Coilover question - adj preload vs. adj shock body

[tigeo]

Coilover question for the suspension gurus out there.

I am trying to deal with this in my head and struggling for some reason. Some coil overs have both an adjustable shock body and adjustable pre-load. Some have adjustable pre-load only.

On the adjustable shock body coil overs, you are lengthening or shortening the overall length of the coil over – coil spring preload and damper travel are unchanged regardless of height adjustment. (right?)

For the coilovers that only have preload adjustment, you are increasing the preload to raise the car and decreasing the preload to lower the car. In this case, you are changing where in the suspension travel the starting point/resting point of the suspension is. (right?)

For the first case, I can see this being an issue for lowering too much b/c it will allow the wheel to move upward too much possibly contacting something it’s not supposed to. In the preload adjustment only case, the lower the car sits the less upward suspension travel you have before bottoming out….so just changing where in the suspension’s travel you sit (overall travel remains constant)....right? aahahaha

 

[bfury5]

Preload adjustment should really never be used to height adjust a coilover. The suspension will operate best when the preload is set per the mfg recommendation. Anything but the specified preload can affect the performance of the damper because the damper might not be utilizing all of the shaft travel and this can affect how the valving within the damper operates.

Correct on your second point. A coilover that is truly height adjustable has the ability to move the body of the damper separate from the preload. However in this scenario there are potential scenarios where the suspension can be adjusted in a way that results in contact inside the wheelwell.

Height adjustable coils are great because of their adjustability, but the tradeoff us is you usually end up with less overall travel because the shock body has to be shortened to allow for height adjustment of the coil. This is *ok* for a street car, but a racecar would have a damper that is custom built to maximize shock travel at a given ride height and damper packaging. A damper that is only preload adjustable will *usually* have more shock travel in a similar sized package. This is the preferred setup, but people usually mistake preload adjustment for true hight adjustment.

 

[tigeo]

Preload adjustment should really never be used to height adjust a coilover. The suspension will operate best when the preload is set per the mfg recommendation. Anything but the specified preload can affect the performance of the damper because the damper might not be utilizing all of the shaft travel and this can affect how the valving within the damper operates.

Correct on your second point. A coilover that is truly height adjustable has the ability to move the body of the damper separate from the preload. However in this scenario there are potential scenarios where the suspension can be adjusted in a way that results in contact inside the wheelwell.

Height adjustable coils are great because of their adjustability, but the tradeoff us is you usually end up with less overall travel because the shock body has to be shortened to allow for height adjustment of the coil. This is *ok* for a street car, but a racecar would have a damper that is custom built to maximize shock travel at a given ride height and damper packaging. A damper that is only preload adjustable will *usually* have more shock travel in a similar sized package. This is the preferred setup, but people usually mistake preload adjustment for true hight adjustment.

Thank you for that response you have clarified my questions! So the Bilstein PSS for example...only height-adjustment is through preload, no body adjustment. I suppose b/c you are only adjusting a small amount the pre-load style height adjustment should be ok? I think of all of this w/r to my mountainbike suspension and sag....you change the sag by adjusting preload.

 

[bfury5]

Thank you for that response you have clarified my questions! So the Bilstein PSS for example...only height-adjustment is through preload, no body adjustment. I suppose b/c you are only adjusting a small amount the pre-load style height adjustment should be ok? I think of all of this w/r to my mountainbike suspension and sag....you change the sag by adjusting preload.

On a MTB you do change sag by adjusting preload. Keep in mind the weight of a rider on a bike makes up a HUGE portion of the total bike+person combo that the suspension has to control. Different rider means totally different weight, so there's a need for a large range of adjustments. In a car, sag is just the vehicle at rest. That shouldn't change too much on a case-by-case basis. Small changes in preload to adjust height, akin to corner balancing, would be okay.

 

[tigeo]

On a MTB you do change sag by adjusting preload. Keep in mind the weight of a rider on a bike makes up a HUGE portion of the total bike+person combo that the suspension has to control. Different rider means totally different weight, so there's a need for a large range of adjustments. In a car, sag is just the vehicle at rest. That shouldn't change too much on a case-by-case basis. Small changes in preload to adjust height, akin to corner balancing, would be okay.

And I suppose that's it then - it's really small adjustments in the preload to change the height on coils like the Bilsteins - they don't slam the car down.

 

[Gvazquez]

The most race oriented coilovers dont have adjustable shock bodies. Mainly because moving the spring perch does not affect the springs performance because these said coilovers also use linear springs that don't change rates as they're compressed. On a progressive spring, moving the spring perch to adjust ride height would be bad because now you've change the static spring rate.