TeeLew
Well-Known Member
Let's take a look at the bushing side of things.
On the rear lower forward pickup and the front tension link, these bushings have to accept off-axis motion. This is the 'bind' that is often mentioned. Can we put this into perspective a little? Referenced from static ride, most suspension travel is kept within +/- 5 deg of suspension articulation. Practically all motion is contained within +/- 10 deg of suspension movement. The greater portion of that articulation is taken 'on-axis', with the bushing pivoting relative to the inner crush sleeve. Having said this, there will be a portion of the motion that deflects the bushing. Bushing deflection is not 'bind' any more than coil spring deflection is 'bind'.
When we talk about 'bind' we're talking about things which are meant to deflect, but, for one reason or another, cannot. The type of bushings that we are dealing with are meant to deflect a certain amount. That is not 'bind'; it's purposeful deflection. An obvious example of bind is a spring operating in 'coil-bind', which means it has run out of available travel and the coils are touching. Another example with be a suspension mount which fouls a control arm artificially limiting it's travel.
The SuperPro bushings (I can't speak to the Energy ones), are conical on the ends which contact the suspension mounts. On both the front and rear forward points, The deflection as it goes through normal travel is on the order of a couple mm. We are not talking about some wadded-up, twisted bushing at the limits of its strength. We're talking about a piece of polyurethane deflecting a small amount well within it's elastic limits.
Does the Poly bushing deflect radially when the suspension in loaded in a corner? Of course! It's not meant to have the same installation stiffness as a spherical bearing. Is it less deflection than the stock bonded rubber bushing? Significantly. For one, the rubber bushings take all of their motion elastically, there is no rotation on an inner bonded crush sleeve. Second, the rubber is not only significantly softer than Poly (I agree with the roughly shore 70 estimate of the Superpro material), but, along with the softer material, the stock bushings are often formed with voids that exist to allow different stiffnesses in different deflection modes. Poly bushings provide a significant increase in installation stiffness and a significant decrease in unwanted radial deflection due to cornering loads. I don't have any measurements to quantify the differences in cornering deflection, but it's fair to say that subjectively, the difference is quite large.
Spherical bearings work well in all sorts of applications, but I'm personally hesitant to using them on street cars for a couple reasons. NVH has 3 components. The 'V' is the one that concerns me. Any spherical will necessarily transmit a lot of high-frequency vibrational content into the chassis and there is nothing to soften the impulse loads produced by pot-holes, frost heaves or other all-to-common road imperfections. These are the types of loads which can produce long-term stress fractures and cracking in a chassis. Trying to weld up stress cracks in a chassis is not the most entertaining of tasks (Been there).
Further, sphericals are a service item. 90k miles on a spherical, KellTrac? Congrats, I guess, but I don't run them longer than about 10k when stressed at a higher level. On the street, maybe 20k? Regardless, they do eventually develop lash, corrosion and wear. They are not an item which you can just ignore. The sealing of Ford sphericals is a good step toward a longer life.
In my world, both have appropriate applications. A car which primarily street driven but does some weekend warrior duty will be noticeably improved by installing something like the SuperPro Poly bushings and its manners on the street will be essentially unchanged. A car which is more track-oriented or is used competitively will benefit from the additional installation stiffness of a spherical and its owner will likely have no issue overlooking a relatively minor change in street manners or the additional maintenance.
I've ran my poly bushings for about a year at this point. I have a set of Steeda (w/ extended ball joint studs) front control arms which have sphericals. When they go on, I'll be able to make more of a comparison. I'm not expecting for the difference to be massive, but I'm keeping an open mind. I'll be sure to report back.
On the rear lower forward pickup and the front tension link, these bushings have to accept off-axis motion. This is the 'bind' that is often mentioned. Can we put this into perspective a little? Referenced from static ride, most suspension travel is kept within +/- 5 deg of suspension articulation. Practically all motion is contained within +/- 10 deg of suspension movement. The greater portion of that articulation is taken 'on-axis', with the bushing pivoting relative to the inner crush sleeve. Having said this, there will be a portion of the motion that deflects the bushing. Bushing deflection is not 'bind' any more than coil spring deflection is 'bind'.
When we talk about 'bind' we're talking about things which are meant to deflect, but, for one reason or another, cannot. The type of bushings that we are dealing with are meant to deflect a certain amount. That is not 'bind'; it's purposeful deflection. An obvious example of bind is a spring operating in 'coil-bind', which means it has run out of available travel and the coils are touching. Another example with be a suspension mount which fouls a control arm artificially limiting it's travel.
The SuperPro bushings (I can't speak to the Energy ones), are conical on the ends which contact the suspension mounts. On both the front and rear forward points, The deflection as it goes through normal travel is on the order of a couple mm. We are not talking about some wadded-up, twisted bushing at the limits of its strength. We're talking about a piece of polyurethane deflecting a small amount well within it's elastic limits.
Does the Poly bushing deflect radially when the suspension in loaded in a corner? Of course! It's not meant to have the same installation stiffness as a spherical bearing. Is it less deflection than the stock bonded rubber bushing? Significantly. For one, the rubber bushings take all of their motion elastically, there is no rotation on an inner bonded crush sleeve. Second, the rubber is not only significantly softer than Poly (I agree with the roughly shore 70 estimate of the Superpro material), but, along with the softer material, the stock bushings are often formed with voids that exist to allow different stiffnesses in different deflection modes. Poly bushings provide a significant increase in installation stiffness and a significant decrease in unwanted radial deflection due to cornering loads. I don't have any measurements to quantify the differences in cornering deflection, but it's fair to say that subjectively, the difference is quite large.
Spherical bearings work well in all sorts of applications, but I'm personally hesitant to using them on street cars for a couple reasons. NVH has 3 components. The 'V' is the one that concerns me. Any spherical will necessarily transmit a lot of high-frequency vibrational content into the chassis and there is nothing to soften the impulse loads produced by pot-holes, frost heaves or other all-to-common road imperfections. These are the types of loads which can produce long-term stress fractures and cracking in a chassis. Trying to weld up stress cracks in a chassis is not the most entertaining of tasks (Been there).
Further, sphericals are a service item. 90k miles on a spherical, KellTrac? Congrats, I guess, but I don't run them longer than about 10k when stressed at a higher level. On the street, maybe 20k? Regardless, they do eventually develop lash, corrosion and wear. They are not an item which you can just ignore. The sealing of Ford sphericals is a good step toward a longer life.
In my world, both have appropriate applications. A car which primarily street driven but does some weekend warrior duty will be noticeably improved by installing something like the SuperPro Poly bushings and its manners on the street will be essentially unchanged. A car which is more track-oriented or is used competitively will benefit from the additional installation stiffness of a spherical and its owner will likely have no issue overlooking a relatively minor change in street manners or the additional maintenance.
I've ran my poly bushings for about a year at this point. I have a set of Steeda (w/ extended ball joint studs) front control arms which have sphericals. When they go on, I'll be able to make more of a comparison. I'm not expecting for the difference to be massive, but I'm keeping an open mind. I'll be sure to report back.
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