Preloading LR

[Dirtmod13]

I tried running a softer left rear spring and noticed that I needed a lot of preload to get bite/ ride height. Chassis builder says not to tighten past the point where adjuster nut just touches spring at full droop. When going from 200 to 175 I had to go way past that point. So why does rocket say not to let adjuster go past touching the spring?The way I see it is the Spring pressure would push the birdcage down at an accelerated rate vs not touching the spring to the nut. Any thing I'm missing? I assume the stacks would have to be preloaded also.

[Rayburnt1]

Yes it ends up preloaded with a stack. Call them and get the newest stuff.

[A ron]

Dumb question? Does the softer left rear add forward drive from the center off since it stays on the spring?

[Lizardracing]

the way I see it...and a much over simplification,

The effect has much to do with the indexing of the BC. Why?
At RH, the spring is holding up the car and has much effect on tire loading.
The weight the spring is carrying and loading the tire diminishes with the amount of hike as more weight moves from the spring to the bars.
At full hike, the weight of the car is mostly on the bars and the spring has little effect.

Depending on where you have the bars, the lenght, the travel etc. and how much the BC indexes, the amount of load from the spring during raise and fall of the car on/off the bars changes. The more BC indexing, the more the spring is trying to push the BC down and the axle up(opposite and equal reaction) so the how fast the weight moves from the spring to the bars is key.

If the driver can hold up the car on the bars the whole way around, the wheel load doesn't really change too much with spring changes unless the spring is heavy enough to push down on the BC hard enough to lift the tire and that would tighten everywhere because the chassis couldn't come up on the bars. That would also be excessive and likely outside the range of a typical car design. No one uses a 1000lb LR spring after all.

So don't look at it as the amount of preload as the adjustment but instead how much that spring is pushing down on the BC and lifting the tire at the various points of raise and fall of the car. Typically, more spring reduces the weight progression between RH and full hike loosening the car while the car is climbing the bars.

On my car I use a 150lb spring on the LR and the BC indexes only 1/4" so the effect is pretty small to none. But if some night I grabbed a 1500lb spring by mistake, a 1/4 inch BC index means a slower transfer of weight between RH and full hike but at full hike when the car is on the bars.

[Dirt_Buster]

In my opinion it's more consistent as well as easier to drive which in result makes it more consistent. Haha. I like the 100-125

[Matt49]

At full travel, whether the spring is loaded or not really doesn't matter. As lizard said, the bars are providing the lift because of anti-squat and the spring isn't much of a player at that point.
To me, the softer spring provides faster transition to the bars getting increased angle. I'll try to explain:
Imagine an axle with a 200 pound LR and a 200 pound RR spring. Let's assume they are both loaded 4 inches (800 pounds on each spring) at static ride height. Then let's assume that we get a lateral weight transfer (from left to right) of 400 pounds (imagine entering a corner). In this case the RR spring is going to compress another 2 inches and the left rear spring is going to rebound 2 inches. Now imagine the same axle, same car, same ride heights but with a 100 pound LR and 200 pound RR. And also assume that the springs both have 800 pounds on them. Now the RR is still loaded 4 inches but the LR is loaded 8 inches. And when we re-run our test and pretend to transfer 400 pounds laterally, the RR spring still compresses 2 inches but the LR spring rebounds 4 inches.
So you have increased travel for the same amount of weight transfer which is quickening how fast the car "bars up" on the left side before you even apply any throttle to help it.
This is why a softer LR spring usually makes the car tighter on initial throttle. Because you have more left side bar angle to start with.
This is of course contrary to the old "heavy spring gets the weight" school of thought which would tell us that a stiffer LR spring would tighten entry due to increased dynamic wedge. There's just a lot more going on with these cars to only consider the load that spring puts on a tire. There are other dynamics at work.

[A ron]

Thanks All. Sorry for hijacking the thread. Info in that area was just contradicting from post to post and sheet to sheet, but Matt that makes sense.

[lindsey97]

"This is of course contrary to the old "heavy spring gets the weight" school of thought which would tell us that a stiffer LR spring would tighten entry due to increased dynamic wedge. There's just a lot more going on with these cars to only consider the load that spring puts on a tire. There are other dynamics at work. "

I'm glad someone is finally publicly discarding this theory. I believe this has confused so many people.

[MasterSbilt_Racer]

"This is of course contrary to the old "heavy spring gets the weight" school of thought which would tell us that a stiffer LR spring would tighten entry due to increased dynamic wedge. There's just a lot more going on with these cars to only consider the load that spring puts on a tire. There are other dynamics at work. "

I'm glad someone is finally publicly discarding this theory. I believe this has confused so many people.

There have been a lot of discussions about that on here in the past. If you have a symptom/correction cheat sheet from the early 2000s, you are so screwed on a lot of things. You have to have some grasp of vehicle dynamics.

[Lizardracing]

That theory has merit on three links, triangulated four links, truck arms, and leaf springs among others less used.
The BC changes the simple lever machine and and adds another lever to the system.

[Crash101]

Just took the car off scales. Got all the ride heights and numbers we wanted. However when the rear end is hanging at full droop the nut is 4 turns off the spring on LR. Will that be ok?

[7uptruckracer]

Yeah, just depends on you, spring, most drivers trailbrake so it shouldn't be really free falling.

[let-r-eat]

The laws of physics won't be debunked anytime soon. Peoples understanding of those laws will.

[Dirt_Buster]

Keep pressure on the spring. Drop a weight from a few inches from your hand and see how much it upsets your hand. Unless you're crutching the car with a LR shock I'd say keep some pressure on it. Unless you're also a master of both feet doing work brake and gas at the same time which takes a lot of practice and feel then keep spring loaded. It's easier to drive in traffic as well.

[RCJ]

The phrase should be "all things equal the stiffest spring gets the weight" or "the stiffest corner of the car gets the weight".I've seen data that would suggest that with a 200 l/r and a 225 r/r, because of motion ratios the l/r is a lot stiffer.