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Coil-Over tuning, springs and valving

DesertCJ

Name of Pheel...
Joined
Feb 15, 2021
Member Number
3488
Messages
318
Loc
Central Valley, CA
Seems like this doesn't get talked about much anymore since the old site died a slow death and instagram/Facebook killed tech talk. Yeah, there's the one thread over there that was game changing. It would be cool to get some stuff going over here. If you feel like you have info to share feel free to start an official thread or whatever. I just want to read some tech!

I'll start so this isn't just chitchat. When I got my FOA coil overs, I only had a vague idea about anything. I ordered them with "light" rebound valving and "medium" compression. I hate how they describe that btw. I didn't know what I was doing when I bought springs either so I went the "Old" way with 250lb lowers on the rear and 350lb lowers for the front since the front shocks are leaned back with 5" of shock travel giving 7" of vertical travel at the axle. Right or wrong, my math told me 5/7 is .71 and .71 times 350 is about 250lb. Same as the rear. Of course I bought upper springs that just gave me the ride height I wanted and according to the "NEW" way were all wrong because I also had tripple rate sliders and tender springs on my shocks. My buggy never drove like this.

Right before I finished building, I tore the shocks apart, took off the tripple rate junk, bought longer upper springs and took a stab at revalving all of them based on a couple people I had talked to. So that brings it up to how it sits currently. I'll add that I don't have air bumps or run a sway bar.

Fronts- 125lb over 350lb. Really light rebound and pretty heavy on the compression.

Rears- 150lb over 250lb. Really light rebound and like medium on the compression.

It's good in the rocks, I don't need or want a sway bar. In the whoops it's OK. I don't feel it bottoming ever but I'm not jumping it. Fronts feel good like I somehow blundered into the ballpark on the first go. The rear bucks on the bigger whoops going fast. With a spare tire on the back it cuts the bucking probably in half. I could probably add a touch of rebound and it would be good enough. OR...I could try lighter lower springs on the rear like it was supposed to be with the "NEW" way of tuning. I think the 250lb lowers are launching the rig with the light rebound in the shocks. Lighter lower springs would probably lead to needing more compression valving as well though.

If you have any thoughts on my setup or you feel like sharing yours let's hear it. Just trying to get some discussion going. I read something that alluded to people possibly moving back towards heavier lowers in the racing scene...
 
in and curious to follow along. there was a recent thread it seems like elsewhere talking about tuning. had a bunch of notes in there, i'll need to dig it up and reword a bunch of my notes to bring over here.
 
Fronts- 125lb over 350lb. Really light rebound and pretty heavy on the compression.

Rears- 150lb over 250lb. Really light rebound and like medium on the compression.

It's good in the rocks, I don't need or want a sway bar. In the whoops it's OK. I don't feel it bottoming ever but I'm not jumping it. Fronts feel good like I somehow blundered into the ballpark on the first go. The rear bucks on the bigger whoops going fast. With a spare tire on the back it cuts the bucking probably in half. I could probably add a touch of rebound and it would be good enough. OR...I could try lighter lower springs on the rear like it was supposed to be with the "NEW" way of tuning. I think the 250lb lowers are launching the rig with the light rebound in the shocks. Lighter lower springs would probably lead to needing more compression valving as well though.

If you have any thoughts on my setup or you feel like sharing yours let's hear it. Just trying to get some discussion going. I read something that alluded to people possibly moving back towards heavier lowers in the racing scene...

Do you mind sharing what shim stacks you actually have in your shocks ?

150/250 is a 94 combined rate. You could move to a 175/200 which gives you a 93 rate (basically the same shit) but a lighter lower spring.

PS : I'm interested as I have a similar problem. I need to add a spare but would like to minimize the bucking as much as possible without one.
 
I was actually thinking of just some 175lb lowers with the 150lb uppers for 81lb combined. My shim stacks may or may not help you, rigs are different but I'll share. Rear rebound is 4- .008's, rear compression is 2-.008's, 2-.010's and 2-.015's. Front rebound is 4-.008's, front compression is 2-.008's, 2-.015's and 2-.020's
 
What about keeping the current spring and putting a rebound flutter in the back ?
 
Important specs to list:
Sprung weight per corner
Up travel and down travel per corner from ride height

Then you can set preload 1-2 inches
Upper spring should be around 75% of lower
 
Important specs to list:
Sprung weight per corner
Up travel and down travel per corner from ride height

Then you can set preload 1-2 inches
Upper spring should be around 75% of lower

Yeah. That's straight from the "NEW way" tuning thread. Great info and a good point but I didn't want this to turn into 100 people asking "What springs should I run? Here do my math...":rolleyes:

I know what I can do to improve my setup. If anything, my question is should I just add some rebound valving to the rear and call it good or go all in, swap to lighter lowers and then start over with tuning the rear valving. Probably nobody can really answer that but me? I just wanted to get some discussion going because I like talking and reading about the topic. I'm not 100% sure if going that light on the lower springs(The "NEW" way) would keep a rig from bottoming without air bumps? Add compression until it doesn't bottom? Yeah, now you're harsh in the rough right? Without air bumps there's going to be some compromise I'm sure.
 
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It would need more rebound valving not less...with the current springs.

That would help the bucking, but slow the car down, overall, am I wrong ?

I was thinking flutter but heavier valving in the high speed shims for the current springs. Or the other ones for that matter if you're hitting the same wall after swapping them.
 
Then you can set preload 1-2 inches
Upper spring should be around 75% of lower

So front and rear preload are the same ?
Why should the upper rate be 75% of lowers ?

Not trying to bust your balls, but I have heard these numbers thrown around by multiple people without explanations.
 
20210212_074053.jpg
 
That would help the bucking, but slow the car down, overall, am I wrong ?

I was thinking flutter but heavier valving in the high speed shims for the current springs. Or the other ones for that matter if you're hitting the same wall after swapping them.

I don't know if it would start to pack and slow the rig down overall after adding some rebound. That's where trial and error would have to come in. I think you're right on target though with what I'm thinking.
 
So front and rear preload are the same ?
Why should the upper rate be 75% of lowers ?

Not trying to bust your balls, but I have heard these numbers thrown around by multiple people without explanations.

this is why

Screenshot 2021-02-24 081312.jpg
 
Exactly why I think the 250lb lowers are launching the rear(Bucking). Wouldn't he 100/150 be the blue line on the graph though?
 
I'm assuming blue is 100/100 and there is a typo in the legend.
 
That's less important than the steep rising rate of the lower spring shown. Move that left or right, the result is basically the same.

Not really. The more you move that to the right the less it makes a difference.
 
sprung vs. unsprung weight is the battle the OP is face. keep the spare on all the time
 
OK. Most people would have the step up between 8" and 12" on the graph. You wouldn't want to be riding on the secondary spring at ride height and I'm thinking the higher the slide stop goes, the less effective the secondary spring is going to be? There's definitely some room to play with that though. Personally, I like having it 2-3" above ride height without a sway bar so if it gets some body roll going on it's on the stiffer lower spring to counter it.
 
OK. Most people would have the step up between 8" and 12" on the graph. You wouldn't want to be riding on the secondary spring at ride height and I'm thinking the higher the slide stop goes, the less effective the secondary spring is going to be?

Agreed.

I'm on the opposite side of the spectrum, my slide stop is 1" from full bump / 7" from ride height / 15" from full droop.

There's definitely some room to play with that though. Personally, I like having it 2-3" above ride height without a sway bar so if it gets some body roll going on it's on the stiffer lower spring to counter it.

What I'm saying is there's multiple ways to skin a cat.
That's why I'm trying to understand this 75% rule.
 
If your slider stop is 1" from full bump isn't your upper coil binding before it the slide ever hits the stop? I've read that this 75% rule is to keep it from feeling harsh on the crossover between spring rates. I don't even notice the step up on mine...
 
Not really. The more you move that to the right the less it makes a difference.

the crossover placement is used to modify specific vehicle reactions. so does it make a difference in performance, yes. but can you band aid a large split in the rates by introducing the lower rate later in the travel. what you give up with this is sway control. from springs.
 
If your slider stop is 1" from full bump isn't your upper coil binding before it the slide ever hits the stop? I've read that this 75% rule is to keep it from feeling harsh on the crossover between spring rates. I don't even notice the step up on mine...

Good point. I have long springs and no preload up top.

I've also seen some high end U4 buggies that have the slide stop engaged at ride height with a much bigger discrepancy between upper and lowers than 75%.

That's why I'm trying to understand where does this rule comes from since it's not always used.
 
the crossover placement is used to modify specific vehicle reactions. so does it make a difference in performance, yes. but can you band aid a large split in the rates by introducing the lower rate later in the travel. what you give up with this is sway control. from springs.

Isn't sway control the job of the sway bar though ?
 
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