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kerrys914

GC 280Z is now too low.

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Let me know if this is right.

 

Once the threaded collar nut reaches the point of zero (0) spring preload, the collar nut position no longer raises the car any higher by raising the collar nuts position (compressing the spring). The opposite is also true, the only way a car is lowered is to have the threaded collar nut below the point of zero (0) spring preload.

 

To add more height (after zero preload is reached) the top mounting point of the strut (where it attaches to the car) needs to be changed by adding a spacer or other means.

 

Thanks and I hope I am explaining this well..

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Think of it this way:

 

If you set the coil-over so that the collar just takes all of the slack out of the spring (zero pre-load), the spring will compress enough to support the weight of the car when installed. For the sake of example assume 250 lb springs, no pre-load, 600 lbs on the corner, and a motion ratio of 1.  When installed and the car is resting on the tires, the spring will compress 600/250 in (2.4 inches).

 

Now, if you pre-load the spring before installing it by turning the adjuster collar up one inch, the spring will be pre-loaded by 250 lbs.  Once installed, you would have to apply 250 lbs to the strut before it begins to compress.   With the same 600 lbs on the corner, the car will now only compress the spring an additional 1.4 inches.   The spring itself will still be compressed 2.4 inches, but 1 inch of that was before installation.   The car will sit 1 inch higher at rest.

 

Now, take an extreme example.  If you pre-load the spring 2.4 inches, then you would have 600 lbs of preload.  When installed on the car, the suspension would not compress at all under static conditions.  You would have raised the car 2.4 inches above the zero pre-load condition.

 

When I ran the 250 lb springs on my car, I ran a slight preload (somewhere around an inch).  Pre-loading the springs using the collars isn't easy unless you have bearings between the springs and the collar.  Do yourself a favor and install these between the spring and collar.

 

http://www.speedwaymotors.com/QA1-7888-109-Coil-Over-Thrust-Bearing-Kit,6001.html

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Thanks guys. I guess the part I am getting confused on is  this:

 

It seems like adding preload doesn't raise the car up at rest. It just compresses the spring before the car's weight is applied. In the examples above:

 

0" of preload and 2.4" of compression due to the car's weight is 2.4" of total compression at rest

OR

1" of preload and 1.4" of compression due to the car's weight is still 2.4" of total compression at rest.

OR

2.4" of preload compression and 0" of compression due to the car's weight is still 2.4" of total compression at rest.

 

In all examples above the car's height will be the same at rest.....correct? So preload doesn't change the ride height

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Wrong.

 

Raising the collar to preload the spring will raise the car.

 

The height of the car is dependent upon the distance between the attachment of the top of the strut to the chassis and the spring collar below the spring.  For a given weight, the spring will compress the same, but if the bottom of the spring is raised then the whole car will be raised.

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Hmm I think I've had this all wrong then. I thought you had to overcome the weight of the vehicle to begin raising the car. I guess the corner of the car just needs a certain amount of force to hold it up. 

 

The 4 extremes:

250lb/in spring

500lb corner weight

 

So if you would up the collar to add pre-load equal to the weigh of that corner, when you load the suspension, that corner would not move.

500lb pre load 500lb corner weight, suspension does not compress when loadedm car does not change from droop height

 

If you wound the corner up higher with more pre-load then the weight of that corner, then the car still would not rise.

750lb pre load 500lb corner weight, suspension does not compress when loaded, car does not change from droop height

 

If you wound down the collar so the spring has no preload, then the spring and subsequent car would compress the spring until the spring held up the weight of the vehicle.

0lb pre load 500lb corner weight, suspension compresses 2 inches, car drops 2 inches

 

If you continued to wind down the collar then the car would still compress the spring the same amount, you would just loose shock travel as it will take a certain amount of height before the load reaches the spring.

0lb pre load 500lb corner weight, suspension compresses 2 inches, car drops 2 inches + the distance needed to engage the spring

 

So anything in the middle where you begin to add preload would subtract away from the height the spring has to compress.

250lb pre load 500lb corner weight, suspension compresses 1 inch, car drops 1 inch

 

Is that more correct?

Edited by seattlejester

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Correct.

 

 

I am running 500 lb/in springs on the front and have them set to essentially zero pre-load.  When the car is jacked up, the spring is just barely applying force between the lower spring seat and top hat.

 

If I were to lower the seat, the car's ride height would also be lowered.  However, the spring would now be loose when the car is raised off the ground (the spring can come off its seat).

 

It is common for people running really stiff springs to use a droop limiter to prevent the springs from becoming fully unseated when the wheels are off the ground.

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Wrong.

 

Raising the collar to preload the spring will raise the car.

 

The height of the car is dependent upon the distance between the attachment of the top of the strut to the chassis and the spring collar below the spring. For a given weight, the spring will compress the same, but if the bottom of the spring is raised then the whole car will be raised.

Doesn't this only apply to before any preload is added to the spring. I can see that.

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Doesn't this only apply to before any preload is added to the spring. I can see that.

Imagine if the spring was unobstructed by the tophat and you raised the collar 2".  The top of the spring would also be raised 2" and therefore, the car raised by two inches.  Preload doesn't change this, because the 2.4" of spring compression is from spring free length height, not from the partially compressed state it is in when preloaded.  

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Trial and error works faster than all this head scratching.

Well, that assumes that you are starting with a combination that has a prayer of giving you the results you want.  The OP isn't in this situation.  At this point for him, trial and error would mean buying random springs/collars and trying things until something works, which isn't so fast.

 

74_5.0L_Z's advice is dead on here.  If you go back to his original response, the advice of using a longer spring with the same rate was probably the easiest path to take.  I'm running 14" 140lb/in on the front of mine (I'm in Detroit and stiff suspensions don't last very long here).

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I helped to lead you astray here.

 

Namor is using a good example. 

 

This system where you only have a collar for the spring pre-load only comes into play when the spring meets resistance, this would be when the shock is fully extended, as in the same type of situation when the car is hanging in the air allowing the wheels to droop. Pre-load means exactly that, you are pre loading the spring as in you are adding load before you add the actual weight of the car. So if you can imagine if you slowly lowered this theoretical car with pre-loaded springs the car would not drop in height until the weight on the spring over came the amount of preload.

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Just to close this issue out..

 

I ended up adding 1" alum. spacers between the T3 camber plate and Z body.

 

I would recommend only cutting the rear struct .75" rather then 1.5" (which is typical) if you plan on using T3 (possibly other's) camber plates.

 

I also added spring perch/collar needle bearings to aid in the adjustment of the the collar.

 

Cheers

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On 5/2/2016 at 12:56 PM, kerrys914 said:

Just to close this issue out..

 

I ended up adding 1" alum. spacers between the T3 camber plate and Z body.

 

I would recommend only cutting the rear struct .75" rather then 1.5" (which is typical) if you plan on using T3 (possibly other's) camber plates.

 

I also added spring perch/collar needle bearings to aid in the adjustment of the the collar.

 

Cheers

I know this is an older conversation but I am about to do this.

If you do not use any camber plates would you still cut the rear struts 1.5"?


Were you happy with the 1.5" off to front? Do you get good road clearance after changing tires?

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