polyurothine bushings
12-13-2007, 07:24 PM
#11
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Join Date: Aug 2005
Location: SF Bay.
Posts: 3,035
RE: polyurothine bushings
Any increase or change in your bushings in your UCA will negatively effect your suspension. Do not swap to a urethane uca bushing or aftermarket uca.
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
12-13-2007, 11:27 PM
#13
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Join Date: Aug 2005
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RE: polyurothine bushings
I'm not great at explaining things so I'm gonna copy and paste a bit of what I think most mustang owners should know when they go out buying control arms for the rear...
original poster is known as cgrant on some forums.
-------
Suspension kinamatics is a complex subject at best but I'm going to try to help make it easier to understand.
The following is a simplified 3D model of the Fairmont 4-link used in our Fox and SN95 mustangs. I did this myself and while the scale is not 100% correct, its more than accurate enough to convey the basic ideas I'm trying to explain.
Through the range of axle motion, the UCAs and LCAs must move in a variety of planes to allow axle movement. The first componant is Arc travel. this is the path the end of the UCA makes as it pivots on the chassis pickup point. This is also the path the axle must follow at the UCA and LCA pickup points. Now, the obvious problem here is that you have a rigid axle and 4 seperate links each wit their own arc travel. This means that as the axle moves, the different arcs of the seperate links begin to move in different planes and thus try to fight one another. This is what causes bind.
The next componant is linear compression/expansion This is the tendancy for each link to want to lengthen/compress as it's arc travel begins to oppose the arc travel of the other links.
The last componant is torsional force. At static, the bolts going through the bushings at the chassis and axle are all parallell to each other but as the axle rolls, the angle of the bolts changes right along with it. This means that the link must twist in order to allow the axle to roll.
For the links to be able to contend with these forces, they must have enough compliance to compensate. This is why the stock links have rubber bushings. I'm sure the U-channel design also allows some degree of torsional compliance of the link itself. As the bushings deflect, their resistance to deflection generates bind. The more the deflection, the greater the bind.
When urethane is used, the bushing stiffness increases by 50% which means that they will be less compliant than rubber. The result is that bind happens sooner and is greater. The effect is not linear either, that is to say that when the bushings are 50% stiffer, you don't get just 50% more bind, bind increase is exponential so that 50% increase in stiffness will actually produce more like 150% more bind at the same amount of axle travel. Since the arc length of the LCAs is so much longer than the UCAs and they are closer to parallell to each other, bind is much less of a factor which is why urethane and heim joints work better on LCAs. Since the UCAs are at such harsh angles to one another, they absolutely must have that compliance or severe snap oversteer will result. Now Heim joints remove the torsional aspect of bind but they do not allow for any length compliance so using them in all four links creates obvious problems.
By now it should be obvious that the very nature of a 4 link rear is an inherently flawed design. FOr this reason, any serious handling solution will remove the upper links in favor of something that allows better geometry.
original poster is known as cgrant on some forums.
-------
Suspension kinamatics is a complex subject at best but I'm going to try to help make it easier to understand.
The following is a simplified 3D model of the Fairmont 4-link used in our Fox and SN95 mustangs. I did this myself and while the scale is not 100% correct, its more than accurate enough to convey the basic ideas I'm trying to explain.
Through the range of axle motion, the UCAs and LCAs must move in a variety of planes to allow axle movement. The first componant is Arc travel. this is the path the end of the UCA makes as it pivots on the chassis pickup point. This is also the path the axle must follow at the UCA and LCA pickup points. Now, the obvious problem here is that you have a rigid axle and 4 seperate links each wit their own arc travel. This means that as the axle moves, the different arcs of the seperate links begin to move in different planes and thus try to fight one another. This is what causes bind.
The next componant is linear compression/expansion This is the tendancy for each link to want to lengthen/compress as it's arc travel begins to oppose the arc travel of the other links.
The last componant is torsional force. At static, the bolts going through the bushings at the chassis and axle are all parallell to each other but as the axle rolls, the angle of the bolts changes right along with it. This means that the link must twist in order to allow the axle to roll.
For the links to be able to contend with these forces, they must have enough compliance to compensate. This is why the stock links have rubber bushings. I'm sure the U-channel design also allows some degree of torsional compliance of the link itself. As the bushings deflect, their resistance to deflection generates bind. The more the deflection, the greater the bind.
When urethane is used, the bushing stiffness increases by 50% which means that they will be less compliant than rubber. The result is that bind happens sooner and is greater. The effect is not linear either, that is to say that when the bushings are 50% stiffer, you don't get just 50% more bind, bind increase is exponential so that 50% increase in stiffness will actually produce more like 150% more bind at the same amount of axle travel. Since the arc length of the LCAs is so much longer than the UCAs and they are closer to parallell to each other, bind is much less of a factor which is why urethane and heim joints work better on LCAs. Since the UCAs are at such harsh angles to one another, they absolutely must have that compliance or severe snap oversteer will result. Now Heim joints remove the torsional aspect of bind but they do not allow for any length compliance so using them in all four links creates obvious problems.
By now it should be obvious that the very nature of a 4 link rear is an inherently flawed design. FOr this reason, any serious handling solution will remove the upper links in favor of something that allows better geometry.
12-14-2007, 05:21 AM
#14
6th Gear Member
Join Date: Jan 2004
Location: United States
Posts: 12,575
RE: polyurothine bushings
The entire thing with the UCAs is crap. I have heard this from several different posters, but I could not find any negitive results from doing the LCAs.
The side to side movement of the entire axle package is very small, it had better be or its going to cause serious problems. The article and others like it make it out to seem that the rearend is moving back and forth by several inches... its not.
The people that talk about this are doing so in a situation where you have a BUILT car thats setup for autocross, going 110 perecent thru a corner with a semi professional driver. 99.9999 percent of people will not notice a difference.
I am running the cheap *** blue oval upper and lower c/as in my car, along with a mostly drag racing suspension, and even with the fox 4cyl springs and roush rears, if I turn the struts/shocks up the car handles about 10 times better than stock. I'm sorry, but I just do not buy that you WANT more flex in the rear (rather than less) or that the average person is going to notice the difference of the non rubber bushings in the UCAs causing problems.
The side to side movement of the entire axle package is very small, it had better be or its going to cause serious problems. The article and others like it make it out to seem that the rearend is moving back and forth by several inches... its not.
The people that talk about this are doing so in a situation where you have a BUILT car thats setup for autocross, going 110 perecent thru a corner with a semi professional driver. 99.9999 percent of people will not notice a difference.
I am running the cheap *** blue oval upper and lower c/as in my car, along with a mostly drag racing suspension, and even with the fox 4cyl springs and roush rears, if I turn the struts/shocks up the car handles about 10 times better than stock. I'm sorry, but I just do not buy that you WANT more flex in the rear (rather than less) or that the average person is going to notice the difference of the non rubber bushings in the UCAs causing problems.
12-15-2007, 05:21 PM
#15
5th Gear Member
Join Date: Aug 2005
Location: SF Bay.
Posts: 3,035
RE: polyurothine bushings
ORIGINAL: 2000GT4.6
The entire thing with the UCAs is crap. I have heard this from several different posters, but I could not find any negitive results from doing the LCAs.
The side to side movement of the entire axle package is very small, it had better be or its going to cause serious problems. The article and others like it make it out to seem that the rearend is moving back and forth by several inches... its not.
The people that talk about this are doing so in a situation where you have a BUILT car thats setup for autocross, going 110 perecent thru a corner with a semi professional driver. 99.9999 percent of people will not notice a difference.
I am running the cheap *** blue oval upper and lower c/as in my car, along with a mostly drag racing suspension, and even with the fox 4cyl springs and roush rears, if I turn the struts/shocks up the car handles about 10 times better than stock. I'm sorry, but I just do not buy that you WANT more flex in the rear (rather than less) or that the average person is going to notice the difference of the non rubber bushings in the UCAs causing problems.
The entire thing with the UCAs is crap. I have heard this from several different posters, but I could not find any negitive results from doing the LCAs.
The side to side movement of the entire axle package is very small, it had better be or its going to cause serious problems. The article and others like it make it out to seem that the rearend is moving back and forth by several inches... its not.
The people that talk about this are doing so in a situation where you have a BUILT car thats setup for autocross, going 110 perecent thru a corner with a semi professional driver. 99.9999 percent of people will not notice a difference.
I am running the cheap *** blue oval upper and lower c/as in my car, along with a mostly drag racing suspension, and even with the fox 4cyl springs and roush rears, if I turn the struts/shocks up the car handles about 10 times better than stock. I'm sorry, but I just do not buy that you WANT more flex in the rear (rather than less) or that the average person is going to notice the difference of the non rubber bushings in the UCAs causing problems.
First off, I don't think Green and KT (and certainly not myself) are advocating that more flex in the rear is the goal. What we're saying is that using the stock 4-link configuration forces you to choose between dangerous and unpredictable handling at the limits and a sloppy, loose rear that "tail-wags" like an excited dog. Neither option is very good but the stiffer UCA setup has an increasing bind rate that "spikes" with very little warning.
This can be a difficult concept to explain so I'll give an anecdotal example; imagine driving your car on a cloverleaf on-ramp. You've hit it dozens if not hundreds of times before. Your Mustang has been running springs and shocks/struts for a long time and you can hit 60 mph through it before the wheels start making noise and things feel unstable. It's always bothered you that the rear end wobbles and wags through the turn so you buy a set of brand-X upper control arms with urethane busings. After installing them you hit the cloverleaf again. The car feels much more stable and the rear doesn't wobble like it used to. You get to 60 and everything feels great. The wheels are making a little noise but are planted nicely and much quieter than they were before. You decide to go for 70. You get to 65, the car feels deceptively smooth and before you hear the louder wheel squeal your used to, the rear end suddenly kicks out and you find yourself sideways on a curved on ramp.
So what happened? As your car leaned into the turn, the opposing arcs of the rear links started loading the bushings in tension/compression. The new, stiffer bushings wouldn't give like the rubber ones did so as the axle rolled in relation to the chassis, they added to the wheel rate at an exponential rate. By the time the handling limits were reached, the rate increased so quickly that you didn't have enough warning to ease off the throttle. The problem is that snap-oversteer comes on so quickly and without warning that by the time you realize you have reached the handling limit, there is simply not enough time to smoothly correct. And as you probably know, near or at the limit, any abrupt change to the car's attitude will likely cause it to depart controlled motion. That is the nature of snap oversteer. So, like I said before, your options with the Fairmont Quadrabind are pretty much limited to dealing with the loose rear end or creating a situation where snap oversteer occurs. The only good way to deal with all this is to scrap the stock geometry and switch to a 3 link or parallel link setup.
Now, as far as the average person noticing any problems, I'm sure there are plenty of people that will never push their car hard enough to have snap oversteer, but should anyone with this setup have to swerve to avoid something in the road, they will be at a very high risk of losing control due to snap oversteer. A good analogy for it would be standing under a tree during a thunderstorm. Sure, you don't get as wet but if lightning strikes, your first on the list to get zapped. Its just not worth the risk IMO.
This can be a difficult concept to explain so I'll give an anecdotal example; imagine driving your car on a cloverleaf on-ramp. You've hit it dozens if not hundreds of times before. Your Mustang has been running springs and shocks/struts for a long time and you can hit 60 mph through it before the wheels start making noise and things feel unstable. It's always bothered you that the rear end wobbles and wags through the turn so you buy a set of brand-X upper control arms with urethane busings. After installing them you hit the cloverleaf again. The car feels much more stable and the rear doesn't wobble like it used to. You get to 60 and everything feels great. The wheels are making a little noise but are planted nicely and much quieter than they were before. You decide to go for 70. You get to 65, the car feels deceptively smooth and before you hear the louder wheel squeal your used to, the rear end suddenly kicks out and you find yourself sideways on a curved on ramp.
So what happened? As your car leaned into the turn, the opposing arcs of the rear links started loading the bushings in tension/compression. The new, stiffer bushings wouldn't give like the rubber ones did so as the axle rolled in relation to the chassis, they added to the wheel rate at an exponential rate. By the time the handling limits were reached, the rate increased so quickly that you didn't have enough warning to ease off the throttle. The problem is that snap-oversteer comes on so quickly and without warning that by the time you realize you have reached the handling limit, there is simply not enough time to smoothly correct. And as you probably know, near or at the limit, any abrupt change to the car's attitude will likely cause it to depart controlled motion. That is the nature of snap oversteer. So, like I said before, your options with the Fairmont Quadrabind are pretty much limited to dealing with the loose rear end or creating a situation where snap oversteer occurs. The only good way to deal with all this is to scrap the stock geometry and switch to a 3 link or parallel link setup.
Now, as far as the average person noticing any problems, I'm sure there are plenty of people that will never push their car hard enough to have snap oversteer, but should anyone with this setup have to swerve to avoid something in the road, they will be at a very high risk of losing control due to snap oversteer. A good analogy for it would be standing under a tree during a thunderstorm. Sure, you don't get as wet but if lightning strikes, your first on the list to get zapped. Its just not worth the risk IMO.
12-17-2007, 02:32 PM
#16
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Join Date: Feb 2005
Location: Anaheim, CA
Posts: 616
RE: polyurothine bushings
ORIGINAL: Aereon
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
BTW - when I added the panhard bar, I had to have my Magnaflow exhaust custom re-routed on the passenger side.
[IMG]local://upfiles/12498/93AFFD8212CD47C080E5815A2E5E4C5E.jpg[/IMG]
12-17-2007, 03:35 PM
#17
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Join Date: Aug 2005
Location: SF Bay.
Posts: 3,035
RE: polyurothine bushings
ORIGINAL: jacrockett
The lowest point in my rear is the Tourqe Arm. If you're making enough power to need a TA, then you probably need subframes too. My subframes are welded, and my TA front mount is bolted to the subframes.
BTW - when I added the panhard bar, I had to have my Magnaflow exhaust custom re-routed on the passenger side.
[IMG]local://upfiles/12498/93AFFD8212CD47C080E5815A2E5E4C5E.jpg[/IMG]
ORIGINAL: Aereon
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
Oh, Jacrocket, what is the lowest point in your rear? I have the MM coilovers on the car at about 2 1/4 lower than stock with lower control armsand I'm waiting to install my ta/phb cause of a possible tranny swap. Just wanted to know if I might need to raise the car a bit more when we weld the ta on.
BTW - when I added the panhard bar, I had to have my Magnaflow exhaust custom re-routed on the passenger side.
[IMG]local://upfiles/12498/93AFFD8212CD47C080E5815A2E5E4C5E.jpg[/IMG]
12-17-2007, 06:48 PM
#18
3rd Gear Member
Join Date: Feb 2005
Location: Anaheim, CA
Posts: 616
RE: polyurothine bushings
Good luck. You will love the TA/PHB setup. Mine corners like a *****. According to MM, it's best to wait until you run on the track to see what kind of sway-bar stiffness you need. I ended up staying with the stock sway-bar.
12-17-2007, 11:25 PM
#19
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Join Date: Aug 2005
Location: SF Bay.
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RE: polyurothine bushings
http://www.2kgt.com/item.php?itemid=77 <--- very good article on the rear.
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