Coil over spring rates

candocantrell · Apr 23, 2018

Ive got some questions about the equivalent spring rate that i need for my jeep.

ive got a full body YJ with 5.3, th400, atlas, .120 cage, dana 60 front, 14 bolt rear, and 42's with H1 beadlocks (just for weight reference)

Ive got 14" radflo's on all 4 corners
I bought 200 lb/in springs for the front and 150 lb/in and used the deflection of the springs to calculate the sprung weight of the jeep.

deflection was 4" on all 4 corners with above spring rates, so that tells me that my front sprung weight is 800 lb per corner and my rear sprung weight is 600 lb per corner.

I'm shooting for 6" of up travel and 8" of droop.

With these numbers i called WOD and Adam told me that the equivalent spring rate should be the weight at any given corner divided by the length of droop that i am going to have.

That gives me equivalent spring rate up front of 800 lb / 8 in = 100 lb/in.... with the 200 lb spring rate that i have now, to get 100 lb equivalent i need to stack another 200 lb spring on top. so 200 over 200

The math is the same for the back 600 ln / 8 in = 75 lb/in for the equivalent spring rate.. with the 150's i have now i will need to stack 150 over 150 to get the equivalent 75 lb/in spring rate.

Spring rate is a subjective number so i know there may not be a right or wrong answer but im wanting some opinions based on the numbers i have. The people ive talked to so far say that these spring rates seem VERY stiff for the application.

Let me know what you think..

Thanks In Advance.....

rugger99 · Apr 23, 2018

Get in contact with Ryan at AccuTune. He is on this board under TRD. He is very knowledgeable regarding coilovers, springs,setup, etc..

TacomaJD · Apr 23, 2018

Is that calculated in with using a lower spring that is 2" longer than shock travel and upper spring equal to length of shock travel? If so, probably not entirely off by too much. My old full body yota with 4 banger and lots of exo cage with 14" fox 2.0 coilovers ON THE FRONT (air shocks rear) had 14" 150 lb upper spring and 16" 200 lb lower spring and rode plenty soft enough. Started out with 100 over 200 in the same lengths and it was way too soft, had preload cranked way down to get ride height I needed and was stupid soft. Swapping in a 150 lb top spring made a good difference in that I did not have to crank preload that much to achieve ride height, therefore allowing plenty room to let the top spring absorb all the minor bumps in the trail before the lower spring would have to kick in and work, if that makes sense.

I'm no shock expert, but I don't think those numbers are too far off at all for a good starting point. And a lot of times, if you order springs from someone like WOD or EOR, they'll let you do a spring exchange if you need to change up your spring rate one more time to fine tune it. That's what I did, ordered mine from EOR. Check with Adam or whoever you order from first to see if this is an option.

Edit: Only thing I've not fully grasped in its entirety that sticks out to me is the 200/200 being the same rate spring on top and bottom. The cool thing about dual rate coilovers is adjusting your dual rate stop ring so that after a certain amount of up travel, the stop ring kicks in on the lower spring to greatly increase dampening or whatever term you want to use for getting stiffer. So the idea is to have your dual rate stop ring set so that if you are hauling ass down a mildly bumpy trail you are riding on the softer top spring, but when the uptravel begins to get worse when going over bigger stuff, the dual rate stop ring makes the lower spring kick in and further helps to stabilize the rig until it droops back out. hence why I would think it would be ideal to have a lighter top spring than lower spring, like 175/225 or something like that. But like I said, I'm just an amateur....so don't take anything I say to the bank. Lol

candocantrell · Apr 24, 2018

Edit: Only thing I've not fully grasped in its entirety that sticks out to me is the 200/200 being the same rate spring on top and bottom. The cool thing about dual rate coilovers is adjusting your dual rate stop ring so that after a certain amount of up travel, the stop ring kicks in on the lower spring to greatly increase dampening or whatever term you want to use for getting stiffer. So the idea is to have your dual rate stop ring set so that if you are hauling ass down a mildly bumpy trail you are riding on the softer top spring, but when the uptravel begins to get worse when going over bigger stuff, the dual rate stop ring makes the lower spring kick in and further helps to stabilize the rig until it droops back out. hence why I would think it would be ideal to have a lighter top spring than lower spring, like 175/225 or something like that. But like I said, I'm just an amateur....so don't take anything I say to the bank. Lol
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That's the thing about stacking springs in series... although both springs have same spring rate individually, their equivalent spring rate is calculated like this, with K representing spring rate, 1/K_eq=(1/K_1)+(1/K_2).

It is counter intuitive but that is how the math works.

My question is more about whether or not the 100 lb/in equivalent rate is a good number to shoot for based on my weight and shock travel numbers.

I appreciate the reply!!!

BustedKnucklefilms · Apr 24, 2018

This video might help- https://www.youtube.com/watch?v=4FZp_oDGQNY

Burkey knows his stuff, and is a dealer for PAC and a few other spring companies.
Give him a shout and he can get you setup with the right springs- www.bustedknuckleoffroad.com

RustyC · Apr 24, 2018

200 over 200 is a combined rate of 100. When the dual rate slider hits the stop the rate will jump to 200 using only the lower spring. That is the step up rate. Very useful for sway or roll control.

TRD · Apr 24, 2018

rugger99 said:
Get in contact with Ryan at AccuTune. He is on this board under TRD. He is very knowledgeable regarding coilovers, springs,setup, etc..

Thank you!

We're happy to help and we can calculate your rates using our equations. We have the easiest and cheapest springs swapping policy. And we have a HUGE inventory so springs ship quickly.

TacomaJD · Apr 24, 2018

Re: Re: Coil over spring rates

RustyC said:
200 over 200 is a combined rate of 100. When the dual rate slider hits the stop the rate will jump to 200 using only the lower spring. That is the step up rate. Very useful for sway or roll control.

Ah-ha, that makes sense now.

Sent from my SM-G930V using Tapatalk

rpf500 · Apr 24, 2018

rugger99 said:
Get in contact with Ryan at AccuTune. He is on this board under TRD. He is very knowledgeable regarding coilovers, springs,setup, etc..

I agree. If you have not already, contact Accutune. I also agree the rates you mentioned seem high.
I have a similar set up as you do. At one point I had 150/200, changed rates about 3 different times, then I finally got in touch with someone (RYAN) who helped so I could quit guessing.

Here is where I am at currently. You might not end up with these same rates, but you'll be close if I were to bet.

125/150 front with 6" shaft at ride height
100/125 rear with 7" shaft at ride height

Bebop · Apr 26, 2018

candocantrell said:
With these numbers i called WOD and Adam told me that the equivalent spring rate should be the weight at any given corner divided by the length of droop that i am going to have.

Wouldn't (or shouldn't) preload and N2 pressure affect this calculation ?