Dialing out a little more oversteer...
09-22-2009, 09:39 AM
#11
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
Sam, I did some reading and, you know, I think you're dead on about the binding.
As I recall, the front end really wanted to lift up under acceleration after installing the part. It came back down again when I moved the front way bar full forward. Is that what you'd expect?
As I recall, the front end really wanted to lift up under acceleration after installing the part. It came back down again when I moved the front way bar full forward. Is that what you'd expect?
I'm starting to think this part is more gear towards drag racing, than handling.
Application: 2005+ Ford Mustang
"The panhard bar bushings on 2005+ Ford Mustangs have a significant impact on your vehicle's ride, comfort, handling, acceleration, noise and vibration. When the vehicle leans (rolls) in a turn, one side of the chassis moves up relative to the rear axle and the other side moves down. The panhard bar must twist to allow for the axle to articulate, this causes the panhard bar bushings to bind. If this bind becomes excessive, it will raise the rear wheel rate and produce sudden and uncontrolled changes in handling such as snap oversteer.
The factory minimizes this suspension bind by using compliant rubber bushings. These soft bushings help accommodate the necessary motion of the panhard bar during body roll. However, the rubber bushings do not provide much in the way of positive lateral support.
It is common to replace the stock rubber panhard bar bushings with polyurethane bushings to resolve the shortcomings of the factory's soft rubber bushings. The downside of polyurethane bushings is they prevent the necessary movement of the panhard bar during body roll, which in turn produces significant binding in the suspension when the vehicle is cornering. The polyurethane bushings also place high stresses on the panhard bar mounts on the vehicle. Polyurethane bushed panhard bars do not allow for rotation of the panhard bar during cornering because of the stiffness of the bushings."
Thoughts?
"The panhard bar bushings on 2005+ Ford Mustangs have a significant impact on your vehicle's ride, comfort, handling, acceleration, noise and vibration. When the vehicle leans (rolls) in a turn, one side of the chassis moves up relative to the rear axle and the other side moves down. The panhard bar must twist to allow for the axle to articulate, this causes the panhard bar bushings to bind. If this bind becomes excessive, it will raise the rear wheel rate and produce sudden and uncontrolled changes in handling such as snap oversteer.
The factory minimizes this suspension bind by using compliant rubber bushings. These soft bushings help accommodate the necessary motion of the panhard bar during body roll. However, the rubber bushings do not provide much in the way of positive lateral support.
It is common to replace the stock rubber panhard bar bushings with polyurethane bushings to resolve the shortcomings of the factory's soft rubber bushings. The downside of polyurethane bushings is they prevent the necessary movement of the panhard bar during body roll, which in turn produces significant binding in the suspension when the vehicle is cornering. The polyurethane bushings also place high stresses on the panhard bar mounts on the vehicle. Polyurethane bushed panhard bars do not allow for rotation of the panhard bar during cornering because of the stiffness of the bushings."
Thoughts?
One thing I don't see involves how much misalignment may be present, as that also goes into determining how much movement needs to be accommodated (or how much roll stiffness is introduced). In addition to the axle and chassis side attachments being offset longitudinally and/or rotationally in side view, it also includes the possibility that the two bolt axes are not truly parallel to each other in plan view. Over time, the poly might cold-flow enough for some of this problem to go away, but I wouldn't want to count on it. Or wait for it.
There is at least one slightly destructive method of removing quite a bit of the "bind" from poly bushings. Yes, do plan on making them periodic inspection/maintenance items afterward and no, don't expect them to live as long.
Norm
Last edited by Norm Peterson; 09-22-2009 at 09:42 AM.
09-22-2009, 11:39 AM
#12
4th Gear Member
Join Date: Dec 2007
Location: Ontario, Canada
Posts: 1,692
Very interesting discussion. So maybe all I needed to do to reduce the "twitchiness" I was feeling last year in the rear end on a road course was to replace the poly/poly PHB and poly/poly LCAs with a poly/rod ones?
I switched to UMI poly/rod LCAs and a FAYS2 Watt's link so everything feels nice and stable now.
I switched to UMI poly/rod LCAs and a FAYS2 Watt's link so everything feels nice and stable now.
09-22-2009, 11:58 AM
#13
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
I'm not surprised.
When I first installed some slightly modified poly bushings in the rear lower arms in this car
and proceeded to drive it over one of my "test loops", I found that they had still added a LOT of rear roll stiffness. Enough to cause noticeably more lateral head-toss. So before tempting fate by driving the car very hard I went back and modified the bushings some more. I can still get the car "loose", but I have to be trying a fair bit harder. With slightly better rear tires (long story) it would be more difficult.
When the LCA bushings AND the PHB bushings are all poly, they work together to create a virtual rear sta-bar. The roll center is still at PHB mid-height, but the PHB now has very little lateral (axial) compliance and the LCAs now offer a degree of lateral resistance. Since these are at different heights, the lateral forces combine to form a couple (aka a moment), in response to body roll. This is separate from (and additive to) the torsional effects of the LCAs by themselves being stiffly bushed.
Norm
When I first installed some slightly modified poly bushings in the rear lower arms in this car
and proceeded to drive it over one of my "test loops", I found that they had still added a LOT of rear roll stiffness. Enough to cause noticeably more lateral head-toss. So before tempting fate by driving the car very hard I went back and modified the bushings some more. I can still get the car "loose", but I have to be trying a fair bit harder. With slightly better rear tires (long story) it would be more difficult.
When the LCA bushings AND the PHB bushings are all poly, they work together to create a virtual rear sta-bar. The roll center is still at PHB mid-height, but the PHB now has very little lateral (axial) compliance and the LCAs now offer a degree of lateral resistance. Since these are at different heights, the lateral forces combine to form a couple (aka a moment), in response to body roll. This is separate from (and additive to) the torsional effects of the LCAs by themselves being stiffly bushed.
Norm
Last edited by Norm Peterson; 09-22-2009 at 12:04 PM.
09-22-2009, 12:14 PM
#14
Former Sponsor
Join Date: Sep 2007
Posts: 1,936
Sam, I did some reading and, you know, I think you're dead on about the binding.
As I recall, the front end really wanted to lift up under acceleration after installing the part. It came back down again when I moved the front way bar full forward. Is that what you'd expect? I'm starting to think this part is more gear towards drag racing, than handling.
I should have read the companies site completely, even the parts I didn't buy. Sophn offers a part just like the one you mentioned Sam, probably because the other one binds. (Not that they tell you that when you order the fixed length panhard bar.)
http://www.spohn.net/shop/2005-2008-...int-Combo.html
Application: 2005+ Ford Mustang
"The panhard bar bushings on 2005+ Ford Mustangs have a significant impact on your vehicle's ride, comfort, handling, acceleration, noise and vibration. When the vehicle leans (rolls) in a turn, one side of the chassis moves up relative to the rear axle and the other side moves down. The panhard bar must twist to allow for the axle to articulate, this causes the panhard bar bushings to bind. If this bind becomes excessive, it will raise the rear wheel rate and produce sudden and uncontrolled changes in handling such as snap oversteer.
The factory minimizes this suspension bind by using compliant rubber bushings. These soft bushings help accommodate the necessary motion of the panhard bar during body roll. However, the rubber bushings do not provide much in the way of positive lateral support.
It is common to replace the stock rubber panhard bar bushings with polyurethane bushings to resolve the shortcomings of the factory's soft rubber bushings. The downside of polyurethane bushings is they prevent the necessary movement of the panhard bar during body roll, which in turn produces significant binding in the suspension when the vehicle is cornering. The polyurethane bushings also place high stresses on the panhard bar mounts on the vehicle. Polyurethane bushed panhard bars do not allow for rotation of the panhard bar during cornering because of the stiffness of the bushings."
Thoughts?
As I recall, the front end really wanted to lift up under acceleration after installing the part. It came back down again when I moved the front way bar full forward. Is that what you'd expect? I'm starting to think this part is more gear towards drag racing, than handling.
I should have read the companies site completely, even the parts I didn't buy. Sophn offers a part just like the one you mentioned Sam, probably because the other one binds. (Not that they tell you that when you order the fixed length panhard bar.)
http://www.spohn.net/shop/2005-2008-...int-Combo.html
Application: 2005+ Ford Mustang
"The panhard bar bushings on 2005+ Ford Mustangs have a significant impact on your vehicle's ride, comfort, handling, acceleration, noise and vibration. When the vehicle leans (rolls) in a turn, one side of the chassis moves up relative to the rear axle and the other side moves down. The panhard bar must twist to allow for the axle to articulate, this causes the panhard bar bushings to bind. If this bind becomes excessive, it will raise the rear wheel rate and produce sudden and uncontrolled changes in handling such as snap oversteer.
The factory minimizes this suspension bind by using compliant rubber bushings. These soft bushings help accommodate the necessary motion of the panhard bar during body roll. However, the rubber bushings do not provide much in the way of positive lateral support.
It is common to replace the stock rubber panhard bar bushings with polyurethane bushings to resolve the shortcomings of the factory's soft rubber bushings. The downside of polyurethane bushings is they prevent the necessary movement of the panhard bar during body roll, which in turn produces significant binding in the suspension when the vehicle is cornering. The polyurethane bushings also place high stresses on the panhard bar mounts on the vehicle. Polyurethane bushed panhard bars do not allow for rotation of the panhard bar during cornering because of the stiffness of the bushings."
Thoughts?
I also sell PHB's like that, such as these:
http://www.stranoparts.com/partdetai...D=79&ModelID=5
http://www.stranoparts.com/partdetai...D=79&ModelID=5
Now that also assumes you want to stay with a PHB's compromised geometry. By design they will jack the body up and down depending on which way you are turning and the balance when pushing hard can and will be somewhat different. I didn't even realize to what extent until I started messing more and more with the Watts link, the entire feel of the back of the car changed.
And Spohn's little write up is neat and all, but it's wrong. It's not binding because the bar is twisting (that's what LCA's do) it's because the PHB when viewed from above on this car isn't straight across the car and there is a twist inherent in a urethane bushing just to install the stupid thing.
If you are interested in swapping bars I'd like to help. I'm around on these forums and I don't let folks make mistakes, at least I try and inform them if I think they might be headed that way--but it's their call in the end. I'm here to supply not just the parts, but the best information I can.
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