Spring preload to lift?

[gbub]

I have read in several threads online that lift is achieved by preloading the springs and that causes the springs to be stiffer. I may be misunderstanding but I have the Eibach Pro 2.0 coil over kit that has adjustable lift. I have not installed them yet but have been studying them to determine how preload would result in lift.

The only preload I see is at full extension of the shocks. This preload goes away once the weight of the vehicles setting on the springs. The spring height is the same with vehicle weight on it no matter what the shock full extension preload is. What is changing is the position of the bottom of the spring and that also changes the position of the top of the spring which in turn raises or lower the ride height of the vehicle.

Of course if you preloaded the spring at full shock extension to more that the load of the vehicle you could change the stiffness of the spring with the load of the vehicle on the spring. You would also have a very rough ride because the shock would be at full extension and very much reduced shock travel. I don't think anyone would design a system to do that.

So, I don't see anyway an adjustable height coil over system can ride rougher by lifting with the adjustment. That would only happen by installing stiffer springs.

If anyone has valid information that does not agree with what I determined, please let me know. I want to fully understand what I am installing on my Bronco.

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[87-Z28]

Always lots of confusion about spring preload.

1) a mechanical coil spring has an inherent stiffness based on its material and geometry. Preload does NOT affect spring stiffness.

2) preload compresses a spring a given amount and thus induces a static force within the spring. That force helps to resist the static vehicle weight thus adding lift.

 

[gbub]

You had me until 2). If you have a coil that compress to a height of 12 inches at 500 lbs load, that should not change if you preload to 250 lbs. With it not preloaded it starts at 0 lbs load at maybe 18 inches and compresses through 250 lbs and to 12 inches at 500 lbs. If you preload to 250 lbs the coil maybe at 15 inches and will not compress until you get the load up to 250 lbs. At that point it will compress to the 500 lbs and should again be at 12 inches height.

Say the vehicle weight on the coil is 500 lbs, I don't see how that preload would change the ride height because the spring height does not change. If the vehicle load is 250 lbs, the ride height would not change either, but you would have some very strange acting suspension because there would be no spring action when the vehicle force on that coil becomes less than 250 lbs in bumps.

I am not saying I think you are wrong. I just don't understand your explanation.

 

[AccuTune Offroad]

I have read in several threads online that lift is achieved by preloading the springs and that causes the springs to be stiffer. I may be misunderstanding but I have the Eibach Pro 2.0 coil over kit that has adjustable lift. I have not installed them yet but have been studying them to determine how preload would result in lift.

The only preload I see is at full extension of the shocks. This preload goes away once the weight of the vehicles setting on the springs. The spring height is the same with vehicle weight on it no matter what the shock full extension preload is. What is changing is the position of the bottom of the spring and that also changes the position of the top of the spring which in turn raises or lower the ride height of the vehicle.

Of course if you preloaded the spring at full shock extension to more that the load of the vehicle you could change the stiffness of the spring with the load of the vehicle on the spring. You would also have a very rough ride because the shock would be at full extension and very much reduced shock travel. I don't think anyone would design a system to do that.

So, I don't see anyway an adjustable height coil over system can ride rougher by lifting with the adjustment. That would only happen by installing stiffer springs.

If anyone has valid information that does not agree with what I determined, please let me know. I want to fully understand what I am installing on my Bronco.

You're on the right track. Adding preload does not change the spring rate.

Are you mostly concerned about a stiff ride after adding preload to those Eibach coilovers?

 

[Brian_B]

This is a good read too

https://tacoma3g.com/threads/spring...tes-height-preload-and-ultimately-lift.12228/

 

[87-Z28]

Spring stiffness and length are the two most critical coilover design parameters. Stiffness dictates the fundamental frequency response of the suspension. Proper length allows for sufficient preload such that static equilibrium (ride height) occurs near mid travel of the shock and the spring not to bind during full compression.

 

[gbub]

You're on the right track. Adding preload does not change the spring rate.

Are you mostly concerned about a stiff ride after adding preload to those Eibach coilovers?

I am not concerned about a stiff ride after adding preload. I am just trying to understand why some people think it does.

I am an Aerospace Engineer and spring function (stress and strain) is covered in beginning level Physics. I see nothing that would indicate this type of preload would make the spring stiffer when vehicle load is applied to it. However, being a scientist, I like to keep an open mind and try to understand something I may be overlooking.

 

[gbub]

This is a good read too

https://tacoma3g.com/threads/spring...tes-height-preload-and-ultimately-lift.12228/

That is good information, but it mainly discusses using longer springs to increase preload. That results in different spring and shock dynamics. Doing that does increase stiffness. When ride height is adjusted with an adjustable perch you don't get the advantages he speaks about with a longer spring. You also should not get a stiffer ride by adjusting preload with the adjustable perch.

 

[userdude]

If you're an engineer, @87-Z28, @Snacktime, @BigMeatsBronco and @5GENIDN might be able to answer your questions. 87-Z28 has already tried, so maybe it's not immediately clear.

 

[gbub]

Spring stiffness and length are the two most critical coilover design parameters. Stiffness dictates the fundamental frequency response of the suspension. Proper length allows for sufficient preload such that static equilibrium (ride height) occurs near mid travel of the shock and the spring not to bind during full compression.

I fully agree with that. One thing to take note of is when adjusting the perch on a coil over like Eibach Pro you could be moving the shock away from the mid travel at static ride height. I am sure Eibach and other adjustable perch coil over manufactures take that into consideration.

 

[NC_Oak]

I fully agree with that. One thing to take note of is when adjusting the perch on a coil over like Eibach Pro you could be moving the shock away from the mid travel at static ride height. I am sure Eibach and other adjustable perch coil over manufactures take that into consideration.

Hi -engineer here too, go UAB Blazers.

You're looking to understand how the eibachs or other perch collar adjustables result in lift. KISS here i think. They change the position, at load, within the coilover's stroke, but do that via that adjustment to the spring's compression. the rate of the spring doesnt change, but you've decreased it's free length, which in turn, pushes "up", as your tires aren't able to be pushed down while on solid ground.

And by the way, hurry up and put those protruck 2.0s on. I've had mine on for a couple weeks including a trail ride and I love them.

 

[5GENIDN]

That is good information, but it mainly discusses using longer springs to increase preload. That results in different spring and shock dynamics. Doing that does increase stiffness. When ride height is adjusted with an adjustable perch you don't get the advantages he speaks about with a longer spring. You also should not get a stiffer ride by adjusting preload with the adjustable perch.

Okay... I am odd so I kind of think about things differently..... I think the explanations above were excellent but I do think in more simple terms...

So... and adjustable perch, or top hat moves the entire assembly downward giving you more space between the axle and the frame........ Simple enough The dampener and the spring still have the exact same relationship. For every inch that the spring is compressed the dampener is compressed one inch. So lets say ride at neutral is at 15 inches (random number).... you articulate the axle 1 inch upward and both the dampener and the spring are in the 14 inch position.

So with preloading the spring we actually move the spring one inch but the rest of the assembly does not move. This means the the spring has moved downward relative to the assembly and the dampener actually has to extend one inch to match. The spring is still at the 15 inch position but the dampener is at the 16 inch position.

When we articulate (compress in this hypothetical) the spring is at the 14 inch position but the dampener is at the 15 inch position.... It is as if the spring has additional load on it that the dampener cannot "see". It is like the dampener thinks it has less load than the spring thinks it has. Hence the spring is "preloaded".

At least that is how I think of it... I don't know if that helps at all.

 

[NC_Oak]

Okay... I am odd so I kind of think about things differently..... I think the explanations above were excellent but I do think in more simple terms...

So... and adjustable perch, or top hat moves the entire assembly downward giving you more space between the axle and the frame........ Simple enough The dampener and the spring still have the exact same relationship. For every inch that the spring is compressed the dampener is compressed one inch. So lets say ride at neutral is at 15 inches (random number).... you articulate the axle 1 inch upward and both the dampener and the spring are in the 14 inch position.

So with preloading the spring we actually move the spring one inch but the rest of the assembly does not move. This means the the spring has moved downward relative to the assembly and the dampener actually has to extend one inch to match. The spring is still at the 15 inch position but the dampener is at the 16 inch position.

When we articulate (compress in this hypothetical) the spring is at the 14 inch position but the dampener is at the 15 inch position.... It is as if the spring has additional load on it that the dampener cannot "see". It is like the dampener thinks it has less load than the spring thinks it has. Hence the spring is "preloaded".

At least that is how I think of it... I don't know if that helps at all.

Spoken / explained like a true teacher...

 

[BigMeatsBronco]

Okay... I am odd so I kind of think about things differently..... I think the explanations above were excellent but I do think in more simple terms...

So... and adjustable perch, or top hat moves the entire assembly downward giving you more space between the axle and the frame........ Simple enough The dampener and the spring still have the exact same relationship. For every inch that the spring is compressed the dampener is compressed one inch. So lets say ride at neutral is at 15 inches (random number).... you articulate the axle 1 inch upward and both the dampener and the spring are in the 14 inch position.

So with preloading the spring we actually move the spring one inch but the rest of the assembly does not move. This means the the spring has moved downward relative to the assembly and the dampener actually has to extend one inch to match. The spring is still at the 15 inch position but the dampener is at the 16 inch position.

When we articulate (compress in this hypothetical) the spring is at the 14 inch position but the dampener is at the 15 inch position.... It is as if the spring has additional load on it that the dampener cannot "see". It is like the dampener thinks it has less load than the spring thinks it has. Hence the spring is "preloaded".

At least that is how I think of it... I don't know if that helps at all.

Excellent description. This is why I suggest the top hat spacers over the spring preloaded style lifts.

 

[dgorsett]

I'm not an engineer, but I played one at work and agree with your premise. When I installed my 5100s at full extension the springs where compressed i.e. pre loaded. Once I installed them and put the vehicle weight on them they compressed to the same point they did before the install, albeit from a higher stating point. I would think the only point they would act differently than stock is when fully extended and in a somewhat preloaded condition.

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