Spherical bushings

For what? In some places they're appropriate, some not.

performance should be better at the expense of road noise and a harsher ride

I'd be careful on what bushings in the rear suspension you replace with sphericals. The quadra-link suspension is a binding system, and you have to give it the flexibility to move a little bit, or performance will suffer. For the uppers, I would just get a new set of Ford Motorsport HD's.

Unless you're building a 100% drag orientated suspension, do not use solid bushings or poly in the UCA's.

Why no poly in the UCAs? I am getting ready to install a set up HD Double adjustables... primaryily used as a daily driver with a "spirited" style... I am serious about my question. I was thinking them to be more quiet than spherical and more firm than rubber. I have huge tires in the back and have a little rub from side to side movement in my stock UCA's... figured these would help. Panhard bar next step if this doesn't work.

Here's what Maximum Motorsports has to say. I trust their opinion on suspension questions:

For lower control arms:

The bushing configuration of Maximum Motorsports’ rear lower control arms was carefully designed to minimize binding of suspension movement. Most aftermarket control arms use bushing designs which actually cause an increase in suspension bind.
To analyze the geometry involved, Maximum Motorsports used a full scale mock up of the rear suspension. When we tested other aftermarket control arms that had hard urethane bushings at each end, we found they increased the wheel rate by 400%. As little as a 10% change in wheel rate can noticeably affect the handling balance of the car.
So why does the wheel rate increase? In a 4-link suspension design, the control arms do not simply pivot, they also move sideways in an angular motion. If that angular motion is restricted because of a poor bushing design, the suspension will bind up. That binding increases wheel rate which in turn causes unpredictable performance – not to mention damage to the torque boxes. To eliminate this evil situation, MM designed a bushing configuration that allows freedom of suspension movement yet continues to positively locate the axle in the fore and aft directions.

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And for upper control arms:

Maximum Motorsports has found the Ford Racing Performance Parts rear upper control arms to be the best choice for your Mustang. These arms have rubber bushings which allow proper articulation of the Mustang's 4-link rear suspension. Part number M-5500-A comes with bushings at the chassis end which are approximately twice as stiff as the productions bushings.

Click to expand...

Dave

Tom C said:

Why no poly in the UCAs?

Click to expand...

It's too hard. Consider the Mustang 4-link suspension for a moment, specifically the UCA's. They are tasked with the double duty of controlling torsional movement of the axle (in conjunction with the LCA's) as well as controlling lateral deflection. In order to pull off both jobs, compromises must be made. These compromises become glaringly obvious during cornering.

As the suspension articulates in a turn, one UCA moves up and the other moves down. Meanwhile, the LCA's are doing the same. Now if you look at this from above, the axle mounting point of the LCA's remains equadistant from each other (relatively so anyways; with Ford production tolerances being what they are, we can only hope for so much). The UCA's however are a different story.

Since they're canted inward (relative to the axle) to control lateral deflection, the axle mounting points will continuously try to change their distance from each other. Since the axle tends to be fairly rigid, it isn't going to let this happen. Instead, the strain will be taken up by attempting to change the relative length of the UCA's. Again, the steel isn't going to stretch or compress much. The rubber bushings will however.

So as the axle articulates, all the bind created by those UCA's will be absorbed by the soft rubber bushings. If you replace them with poly or steel, the bushings can't deflect and huge amounts of bind is the result.

Now bind by itself isn't necessarily bad. In a sense, your springs are adding bind to the system as they are limiting suspension travel. The difference between good bind and bad bind is predictability.

We all know that our Mustangs have the tendency to understeer. They're nose heavy pigs. Understeer is to be expected. But at the limit of cornering threshhold, our 4-link rear suspensions give us this nasty little demon called "snap-oversteer." Basically, the suspension articulates to the point where huge amounts of bind is introduced into the system. This bind acts as artificial spring rate, effectively incresing the rate of our rear springs by a very noticeable amount. So what was a predictable understeer condition very rapidly (fractions of a second) becomes a oversteer condition. This is "snap-oversteer." I've felt it, both intentionally and unintentionally. It sucks.

Now if the bind increased in a linear rate, it would be fairly predictable. It doesn't though. It's a product of the angle and angle rate of change of the UCA's. It's also 100% dependant on the bushing material.

As I said before, if you're building a suspension where straightline acceleration is the main goal (drag racing), it doesn't really matter. Axle deflection is more of a concern than axle bind at articulation positions you won't see. However, if you are building a dual purpose car, where cornering ability is still desired, skip UCA bushing material that won't allow for compression and distortion. Better yet, get rid of the UCA's altogether, but that's another topic...


On Edit:
Well dang Dave. I guess I could have just copied and pasted from MM too.

baglock1 said:

On Edit:
Well dang Dave. I guess I could have just copied and pasted from MM too.

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I'm lazy, and I don't know 10% of what you do about the Mustang suspension . I just let MM tell me what's best and then I buy it.

Dave

Thanks for the info! I will be rethinking my mods! What about three piece poly in the LCA with a Heim on the other end? I am purchased the Granatelli Wieght Jacker Lowers... but I can still swap out bushings!

Tom C said:

Thanks for the info! I will be rethinking my mods! What about three piece poly in the LCA with a Heim on the other end? I am purchased the Granatelli Wieght Jacker Lowers... but I can still swap out bushings!

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Spherical bearings in the LCA's isn't a problem. I'm running LCA's with heim joints on both ends. It's the UCA's you need to worry about.

But to answer your question, the 3-piece bushing/heim LCA's are a good compromise to keep NVH at a reasonable level. My suspension is all heim joints or delrin (with the exception of the stock UCA's) and it can get pretty noisy sometimes.

Thansk for the info!

from my experiences...

poly's for a street/strip car

sphericals for full strip car

I've had polys for years on the street and can't tell a difference between them and the stock rubber units.

less bind equal better 60ft

Troy