haven't given me the results i'm looking for yet. i'm pretty sure to have a decent ride on the street, there's gotta be decent travel involved.
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OG triple OG
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From: Norcal
Re: explain preload.....too little or too much? (loodood)
i have tein flex's which have adjustable preload. im just wondering how to do it properly, i also want to corner weigh the car to get the suspension in tune, its just like a motor , a properly tuned suspension will perform much better ie. balanced tires , balanced corners on the car etc......
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From: Off THE 60, Between THE 605 and THE 57
Re: explain preload.....too little or too much? (Solracer)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Solracer »</TD></TR><TR><TD CLASS="quote">Preload is really only usefull to keep the spring seated when the suspension is fully extended.</TD></TR></TABLE>
Apparently Tein markets the flex as being spring rate adjustable via preload. Which, i guess makes sense if they're using progressive springs...
but yes, sol racer is right.
Like the sig! looks like i missed an awesome brake rotor argument
Apparently Tein markets the flex as being spring rate adjustable via preload. Which, i guess makes sense if they're using progressive springs...
but yes, sol racer is right.
Like the sig! looks like i missed an awesome brake rotor argument
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Re: explain preload.....too little or too much? (bad-monkey)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bad-monkey »</TD></TR><TR><TD CLASS="quote">
like the sig! looks like i missed an awesome brake rotor argument</TD></TR></TABLE>
It was a couple of months ago... but I have not found a new quote of the week... maybe "Buy Omni they'll get it right eventually"
like the sig! looks like i missed an awesome brake rotor argument
</TD></TR></TABLE>It was a couple of months ago... but I have not found a new quote of the week... maybe "Buy Omni they'll get it right eventually"
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OG triple OG
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From: Norcal
Re: explain preload.....too little or too much? (Solracer)
so for preload all you need to do is take the slack out of the coil? is screwing it further bad? i asume that changes the rate of the spring....
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From: I am Tyson
Re: explain preload.....too little or too much? (Hella_JDM)
i dont think you could possibly preload a spring too much. theres really no reason to preload it excessively. also, you dont even need any preload. omnipower will tell you that their coilovers require some preload. they also blindly copy other ppls designs and offer free replacements when they mess up. so what do they know?
one misconception about preload is that it changes the spring rate, or makes the spring stiffer. absolutely not. if the spring is linear, the spring rate SHOULD remain the same, no matter the amount it is initially compressed. (not all springs are equal, some of the crappy taiwanese springs have exhibited non-linear behavior when they clearly were not designed to)
the truth is, your cars weight determines the amount of static preload. by that i mean, when all 4 wheels are rested on the ground. on a 2400lb car, say weight is equally distributed at all 4 corners, 600lbs over one wheel. theres not much you can ever do to change this, youd have to physically move stuff (battery, add ballasts) to change the weight distribution, so lets call that constant.
say you used an adjustable spring kit like ground control and had set the spring perch to just a BIT of preload, just so that the lower collar is touching the spring and no more. and say its a 300lbs/inch spring rate on that spring. jack the car up in the air and slowly let it drop, the car will drop 2" from the point the wheel touches the ground. lets say the bottom of the car is 5" from the ground.
now raise that spring perch from the point of nearly zero preload to 1" higher. you put 300lbs of pressure on that spring already. the wheel is probably going to be a bit more than 1" higher now, relative to the chassis because the spring to ride (wheel) height ratio is more like 1:1.5, but lets assume 1:1 here. drop the car onto the ground, and measure. the weight of the car is STILL going to push down on the spring the extra inch, until it reaches 600lbs of weight. the spring is still going to compress 2" and the car is now going to be 6" from the ground. youve raise the car 1" with one other change...
what has changed is whats called droop or sag. the distance the wheel can extend has been limited. now instead of having to raise the car 2" off the ground until the wheel is fully in the air, its just 1". what i do know from motorcycle backgrounds, motorcycles are VERY sensitive to sag distances. but i never really hear it talked about it for cars, so im just gonna figure its not really important and chalk it up as the difference between riding on 2 wheels instead of 4. quite frankly, i dont think you can even put enough pressure on that collar to provide any more than 300lbs anyway. so its quite moot to wonder what happens if you preloaded it 2", which would be 600lbs. then things get really funky. you basically at that point have no droop even though the ride height has NOT CHANGED. but like i said, the point is moot because youll never get there.
now, lets go the OPPOSITE direction. from the point of almost zero preload, lower the collar 1". there is now NO preload and the spring can even move around once the side is jacked up. drop the car again and youll find the ride height has finally changed, and its now lowered 1" with 4" from the bottom of the car to the ground. lower the perch 2", the ride height lowers 2". spring rate has since remained the same as well.
so basically, PRELOAD IS POINTLESS. let me remind you, this goes for adjustable spring kits, sleeve type, like ground controls. the spring should be free and rattling in order to adjust ride height. its very normal. the down side to lowering the spring perch is directly reducing the amount of shock travel. say you lower it 2", youve lost 2" of shock travel, with only perhaps a total of 5" until you hit the bumpstop. you can do other things like extend the top shock mounting point (like GC extended top hats, or just custom shortening your shock which only really koni does for a good price)
on the subject of threaded body shocks with adjustable lower cups, yes, those types of coilovers can (should) independently change ride height to shock travel. id have to say thats a nice thing about the full threaded body coilover setup. but in the case of poorly designed full coilovers, like omnipowers kit for the CRX and EF, the lower cup doesnt even allow any adjustment before it bottoms out. so basically to lower it any decent amount, you have to rely on the spring perch, basically removing any preload and again directly taking away from shock travel. the one benefit of that setup is completely wasted. yeah yeah, tehy got a "fix" for that, "contact your omnipower supplier" or "its coming out next month". when arent they fixing their crap....
in summary, dont worry about preload. it really doesnt mean anything relevent or affect much. you couldnt possibly have TOO much preload, and its fine or even proper to have none.
one misconception about preload is that it changes the spring rate, or makes the spring stiffer. absolutely not. if the spring is linear, the spring rate SHOULD remain the same, no matter the amount it is initially compressed. (not all springs are equal, some of the crappy taiwanese springs have exhibited non-linear behavior when they clearly were not designed to)
the truth is, your cars weight determines the amount of static preload. by that i mean, when all 4 wheels are rested on the ground. on a 2400lb car, say weight is equally distributed at all 4 corners, 600lbs over one wheel. theres not much you can ever do to change this, youd have to physically move stuff (battery, add ballasts) to change the weight distribution, so lets call that constant.
say you used an adjustable spring kit like ground control and had set the spring perch to just a BIT of preload, just so that the lower collar is touching the spring and no more. and say its a 300lbs/inch spring rate on that spring. jack the car up in the air and slowly let it drop, the car will drop 2" from the point the wheel touches the ground. lets say the bottom of the car is 5" from the ground.
now raise that spring perch from the point of nearly zero preload to 1" higher. you put 300lbs of pressure on that spring already. the wheel is probably going to be a bit more than 1" higher now, relative to the chassis because the spring to ride (wheel) height ratio is more like 1:1.5, but lets assume 1:1 here. drop the car onto the ground, and measure. the weight of the car is STILL going to push down on the spring the extra inch, until it reaches 600lbs of weight. the spring is still going to compress 2" and the car is now going to be 6" from the ground. youve raise the car 1" with one other change...
what has changed is whats called droop or sag. the distance the wheel can extend has been limited. now instead of having to raise the car 2" off the ground until the wheel is fully in the air, its just 1". what i do know from motorcycle backgrounds, motorcycles are VERY sensitive to sag distances. but i never really hear it talked about it for cars, so im just gonna figure its not really important and chalk it up as the difference between riding on 2 wheels instead of 4. quite frankly, i dont think you can even put enough pressure on that collar to provide any more than 300lbs anyway. so its quite moot to wonder what happens if you preloaded it 2", which would be 600lbs. then things get really funky. you basically at that point have no droop even though the ride height has NOT CHANGED. but like i said, the point is moot because youll never get there.
now, lets go the OPPOSITE direction. from the point of almost zero preload, lower the collar 1". there is now NO preload and the spring can even move around once the side is jacked up. drop the car again and youll find the ride height has finally changed, and its now lowered 1" with 4" from the bottom of the car to the ground. lower the perch 2", the ride height lowers 2". spring rate has since remained the same as well.
so basically, PRELOAD IS POINTLESS. let me remind you, this goes for adjustable spring kits, sleeve type, like ground controls. the spring should be free and rattling in order to adjust ride height. its very normal. the down side to lowering the spring perch is directly reducing the amount of shock travel. say you lower it 2", youve lost 2" of shock travel, with only perhaps a total of 5" until you hit the bumpstop. you can do other things like extend the top shock mounting point (like GC extended top hats, or just custom shortening your shock which only really koni does for a good price)
on the subject of threaded body shocks with adjustable lower cups, yes, those types of coilovers can (should) independently change ride height to shock travel. id have to say thats a nice thing about the full threaded body coilover setup. but in the case of poorly designed full coilovers, like omnipowers kit for the CRX and EF, the lower cup doesnt even allow any adjustment before it bottoms out. so basically to lower it any decent amount, you have to rely on the spring perch, basically removing any preload and again directly taking away from shock travel. the one benefit of that setup is completely wasted. yeah yeah, tehy got a "fix" for that, "contact your omnipower supplier" or "its coming out next month". when arent they fixing their crap....
in summary, dont worry about preload. it really doesnt mean anything relevent or affect much. you couldnt possibly have TOO much preload, and its fine or even proper to have none.
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OG triple OG
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From: Norcal
Re: explain preload.....too little or too much? (Solracer)
thanks for the writeup tyson. i was more concered with preload on a full bodied threaded coilover with pillowball mounts . as you cant really preload a sleeved coilover. i just wasnt sure if it would make the spring rate change or make less usefull travel or anything like that . tyson answered it for me thanks again.
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From: I am Tyson
Re: explain preload.....too little or too much? (Hella_JDM)
well, what i do find interesting is that omnipower says that you MUST preload your springs using their coilovers. well, thats great, so why are they selling adjustable spring kits "sleeve overs"? its obviously not intended to preload the spring and offer any decent amount of height adjustment. whats with the inconsistency?
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From: I am Tyson
Re: explain preload.....too little or too much? (Tyson)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson »</TD></TR><TR><TD CLASS="quote">the truth is, your cars weight determines the amount of static preload. by that i mean, when all 4 wheels are rested on the ground. on a 2400lb car, say weight is equally distributed at all 4 corners, 600lbs over one wheel. theres not much you can ever do to change this, youd have to physically move stuff (battery, add ballasts) to change the weight distribution, so lets call that constant. </TD></TR></TABLE>
i take this statement back. this obviously disregards corner weighing procedures. but that doesnt change the issue of preload.
i take this statement back. this obviously disregards corner weighing procedures. but that doesnt change the issue of preload.
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From: SoCal, CA, USA
Re: explain preload.....too little or too much? (Tyson)
Good reply tyson, but there is a point to preload on coilovers that have adjustable bodies, like the Omni's, Tein Flex, etc. And that is shock travel.
basically, you want to run enough preload so that you have adequate shock travel. using Tyson's example from above, if you preload the springs one inch, the car will sit higher by one inch than the previous unloaded setup. At the same time, you have just gained one inch of shock travel as well, since the shock rod now extends up an additional inch from the top of the shock body than previous. This is a good thing.
However, you don't want to preload the spring so much that you have no droop at all, because that's when funky things start happining with the effective spring rate and also limits how much your suspension is allowed to move.
The stiffer the spring, the less total preload you will need to maintain good shock travel, and prevent the shock from bottoming out. so you would want to preload your springs first, be it one inch or 1.5, etc. and then, use the lower mounting collars to adjust your ride height.
and like Tyson said, there is a lot of info about preload in the motorcycle world. REading a few articles helped me understand it better.
basically, you want to run enough preload so that you have adequate shock travel. using Tyson's example from above, if you preload the springs one inch, the car will sit higher by one inch than the previous unloaded setup. At the same time, you have just gained one inch of shock travel as well, since the shock rod now extends up an additional inch from the top of the shock body than previous. This is a good thing.
However, you don't want to preload the spring so much that you have no droop at all, because that's when funky things start happining with the effective spring rate and also limits how much your suspension is allowed to move.
The stiffer the spring, the less total preload you will need to maintain good shock travel, and prevent the shock from bottoming out. so you would want to preload your springs first, be it one inch or 1.5, etc. and then, use the lower mounting collars to adjust your ride height.
and like Tyson said, there is a lot of info about preload in the motorcycle world. REading a few articles helped me understand it better.
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From: cali
Re: explain preload.....too little or too much? (mike-y)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike-y »</TD></TR><TR><TD CLASS="quote">Good reply tyson, but there is a point to preload on coilovers that have adjustable bodies, like the Omni's, Tein Flex, etc. And that is shock travel.
.</TD></TR></TABLE>
that is not a reason for pre-load though, the creators of the damper, make a damper that has very limited travel, how do they make sure the consumer doesn't bottom it out? they say "pre-load" the springs.
IMO preload on those coilovers is there just becuase the damper has a very very short range of movment, from full extention to bottom'd out.
.</TD></TR></TABLE>
that is not a reason for pre-load though, the creators of the damper, make a damper that has very limited travel, how do they make sure the consumer doesn't bottom it out? they say "pre-load" the springs.
IMO preload on those coilovers is there just becuase the damper has a very very short range of movment, from full extention to bottom'd out.
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From: I am Tyson
Re: explain preload.....too little or too much? (mike-y)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike-y »</TD></TR><TR><TD CLASS="quote">Good reply tyson, but there is a point to preload on coilovers that have adjustable bodies, like the Omni's, Tein Flex, etc. And that is shock travel.</TD></TR></TABLE>
i already made that point anyway. too bad omni isnt even designed properly for this...
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson »</TD></TR><TR><TD CLASS="quote">on the subject of threaded body shocks with adjustable lower cups, yes, those types of coilovers can (should) independently change ride height to shock travel. id have to say thats a nice thing about the full threaded body coilover setup. but in the case of poorly designed full coilovers, like omnipowers kit for the CRX and EF, the lower cup doesnt even allow any adjustment before it bottoms out. so basically to lower it any decent amount, you have to rely on the spring perch, basically removing any preload and again directly taking away from shock travel. the one benefit of that setup is completely wasted. yeah yeah, tehy got a "fix" for that, "contact your omnipower supplier" or "its coming out next month". when arent they fixing their crap....</TD></TR></TABLE>
i already made that point anyway. too bad omni isnt even designed properly for this...
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson »</TD></TR><TR><TD CLASS="quote">on the subject of threaded body shocks with adjustable lower cups, yes, those types of coilovers can (should) independently change ride height to shock travel. id have to say thats a nice thing about the full threaded body coilover setup. but in the case of poorly designed full coilovers, like omnipowers kit for the CRX and EF, the lower cup doesnt even allow any adjustment before it bottoms out. so basically to lower it any decent amount, you have to rely on the spring perch, basically removing any preload and again directly taking away from shock travel. the one benefit of that setup is completely wasted. yeah yeah, tehy got a "fix" for that, "contact your omnipower supplier" or "its coming out next month". when arent they fixing their crap....</TD></TR></TABLE>
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From: SoCal, CA, USA
Re: explain preload.....too little or too much? (slammed_93_hatch)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch »</TD></TR><TR><TD CLASS="quote">that is not a reason for pre-load though, the creators of the damper, make a damper that has very limited travel, how do they make sure the consumer doesn't bottom it out? they say "pre-load" the springs.
IMO preload on those coilovers is there just becuase the damper has a very very short range of movment, from full extention to bottom'd out.</TD></TR></TABLE>
I think we just said the exact same thing, that preloading can increase the damper's range of movement.
I've never dealt with Omni's shocks, so I did not realize they weren't designed properly for this, but I have used the Tein Flex, and did have to preload the springs and then use the lower mount to adjust ride height to keep the shock from bottoming on certain corners.
IMO preload on those coilovers is there just becuase the damper has a very very short range of movment, from full extention to bottom'd out.</TD></TR></TABLE>
I think we just said the exact same thing, that preloading can increase the damper's range of movement.
I've never dealt with Omni's shocks, so I did not realize they weren't designed properly for this, but I have used the Tein Flex, and did have to preload the springs and then use the lower mount to adjust ride height to keep the shock from bottoming on certain corners.
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From: Jasma
Re: explain preload.....too little or too much? (mike-y)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike-y »</TD></TR><TR><TD CLASS="quote">I think we just said the exact same thing, that preloading can increase the damper's range of movement.
</TD></TR></TABLE>
It doesn't, the range stays exactly the same. If you increase the travel in bump you're decreasing it in rebound, no free lunch here.
</TD></TR></TABLE>
It doesn't, the range stays exactly the same. If you increase the travel in bump you're decreasing it in rebound, no free lunch here.
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Re: explain preload.....too little or too much? (El Pollo Diablo)
Im gonna piggyback off this thread hope you guys dont mind.
Does anyone here know anybody with a Tein type flex coinlover setup on an ITR?
If so can you get me the dimentions for the settings they used. Maximum of 2" drop, so I can use it as a baseline on my car. Any help would be appreciated, Thanx
Does anyone here know anybody with a Tein type flex coinlover setup on an ITR?
If so can you get me the dimentions for the settings they used. Maximum of 2" drop, so I can use it as a baseline on my car. Any help would be appreciated, Thanx
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From: I am Tyson
Re: explain preload.....too little or too much? (Valjoker)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Valjoker »</TD></TR><TR><TD CLASS="quote">Im gonna piggyback off this thread hope you guys dont mind.
Does anyone here know anybody with a Tein type flex coinlover setup on an ITR?
If so can you get me the dimentions for the settings they used. Maximum of 2" drop, so I can use it as a baseline on my car. Any help would be appreciated, Thanx </TD></TR></TABLE>
please start your own thread. thanks.
Does anyone here know anybody with a Tein type flex coinlover setup on an ITR?
If so can you get me the dimentions for the settings they used. Maximum of 2" drop, so I can use it as a baseline on my car. Any help would be appreciated, Thanx
</TD></TR></TABLE>please start your own thread. thanks.
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From: SoCal, CA, USA
Re: explain preload.....too little or too much? (El Pollo Diablo)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by El Pollo Diablo »</TD></TR><TR><TD CLASS="quote">It doesn't, the range stays exactly the same. If you increase the travel in bump you're decreasing it in rebound, no free lunch here.</TD></TR></TABLE>
ahh, very true.. I guess you'll have to decide how much of bump vs. rebound you need when setting up one of these types of coilovers. Makes me glad I ended up with konis. seems to be so much easier to setup.
ahh, very true.. I guess you'll have to decide how much of bump vs. rebound you need when setting up one of these types of coilovers. Makes me glad I ended up with konis. seems to be so much easier to setup.
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From: cali
Re: (ohjolt2)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ohjolt2 »</TD></TR><TR><TD CLASS="quote">Whats the stroke diffrence from an OTS koni to an omni? Has any one with an omni suspension ever even cared enought to measure?</TD></TR></TABLE>
i doubt any body has, but i be willing to bet that the range is in the 3 to 4 inch range, thats it.
i doubt any body has, but i be willing to bet that the range is in the 3 to 4 inch range, thats it.
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Re: explain preload.....too little or too much? (Hella_JDM)
Sorry to bring this back up, but I was looking for some info on spring preload and this thread cought my interest.
The spring might be linear, but the correlation changes under preload.
The following diagram shows a 0.5kg/mm spring. With 35mm preload, and no preload:
With 35mm preload, the spring needs +17.5kg to efectively compress (further).
Whearas with no preload, and a 17.5kg load put on the spring, it will compress 32.5mm.
So adding preload seems to increas (overall) stifness (of the suspension). Or am I misinterpreting this?
Damper travel is not compromised, but spring travel is, and there is a more force applied to the spring 's locking nut. (if my assumptions are correct).
...
one misconception about preload is that it changes the spring rate, or makes the spring stiffer. absolutely not. if the spring is linear, the spring rate SHOULD remain the same, no matter the amount it is initially compressed. (not all springs are equal, some of the crappy taiwanese springs have exhibited non-linear behavior when they clearly were not designed to)
...
one misconception about preload is that it changes the spring rate, or makes the spring stiffer. absolutely not. if the spring is linear, the spring rate SHOULD remain the same, no matter the amount it is initially compressed. (not all springs are equal, some of the crappy taiwanese springs have exhibited non-linear behavior when they clearly were not designed to)
...
The following diagram shows a 0.5kg/mm spring. With 35mm preload, and no preload:
With 35mm preload, the spring needs +17.5kg to efectively compress (further).
Whearas with no preload, and a 17.5kg load put on the spring, it will compress 32.5mm.
So adding preload seems to increas (overall) stifness (of the suspension). Or am I misinterpreting this?
Damper travel is not compromised, but spring travel is, and there is a more force applied to the spring 's locking nut. (if my assumptions are correct).
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From: Nowhere and Everywhere
Re: explain preload.....too little or too much? (Hella_JDM)
Sorry to bring this back up, but I was looking for some info on spring preload and this thread cought my interest.
The spring might be linear, but the correlation changes under preload.
The following diagram shows a 0.5kg/mm spring. With 35mm preload, and no preload:
With 35mm preload, the spring needs +17.5kg to efectively compress (further).
Whearas with no preload, and a 17.5kg load put on the spring, it will compress 32.5mm.
So adding preload seems to increas (overall) stifness (of the suspension). Or am I misinterpreting this?
Damper travel is not compromised, but spring travel is, and there is a more force applied to the spring 's locking nut. (if my assumptions are correct).
The spring might be linear, but the correlation changes under preload.
The following diagram shows a 0.5kg/mm spring. With 35mm preload, and no preload:
With 35mm preload, the spring needs +17.5kg to efectively compress (further).
Whearas with no preload, and a 17.5kg load put on the spring, it will compress 32.5mm.
So adding preload seems to increas (overall) stifness (of the suspension). Or am I misinterpreting this?
Damper travel is not compromised, but spring travel is, and there is a more force applied to the spring 's locking nut. (if my assumptions are correct).
A 35mm (17.5 kg) preload means that you could place 17.5 kg on the spring without the spring moving. But it's still compressed 35mm from its original length. Up the weight to 35kg (add another 17.5) and the spring will compress another 35mm, for a total spring delta of 70mm, so the spring rate is still 0.5 kg/mm. It would be the same if the spring had no preload on it.
This is what Tyson was talking about with the weight of the car on the suspension, preload makes ZERO difference in spring characteristics.
The graph you posted merely moves the force/compression plot to the left. The travel shown for a given force on the preloaded spring plot is relative to the preloaded spring length. Free spring length for a given force will always be the same no matter what the preload is, assuming you're talking about a force higher than the preload (which is always the case on car suspension). If the applied force is less than the preload, then of course the spring doesn't move at all.