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Leaf spring theory

Discussion in 'The Garage' started by 84_Chevy_K10, May 11, 2004.

  1. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Anyone have any good sites to the theories reguarding leaf springs? I know we don't talk about this often, but we take for granted all the factors that go into building something that we look at as so, "Simple" as a leaf sprung suspension.

    I feel that with all the factors surrounding this issue, it's about time for a good discussion.

    http://www.rpmnet.com/techart/leaf.shtml

    That one, while interseting, states at the top that it only applies to springs with the shackles above them (compression style)

    Does this mean the whole theory changes when a tension style shackle is used?

    Also, according to that site, by changing my shackle angle to less than 90*, I have effectively stiffened my front springs. This seems completely impossible, but if true, compeltely disproves my theories on why we all should move our front shackle mounts to achieve a better shackle angle.

    Not only that, but if that site is true, we should be moving our shackle brackets back for less angle to soften our rear springs for better off road performance.

    This seems like a complete contradiction, and it's about time for a discussion on this. I don't feel that this belongs in the COG, but I think it's about time we had a complicated discussion about something we dismiss as such a simple piece of equipment we call the leaf spring.

    So, folks, what have you got?
     
  2. az-k5

    az-k5 1/2 ton status

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    That article does mention the reason for a softer ride after a shackle flip and/or longer front shackles. There is a lot more science to a leaf spring set up than a lot of people realize. It is a little too late to go into full "geek" mode and really put some thoughts out.
     
  3. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    That must be a typo or something. Don't make sense at all.
     
  4. BlueBlazer

    BlueBlazer 1/2 ton status

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    [ QUOTE ]
    That article does mention the reason for a softer ride after a shackle flip

    [/ QUOTE ]

    Where /forums/images/graemlins/dunno.gif
     
  5. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I know. It's almost 3 am now, but hopefully when the "geeks" get out of bed and go to work, and get on their computers, we can get into, "full geek" mode.

    I don't have any link plans anytime soon, and neither do a lot of us. If we could start up a tech discussion on leaf springs similar to what we do when we talk about coils and links, we could definitely help a lot of people maximize the performance of the suspension they already have.
     
  6. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    Anyone have any good sites to the theories reguarding leaf springs? I know we don't talk about this often, but we take for granted all the factors that go into building something that we look at as so, "Simple" as a leaf sprung suspension.

    I feel that with all the factors surrounding this issue, it's about time for a good discussion.

    http://www.rpmnet.com/techart/leaf.shtml

    That one, while interseting, states at the top that it only applies to springs with the shackles above them (compression style)

    Does this mean the whole theory changes when a tension style shackle is used?

    Also, according to that site, by changing my shackle angle to less than 90*, I have effectively stiffened my front springs. This seems completely impossible, but if true, compeltely disproves my theories on why we all should move our front shackle mounts to achieve a better shackle angle.

    Not only that, but if that site is true, we should be moving our shackle brackets back for less angle to soften our rear springs for better off road performance.

    This seems like a complete contradiction, and it's about time for a discussion on this. I don't feel that this belongs in the COG, but I think it's about time we had a complicated discussion about something we dismiss as such a simple piece of equipment we call the leaf spring.

    So, folks, what have you got?

    [/ QUOTE ]

    I've got a whole bunch of conversation I had with a guy from Deaver awhile back......... /forums/images/graemlins/peace.gif
     
  7. az-k5

    az-k5 1/2 ton status

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    At the bottom it goes into leaf mounting angles and says that if the front eye is lower than the rear eye the car will be more tight in corners and seem as though the springs are stiffer. It goes on to say that the opposite happens if the front eye is higher than the rear eye. Well a shackle flip lowers the rear eye considerably and creates a lower spring rate. This is why flips can ride better and can get more body roll.
     
  8. BlueBlazer

    BlueBlazer 1/2 ton status

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    I see it now, too bad they do not say how much of a difference can be expected.
     
  9. leadfoot067

    leadfoot067 1/2 ton status

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    well heres what i know....while playing with leaf sprung oval track cars...we made and adjustable upper shackle mount..to change the angle pending track conditions...its a very noticable difference in handling just moving the shackle 1/2 inch either way..so based on that the article has some truth....but it seems to be totally wrong when concerning off road use.....what i know about my blazer leafs.....since i did 52s and 56s and i have shackle angle now....on road it rides so nice,it has a slight bit more lean around corners,and weight transfers alot more on acceleration and braking.....off road it flexes way better....and thats what really matters.
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Compression vs. Tension is completely different. For instance, with a positive arch spring, and the shackle starting at vertical, a compression shackle will effectively lower the spring rate as it compresses, and the shackle angle increases (spring eye moves back). In the same situation with a tension shackle, the spring rate goes to infinity (subject to physical failure and deformation) as the spring compresses. This is why most all full size trucks (expected to haul loads) come with tension shackles.

    And yes, that site description appears to be backwards. This has come up before.
     
  11. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    For instance, with a positive arch spring, and the shackle starting at vertical, a compression shackle will effectively lower the spring rate as it compresses, and the shackle angle increases (spring eye moves back). In the same situation with a tension shackle, the spring rate goes to infinity (subject to physical failure and deformation) as the spring compresses. This is why most all full size trucks (expected to haul loads) come with tension shackles.

    [/ QUOTE ]

    Finally, justification for why I believe shackle flips should not be on towing vehicles.

    As the a compression shackle suspension compresses, effective spring rate decreases.

    With a tension shackle the absolute opposite is true it appears, and as it compresses under load, the effective spring rate increases until physical failure of components makes this impossible.

    Knowing this, I will never have a shackle flip on a tow vehicle. Sadly, lift blocks would be much safer in this instance in my personal opinion.
     

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