Coil-Over tuning, springs and valving

[DesertCJ]

I think you guys are getting off track a bit. The springs aren't really there for "absorbing hits". Springs load and then unload and the shock has to control that. The hit absorbing should be done by the shock valving. If you try using springs to absorb hits, you will be in a never ending vicious cycle were you are adding rebound to control the heavy lower spring that's now launching your rig into the air when it rebounds. Now the shock is packing because of all the rebound damping you added to control the heavy lower spring and you might think its bottoming so you add even more spring rate. Rinse and repeat...

 

[mobil1syn]

I think you guys are getting off track a bit. The springs aren't really there for "absorbing hits". Springs load and then unload and the shock has to control that. The hit absorbing should be done by the shock valving. If you try using springs to absorb hits, you will be in a never ending vicious cycle were you are adding rebound to control the heavy lower spring that's now launching your rig into the air when it rebounds. Now the shock is packing because of all the rebound damping you added to control the heavy lower spring and you might think its bottoming so you add even more spring rate. Rinse and repeat...

this guy gets it

 

[Bebop]

I think you guys are getting off track a bit. The springs aren't really there for "absorbing hits". Springs load and then unload and the shock has to control that. The hit absorbing should be done by the shock valving. If you try using springs to absorb hits, you will be in a never ending vicious cycle were you are adding rebound to control the heavy lower spring that's now launching your rig into the air when it rebounds. Now the shock is packing because of all the rebound damping you added to control the heavy lower spring and you might think its bottoming so you add even more spring rate. Rinse and repeat...

That makes total sense.
That still doesn't tell me why I would want a 75% split between my upper/lower rates or why I would want a step up rate of 233% ? What's wrong with no step up rate, a 150% step up rate (like running the heavier one on top, or a 300% step up rate?

I'm just trying to understand spring selection here.

Once again, same example:

125/350 --> 92 lbs/in
150/250 --> 94 lbs/in
175/200 --> 93 lbs/in

Which one do you choose and why ?

 

[DesertCJ]

I'd say that there's nothing wrong with no step up rate. That's why you see the rigs like Campbell's with the single rate setup. Less than 75% and the rebound is uncontrollable while still keeping the characteristics that you want(Fast rebound).

 

[Bebop]

I'd say that there's nothing wrong with no step up rate. That's why you see the rigs like Campbell's with the single rate setup.

Ok, 100% agree.
No step up rate = linear spring rate all the way, you use the shocks to handle the various stages of compression dampening that are needed.

Maybe more suitable with bypasses, which would make sense with the observations made on the Campbell cars and others that run a single rate setup.
Maybe a single coilover could handle this with flutters, but since I have never seen it, I'd wager to say that isn't the case (I might be totally wrong).

Less than 75% and the rebound is uncontrollable while still keeping the characteristics that you want(Fast rebound).

Ok. you're saying that anything less than 75%, we end up with a really high spring load to dampen when at full bump.
This forces us to either put a lot of rebound to control it (which makes the car pack and slows it down) or forces us to live with a car that bucks (quickly shoots up the chassis because of no rebound control over the spring force), correct ?

 

[DesertCJ]

Ok, 100% agree.
No step up rate = linear spring rate all the way, you use the shocks to handle the various stages of compression dampening that are needed.

Maybe more suitable with bypasses, which would make sense with the observations made on the Campbell cars and others that run a single rate setup.
Maybe a single coilover could handle this with flutters, but since I have never seen it, I'd wager to say that isn't the case (I might be totally wrong).



Ok. you're saying that anything less than 75%, we end up with a really high spring load to dampen when at full bump.
This forces us to either put a lot of rebound to control it (which makes the car pack and slows it down) or forces us to live with a car that bucks (quickly shoots up the chassis because of no rebound control over the spring force), correct ?

Yes. I'm not saying 75% though. I don't know where that came from but it seems about right? I'm probably going to try 85% with 150/175 springs on the rear.

 

[Bebop]

Yes. I'm not saying 75% though. I don't know where that came from but it seems about right?

That's what I want to understand.
Where does this 75% come from?

 

[DesertCJ]

That's what I want to understand.
Where does this 75% come from?

Community experience/ Tribal knowledge

 

[Provience]

That's what I want to understand.
Where does this 75% come from?

because you can't get much lower with the spring options that are around. 75% keeps them as close as possible without being the same rate top and bottom. running higher is doable, but the higher you go, the more variation you get for setting up the shock. running a big difference and the stop at or near ride height means you are generally only working with tuning closer to a single rate so you can't use the crossover as an increase in spring rate with sway or big bumps.

 

[Bebop]

because you can't get much lower with the spring options that are around. 75% keeps them as close as possible without being the same rate top and bottom. running higher is doable, but the higher you go, the more variation you get for setting up the shock. running a big difference and the stop at or near ride height means you are generally only working with tuning closer to a single rate so you can't use the crossover as an increase in spring rate with sway or big bumps.

Ok, that makes sense.

In DesertCJ case, with his 150/250 springs, he has too big of a step up rate, which makes the vehicle buck.
Before buying new springs I'd try to flip the current ones around to end up with 250/150 and lower significantly the step up rate without compromising the ride rate. But that definitely doesn't conform to the 75% rule.

 

[mobil1syn]

Ok, that makes sense.

In DesertCJ case, with his 150/250 springs, he has too big of a step up rate, which makes the vehicle buck.
Before buying new springs I'd try to flip the current ones around to end up with 250/150 and lower significantly the step up rate without compromising the ride rate. But that definitely doesn't conform to the 75% rule.

not sure where the 75% came from. 100# spit is my target. you often cant find springs to get your ideal rate so you adjust from here, be it a little more rate, less preload, more preload less spring, etc. DesertCJ rates are good enough with my experience for his rig based on the picture. his combined rates are the same front to rear. i suspect his perfect rates would be 150/250 and 150/200 in the rear. it is not the setup up that is causing the buck, it is the fact that hes got 40s, attached to a 60, pushing against almost no weight above it. he needs more weight if he wants go fast.

 

[Bebop]

it is not the setup up that is causing the buck, it is the fact that hes got 40s, attached to a 60, pushing against almost no weight above it. he needs more weight if he wants go fast.

I have a similar problem and you're not giving me much hope.
But thanks for the honesty.

 

[DesertCJ]

because you can't get much lower with the spring options that are around. 75% keeps them as close as possible without being the same rate top and bottom. running higher is doable, but the higher you go, the more variation you get for setting up the shock. running a big difference and the stop at or near ride height means you are generally only working with tuning closer to a single rate so you can't use the crossover as an increase in spring rate with sway or big bumps.

That's the whole point. You don't want to use a big increase in spring rate to deal with big bumps. Sway, yeah it helps a lot as long as the slide stop is within a couple inches or as much sway as your willing to deal with.

 

[DesertCJ]

not sure where the 75% came from. 100# spit is my target. you often cant find springs to get your ideal rate so you adjust from here, be it a little more rate, less preload, more preload less spring, etc. DesertCJ rates are good enough with my experience for his rig based on the picture. his combined rates are the same front to rear. i suspect his perfect rates would be 150/250 and 150/200 in the rear. it is not the setup up that is causing the buck, it is the fact that hes got 40s, attached to a 60, pushing against almost no weight above it. he needs more weight if he wants go fast.

They're 42s, a 14 bolt and there is actually more sprung weight in the rear than there is in the front. I think your ideal spring estimates are very close. I was going to go 150/175 or even 150/150 though. What you don't know is that the current 150/250 springs have 0 preload because I went into this half blind.

 

[mobil1syn]

I already have the 200x16. I know everyone is used to running the lighter coil high, but I do not see why I cant run the lighter coil low to keep the dual rate closer to the single rate when the crossover stops at 1".

main reason is the lower compresses faster and your take longer to get into the crossover. the slider moves relative to the springs interaction with each other building rate, not the shock travel. also you may run into block height issues. plus you are building rate in a very linear fashion which isnt ideal.

 

[Bebop]

plus you are building rate in a very linear fashion which isnt ideal.

I thought that's what we wanted ?!

 

[HYDRODYNAMIC]

main reason is the lower compresses faster and your take longer to get into the crossover. the slider moves relative to the springs interaction with each other building rate, not the shock travel. also you may run into block height issues. plus you are building rate in a very linear fashion which isnt ideal.

200# x 14" coil binds at 5.5" and I am looking at compressing it to 6" or 7" depending on preload. But when articulating around the bump it would compress to 4 or 5" so I see the cross over would have to go up to allow room. I will have to rework the setup.
I don't see taking longer as a real issue when the crossover is only 1" away and both springs are close in rate.
Why is building rate more linear bad while I see some racers in single rate or have crossovers set to engage so soon its like having a single rate for all up travel and a lower single rate for all down travel?

 

[mobil1syn]

200# x 14" coil binds at 5.5" and I am looking at compressing it to 6" or 7" depending on preload. But when articulating around the bump it would compress to 4 or 5" so I see the cross over would have to go up to allow room. I will have to rework the setup.
I don't see taking longer as a real issue when the crossover is only 1" away and both springs are close in rate.
Why is building rate more linear bad while I see some racers in single rate or have crossovers set to engage so soon its like having a single rate for all up travel and a lower single rate for all down travel?

because they are building rate progressively via motion ratio

 

[HYDRODYNAMIC]

because they are building rate progressively via motion ratio

I assume you are referring to rear trailing arms which I can see the progressive rate, my rear links will be doing this.
For solid axles with near zero progression I am seeing the crossover set very low nearly making them a single rate.

 

[Treefrog]

I assume you are referring to rear trailing arms which I can see the progressive rate, my rear links will be doing this.
For solid axles with near zero progression I am seeing the crossover set very low nearly making them a single rate.

Progressive rate can be acheived without trailing arms. You can also have falling rate, and falling rate in both up and down travel from ride.

 

[Treefrog]

I think you guys are getting off track a bit. The springs aren't really there for "absorbing hits". Springs load and then unload and the shock has to control that. The hit absorbing should be done by the shock valving. If you try using springs to absorb hits, you will be in a never ending vicious cycle were you are adding rebound to control the heavy lower spring that's now launching your rig into the air when it rebounds. Now the shock is packing because of all the rebound damping you added to control the heavy lower spring and you might think its bottoming so you add even more spring rate. Rinse and repeat...

With a change from absorbing hits to storing energy, the plot changes a bit. First the spring force for reference, and then the energy stored. For simplicity I'm tried to use the same numbers as Bebop 's plot. It has 3 inches of preload and is balanced 50% down, 50% up, with 0 being ride.

 

[vetteboy79]

main reason is the lower compresses faster and your take longer to get into the crossover. the slider moves relative to the springs interaction with each other building rate, not the shock travel. also you may run into block height issues. plus you are building rate in a very linear fashion which isnt ideal.

Thank you, I was going to post this. I've had many tuning experiences where someone has 6" uptravel and the crossover at 3" so it comes in "halfway" and they're never actually hitting it.

So regardless of anything else being talked about, everyone keep that in mind: the distance your slider moves and the distance the shaft moves is not 1:1. If you look at that chart and want your crossover to engage after 2" of travel, you don't set it 2" above the slider. With equal springs it would be 1"; adjust accordingly depending on rates.

Like mentioned, the 75% thing is not a 'rule', it's a starting point that generally seems to work OK, developed just through experience. Same as the 1-2" preload to set ride height, values for link separation and length, etc. It gets you close enough that you can narrow changes down to "one thing", which is important in tuning. Starting there generally tells you whether your problem is valving or spring rate. You don't want to change both at the same time.

I'm in the same camp as mobil1syn when it comes to this stuff...I've had the pleasure of doing probably 40-50 shock re-valves on various cars with thewayne, and at a certain point (and he'll tell you the same thing) unless you're super academically curious, sometimes it's ok to just know something works without completely understanding why, and get that shit moving faster to have more fun times in the dirt :)

 

[DesertCJ]

"So regardless of anything else being talked about, everyone keep that in mind: the distance your slider moves and the distance the shaft moves is not 1:1. If you look at that chart and want your crossover to engage after 2" of travel, you don't set it 2" above the slider. With equal springs it would be 1"; adjust accordingly depending on rates."

Lightbulb that little gem affects the spring force curve a lot! I'm going to have to redo the graphs I made to account for that. Lot's of stuff to think about...

 

[vetteboy79]

Lightbulb that little gem affects the spring force curve a lot! I'm going to have to redo the graphs I made to account for that. Lot's of stuff to think about...

It doesn't, really...the force graphs still show what happens when the slider contacts after a certain amount of travel. The physical location of the stop is what changes, and is what you need to keep in mind when tuning stuff.

Put another way, the slider moves 1:1 with the upper spring until it contacts the stop. You can work it back pretty easily knowing the (*change in) force in the spring stack, to where the location of the slider is.

 

[Bebop]

So regardless of anything else being talked about, everyone keep that in mind: the distance your slider moves and the distance the shaft moves is not 1:1. If you look at that chart and want your crossover to engage after 2" of travel, you don't set it 2" above the slider. With equal springs it would be 1"; adjust accordingly depending on rates.

Same lightbulb.
Never even thought about this ! :facepalm:

I'm in the same camp as mobil1syn when it comes to this stuff...I've had the pleasure of doing probably 40-50 shock re-valves on various cars with thewayne, and at a certain point (and he'll tell you the same thing) unless you're super academically curious, sometimes it's ok to just know something works without completely understanding why, and get that shit moving faster to have more fun times in the dirt :)

I still like to know why thought :P

 

[DesertCJ]

It doesn't, really...the force graphs still show what happens when the slider contacts after a certain amount of travel. The physical location of the stop is what changes, and is what you need to keep in mind when tuning stuff.

Put another way, the slider moves 1:1 with the upper spring until it contacts the stop. You can work it back pretty easily knowing the (*change in) force in the spring stack, to where the location of the slider is.

You're right, it doesn't change the graph much. It was only off 1/2" on the travel axis from what I had.

 

[HYDRODYNAMIC]

Adding a drawing to illustrate what I am currently looking at running for the front end. It should be relatable to many builds.
Notes:
14" x 2.5" coilovers with 9 hole piston, 2" x 2.5" air bumps, 4 seater, 60 front, 40"s, links, very common cookie cutter build
1000 lbs per front corner fully loaded with occupants
Non race, but want to go somewhat fast
Bumps are mounted to allow the axle to wrap around the bump for more travel that is why you will see the bump compressed and the coilover still has 2" of travel to flex.
I was originally going to run a single rate, but after seeing many KOH racers using the dual rate I am thinking there must be a good reason. Maybe it just comes down to stability and body roll when going fast.
Notice the difference between running the higher rate on top vs higher rate at bottom.
Also how preload effects ride height, cross over height and coil bind.

 

[HYDRODYNAMIC]

Made a new coil spring swap thread in classifieds.
https://irate4x4.com/classifieds/miscellaneous/328065-i-i-coilover-springs-for-sale-or-trade-i-i

Anyone have anything good or bad to say about Magnitude springs? I know Eibach is the gold standard, but are these worth running?
https://www.magnitudeperformance.com/collections/3-coil-over-springs

 

[DesertCJ]

Never heard of magnitude. I have Blue Coil, they're OK. PAC, again OK but not mind blowing. The last coils I bought were Hypercoil UHT and I really like them. They're barrel springs and even though I haven't seen them bow at all, there's almost no way they can rub on the shock.

 

[AgitatedPancake]

I feel like I recall another recognizable spring MFG name shutting down their offroad coil production, and Magnitude picking up their product line. Or am I misremembering? I can't recall for the life of me, I think it may have been PAC?