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Unread 12-18-2012, 03:57 PM   #31
WKdeuce
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Quote:
Originally Posted by ftgiles View Post
If the separation at the axle is maintained or increased, then the same or smaller upper joints and mounts can be used, but the way the mount interfaces with the axle will have to be stronger. This is the common failure point when extending the upper mounts to just maintain the existing sseparation. Locating the upper arm on the diff side helps in creating a stronger interface.
Thanks. I always (apparently incorrectly) thought it was to hold the mass at it's heaviest point, the way you explained it makes sense though.

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Unread 12-18-2012, 04:25 PM   #32
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I'm also very interested in this topic as I'm doing research for my own build upgrades. I have seen elsewhere it suggested that the link separation at the axle side be a certain percentage of the intended tire diameter in order for them to control the axle effectively. I believe it was close to 25% if I remember right. I'll try and see if I can find the link and post it here. If it's correct a 40" tire should have a link separation of 10" at the axle, but perhaps using bigger joints and stronger mounts and control arms could reduce that amount? If that ratio is accurate then a 35" tire would require 8.75" of separation.
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Unread 12-18-2012, 05:52 PM   #33
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Originally Posted by Necromancer_tat View Post
I'm also very interested in this topic as I'm doing research for my own build upgrades. I have seen elsewhere it suggested that the link separation at the axle side be a certain percentage of the intended tire diameter in order for them to control the axle effectively. I believe it was close to 25% if I remember right. I'll try and see if I can find the link and post it here. If it's correct a 40" tire should have a link separation of 10" at the axle, but perhaps using bigger joints and stronger mounts and control arms could reduce that amount? If that ratio is accurate then a 35" tire would require 8.75" of separation.
You're information is correct. The forces against the control arms are resultant forces that originate from the tire's contact patch.

Draw a straight line vertical from the tire's contact patch through/by the lower control arm pivot point and then through/by the upper arm pivot point. That's the lever that needs to be resolved to understand the forces. And that leverage changes with tire size AND control arm placement.

The force generated at the contact patch is magnified by the lever length between the ground and the lower control arm mount, which is the fulcrum. Then the tire's contact force is magnified in the opposite direction by the length of the lever that exists between the fulcrum and the upper arm's pivot point. The force at the fulcrum is the sum of the force at the contact patch and the force at the upper control arm.

This is a first class lever and follows "lever law" in its theory and calculation. Simple stuff once you define the lever.

If you play with the lever lengths that are affected by moving the control arm mounts and do the force calculations you'll see installing larger tires in combination with moving the control arm mounts further from the ground has a huge impact on the forces seen by the control arms and then transferred into the frame/body. That means a bigger effect on the same anti-squat percentage because that is more force being input, for example. The same anti-squat percentage will behave differently and probably need to be reduced in order to make the vehicle dynamics act in a similar fashion as with smaller tires and lower control arm mounts.
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Unread 12-18-2012, 06:18 PM   #34
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Quote:
Originally Posted by ftgiles View Post
You're information is correct. The forces against the control arms are resultant forces that originate at the tire's contact patch.

Draw a line vertical from the tire's contact patch through the lower control arm pivot point and then through the upper arm pivot point. That's the lever that needs to be resolved to understand the forces. And that leverage changes with tire size.

The force generated at the contact patch is magnified by the lever length between the ground and the lower control arm mount, which is the fulcrum. Then the tire's contact force is magnified in the opposite direction by the length of the lever that exists between the fulcrum and the upper arm's pivot point. The force at the fulcrum is the sum of the force at the contact patch and the force at the upper control arm.

This is a first class lever and follows "lever law" in its theory and calculation. Simple stuff once you define the lever.

If you play with the lever lengths that are affected by moving the control arm mounts and do the force calculations you'll see installing larger tires in combination with moving the control arm mounts further from the ground has a huge impact on the forces seen by the control arms and then transferred into the frame/body. That means a bigger effect on the same anti-squat percentage because that is more force being input, for example. The same anti-squat percentage will behave differently and probably need to be reduced in order to make the vehicle dynamics act in a similar fashion as with smaller tires and lower control arm mounts.
Thanks for breaking that down a bit for me, it helps to be able to visualize it in my head better! I'm assuming that since the bushing material would be the same when using the same size links, that a larger separation distance will allow said bushings better control over the axle, and using the same logic in reverse I would assume once again that reducing the link separation on the axle side would require larger arms/joints/bushings (Read: Stronger) to retain the same control that larger link separation achieves.
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Unread 12-18-2012, 07:01 PM   #35
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Originally Posted by Necromancer_tat View Post
Thanks for breaking that down a bit for me, it helps to be able to visualize it in my head better! I'm assuming that since the bushing material would be the same when using the same size links, that a larger separation distance will allow said bushings better control over the axle, and using the same logic in reverse I would assume once again that reducing the link separation on the axle side would require larger arms/joints/bushings (Read: Stronger) to retain the same control that larger link separation achieves.
You've got it. Here's a quick picture to plug some numbers into. Put stock tire and control arm distances in and then compare your proposed. Very revealing.


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Unread 12-19-2012, 04:27 PM   #36
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Quote:
Originally Posted by ftgiles View Post
You've got it. Here's a quick picture to plug some numbers into. Put stock tire and control arm distances in and then compare your proposed. Very revealing.


Thanks for the diagram and equation! After looking at it and thinking a bit, I now have several other questions and ideas. I'm gonna do a little Googling and see what I can figure out, but I might do some drawings in MS Paint and make another thread instead of steering this one off course.
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