Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1956198
11/23/15 12:02 AM
11/23/15 12:02 AM
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Joined: Jun 2003
Posts: 9,225 Charleston
sixpackgut
Drag Week Mod Champion
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Drag Week Mod Champion
Joined: Jun 2003
Posts: 9,225
Charleston
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I more complicated than that. It depends on angles and attaching points
Gen 3 power 6.22@110, 9.85@135 Follow @g3hemiswap on instagram
performance only racing, CRT, ultimate converter, superior design concepts, ThumperCarbs
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1956233
11/23/15 01:00 AM
11/23/15 01:00 AM
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Joined: Mar 2006
Posts: 9,835 MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,835
MI, usa
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It does matter but not as much as you think. If the shocks are behind the axle the rears will need to be either 110### or 130. Track use only 110#, street may require 130# for compression control to keep from bottoming out. Mine weighs 1520# on the rear. I measured the unsprung weight. Dana, old school American 200S, M/T 10.5wx31, Will-wood. Then 1/2 of the Koni aluminum coil overs and ladder bars. That weight was 330#. My springs are compressed 3.5" at ride height with driver. So 130x3.5"=455#/side. 455x2=910. 1520-330 (unsprung)=1190. That being said I'm surprised there is a 280# (1190/910) difference with the shocks only 4" behind the axle. Obviously the calculation doesn't match reality
Doug
Last edited by dvw; 11/23/15 03:00 PM.
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1956282
11/23/15 02:27 AM
11/23/15 02:27 AM
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Joined: Jun 2003
Posts: 9,225 Charleston
sixpackgut
Drag Week Mod Champion
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Drag Week Mod Champion
Joined: Jun 2003
Posts: 9,225
Charleston
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Can you get about 2" compression on your spring sitting? I have 350 in mine at around 1750 on the nose
Gen 3 power 6.22@110, 9.85@135 Follow @g3hemiswap on instagram
performance only racing, CRT, ultimate converter, superior design concepts, ThumperCarbs
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1956300
11/23/15 02:49 AM
11/23/15 02:49 AM
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Joined: Dec 2005
Posts: 11,552 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,552
Fulton County, PA
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Without knowing what shocks, suspension, shock location and installed length at ride height, street, strip or both, ET, spring free length, spring compressed length at ride height now etc. anything would be a guess. Race only, shocks behind the housing, ladder bars, typical backhalf deal? Probably a step too tight on both ends.
If the results don't match the theory, change the theory.
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Re: Coil spring rate discussion
[Re: sgcuda]
#1957982
11/25/15 11:41 PM
11/25/15 11:41 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Slightly off topic, but not really. Is there an easy way to determine what springs I already have in my car? Most any spring will have a tag or the number etched on the flat of the spring on the end with the pounds per inch... if you dont want to do the formula.. set the bottom spring adjuster to 1" up from the bottom... is the shock at the design length with the car at race weight... if you have to move the adjuster more than 1" then you need a different springs... if its a A-body then a 130 will be close but might need a change one way or another
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1957993
11/25/15 11:55 PM
11/25/15 11:55 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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the spring rate is whatever is needed to just hold the car up
2 things are missing:
1. there's more than one way to get the car to the same ride height (assuming you know what you want already): A. short stiff spring - stops transferring weight when it tops out B. long weak spring, the extra length is pre-load - transfers weight up to its full length
2. spring stiffness must be enough to control the weight of the unsprung components (axle etc.). An 8-1/4" and a Dana need different rear springs regardless of the rest of the tuneup.
Boffin Emeritus
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Re: Coil spring rate discussion
[Re: polyspheric]
#1958003
11/26/15 12:07 AM
11/26/15 12:07 AM
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Joined: Jan 2005
Posts: 4,243 Charlotte, North Carolina
sgcuda
master
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master
Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
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the spring rate is whatever is needed to just hold the car up
2 things are missing:
1. there's more than one way to get the car to the same ride height (assuming you know what you want already): A. short stiff spring - stops transferring weight when it tops out B. long weak spring, the extra length is pre-load - transfers weight up to its full length
2. spring stiffness must be enough to control the weight of the unsprung components (axle etc.). An 8-1/4" and a Dana need different rear springs regardless of the rest of the tuneup. Not really. In my case, the coil overs are a given length. So because there is less energy loss per inch in the weaker spring , it would top out quicker with the weak spring than the stiff one. I have never heard of controlling the unsprung components. How would you know when your spring values are too low to handle the unsprung weight. We all know what would happen if you had too low a spring pressure for the sprung weight. And when I lightened my car, I had to change springs several times to get it down from it's 4x4 stance.
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Re: Coil spring rate discussion
[Re: polyspheric]
#1958039
11/26/15 01:17 AM
11/26/15 01:17 AM
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Joined: Mar 2006
Posts: 9,835 MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,835
MI, usa
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the spring rate is whatever is needed to just hold the car up
2 things are missing:
1. there's more than one way to get the car to the same ride height (assuming you know what you want already): A. short stiff spring - stops transferring weight when it tops out B. long weak spring, the extra length is pre-load - transfers weight up to its full length
2. spring stiffness must be enough to control the weight of the unsprung components (axle etc.). An 8-1/4" and a Dana need different rear springs regardless of the rest of the tuneup. I agree with comment #1 Comment #2 is dead wrong. The spring doesn't control the housing. That would be the job of the shock. Doug
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1958398
11/26/15 03:48 PM
11/26/15 03:48 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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Comment #2 is dead wrong
LOL
I think you mean "I don't understand what you said".
Boffin Emeritus
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Re: Coil spring rate discussion
[Re: TheOtherDodge]
#1958399
11/26/15 03:50 PM
11/26/15 03:50 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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Let's save time in future.
I won't correct the mistakes, and you can just say "You're wrong" anyway.
Boffin Emeritus
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Re: Coil spring rate discussion
[Re: polyspheric]
#1958418
11/26/15 04:40 PM
11/26/15 04:40 PM
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Joined: Dec 2005
Posts: 11,552 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,552
Fulton County, PA
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the spring rate is whatever is needed to just hold the car up
2 things are missing:
1. there's more than one way to get the car to the same ride height (assuming you know what you want already): A. short stiff spring - stops transferring weight when it tops out B. long weak spring, the extra length is pre-load - transfers weight up to its full length
2. spring stiffness must be enough to control the weight of the unsprung components (axle etc.). An 8-1/4" and a Dana need different rear springs regardless of the rest of the tuneup. The spring has to be the correct rate to hold the car up at the desired ride height when compressed to the desired length. The spring rate and the resulting compressed length is a tuning decision. Having the spring in coil bind before the shock is fully compressed OR having a spring that holds the car up with zero spring compression are the only wrong choices. The choices between those 2 extremes are determined by how you want or need the spring to influence suspension movement. If a spring "tops out" or reaches free length at any time during a run, something is wrong. A lighter spring has to be compressed more which stores more energy than a heavy spring which is only slightly compressed. This energy can be used to help get the housing out in a car that needs help getting the tire applied at the hit. Higher horsepower applications don't need that influence and will use a heavier spring with less energy stored at ride height. Think about the 6 cylinder torsion bars helping get the front end separated on cars that need the pitch rotation. Same effect. While the weight of the unsprung components may influence a spring choice (total weight-unsprung weight=sprung weight), the spring doesn't control what the axle does. It influences it, but the shock is what controls it. Suspension type and geometry, spring rates and shock adjustments all work together to determine what happens as the car moves down the track.
If the results don't match the theory, change the theory.
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