New 5100s

Here we go again. The spring compressor is to apply the preload. The static weight of the vehicle is different than the preload. Also, a spring compressor isn't required to assemble the coilover. I have a spring compressor and didn't use it to install the 5100's on my 2023 Taco.... I used the weight of the truck to compress the spring.... it felt like cheating compared to using the spring compressor.

 

I guess i’ll never get understand the 5100’s physics lmao

 

I went 2" on my 5100's with 1" rear block. No OEM brake dive, NO regrets....

 

It used to really baffle me too. At some point the light bulb came on. What's hard to understand is that just because the preload has more compression, it doesn't mean the springs are more compressed once the weight of the vehicle is sitting on the springs. The truck weight will compress the spring the same amount no matter what notch it's sitting on. I'm no expert but this is my understanding.

Also, when a truck is lifted, it's closer to the top of the suspension travel. This can cause bottoming out at the top of the travel but can be overcome by progressive bumpstops. I haven't experienced this.... but have read this.

 

As someone who was totally confused by this before and after a bunch of research finally figured it out, more or less, let me try and explain. This comes up a lot because there is a lot misunderstanding and even misuse of language that just adds to the confusion. I'm not claiming to be an expert here. Just trying to help explain why the spring under the weight of the truck is the same regardless of which perch you use.

First, keep in mind that the strut assembly off the truck isn't the same as on the truck because when you put the weight of the truck on it the spring will compress under that weight even more than the off the truck assembly length. It has to otherwise you would be at full extension of the shock and that would be bad. How much it compresses is a function of the spring itself and the amount of weight. You can observe this when you change a tire. As you raise the truck with a jack the truck goes up for a bit before the wheel lifts. This is the spring expanding as less and less weight is compressing it. Eventually you reach full extension of the shock and then the wheel lifts off the ground. One of the videos posted earlier shows this pretty well as he demonstrates articulation.

The shock has a certain amount of travel. Let's say 10". I'm making up numbers a bit for simplicity but someone can measure this all if they want better numbers. Of that 10" of travel some is compression and some extension. When you are changing the tire you are going to fully extend it. Likewise, when assembling the strut the shock will be fully extended.

So off the truck the spring is going to fully extend the shock. It can only go so far. Let's say it extended 5" when the weight of the truck is removed. This could be the lowest setting of the 5100. Now, if we move the perch up 2" the shock might only extend 3". Many people will point out here that this "pre-load" means the spring is more compressed leading to a harsher ride. However, it's not on the truck yet. When on the truck under weight the spring will compress even more and in fact back to the exact same length as before because the weight of the truck didn't change and we are using the same spring.

What has changed is how much travel we have in the shock. Before, we had 5" before full extension. Now we only have 3". This is the limit of the shock.