Bilstein 6112 spring preload question

[awerking]

2019 TRD Off Road Non-KDSS

Getting ready to lift - heavily leaning toward Bilstein 6112/5160. Adding a front hybrid bumper and winch so going with the 650lb springs up front. Going to keep stock rear springs for a bit until I get my rear bumper at which time I'll upgrade to heavy load springs out back.

Question - to correct driver's side lean, some recommend offsetting the spring preload (i.e. drivers side circlip on the top setting and passenger side circlip two notches down to get an even 2.5" lift on both sides). I'd prefer to have the same spring preload on both sides, so how big of a spacer will I need? I've seen recommendations that range from 10mm and up, so I'm not sure which to get.

Thanks in advance for the help.

 

[4Person]

I just did the 6112s on my 15LE last weekend. I decided to go with both at the #5 perch and add a 3/8” (~10mm) spacer on the drivers side. My reasoning was that it was easier and less expensive to add or subtract spacers rather than disassemble and reassemble the struts and springs to adjust.

The good news is that I’m sitting level side-to-side.

The bad news is that I only ended up getting about 1.75” of lift on the #5 setting. I only had the 600# springs though.

 

[Muff Muff]

From a physics standpoint, having your struts set with a different preload is effectively going to make the more compressed side stiffer than the longer, less compressed side. It's not something I've ever done it practice, but I also wouldn't think that it'd be advisable if having a level ride is your only goal. When it comes to vehicle dynamics, having everything equal and balanced is key.

 

[dezertbomber]

From a physics standpoint, having your struts set with a different preload is effectively going to make the more compressed side stiffer than the longer, less compressed side. It's not something I've ever done it practice, but I also wouldn't think that it'd be advisable if having a level ride is your only goal. When it comes to vehicle dynamics, having everything equal and balanced is key.

It's the same spring rate so since these have single/linear rate springs it does not change the stiffness regardless of spring positioning (would be a different story if progressive/dual rate springs). If the suspension were to let the coils bind during compression then that's where an imbalance could occur, but that does not happen that I've experienced.

I have the 6112 7/5 650lb springs up front (stock bumper) and did a 2,000+ mile San Diego to Moab and back trip recently; feels the same on both sides. (I'm not running either sway bar so the effect would be even more exaggerated if the stiffness were different between sides.)

I have HD 2" springs in the back and the 5160's do not have enough rebound dampening valved, and leads to a sloppy feel when loaded. Unloaded, it's stiff, but smooth.

 

[TEujunga]

From a physics standpoint, having your struts set with a different preload is effectively going to make the more compressed side stiffer than the longer, less compressed side. It's not something I've ever done it practice, but I also wouldn't think that it'd be advisable if having a level ride is your only goal. When it comes to vehicle dynamics, having everything equal and balanced is key.

Ah, the "pre-load myth" lives on - and justified as "physics," no less! Back to class with you, sir!

The amount you compress the spring to fit it into the coilover assembly prior to installation is irrelevant. It does not change the spring rate. With the weight of the truck resting on the spring, it will be compressed the same amount no matter how much "pre-load" was placed on it at installation.

Increasing the "pre-load" in effect simply moves the position of the lower spring perch upward. Being that the compressed spring will be the same height under the same load, the overall height of the truck is raised as a result. Has nothing to do with any increased "stiffness" of the spring.

Leveling by adding spacers or by increasing the "pre-load" accomplishes exactly the same thing -- it just moves the effective position of the lower spring perch on one side of the vehicle in relation to the other.

Edit: Dezertbomber beat me to the punch!

 

[Muff Muff]

Ah, the "pre-load myth" lives on - and justified as "physics," no less! Back to class with you, sir!

The amount you compress the spring to fit it into the coilover assembly prior to installation is irrelevant. It does not change the spring rate. With the weight of the truck resting on the spring, it will be compressed the same amount no matter how much "pre-load" was placed on it at installation.

Increasing the "pre-load" in effect simply moves the position of the lower spring perch upward. Being that the compressed spring will be the same height under the same load, the overall height of the truck is raised as a result. Has nothing to do with any increased "stiffness" of the spring.

Leveling by adding spacers or by increasing the "pre-load" accomplishes exactly the same thing -- it just moves the effective position of the lower spring perch on one side of the vehicle in relation to the other.

Edit: Dezertbomber beat me to the punch!

I started going over Hooke's Law in my head trying to figure out what I wasn't getting, and then I remembered about the vehicle weight...

Spend all these years doing the upper level stuff, sometimes you forget the basics. XD

 

[awerking]

Thanks, everyone, for the responses. This board is great!

So the short of it, as I understand it, is "Just set the spring perches so that the truck is level, and don't worry about it, because it doesn't change the spring rate and will feel the same".

Appreciate the clarity!