RLCA Help: Spherical Bearing vs. Poly Bushing

[buttsy]

I have installed the following superpro bushes
Rear lower control arm
inner and outer camber
front castor

I also completed a number of other upgrades at the same time. So I cannot compare or comment on the differences between bearing or bushes. Prob the main reason for going with poly was the percieved longevity of the poly bushes. I was worried that the bearing may wear over time which would cause excessive play therefore noise. And then I would have to go through the process again. From my research, the poly should outlast the bearing. And still provide a far greater level of feedback and control than the standard rubber bushes. Perfect, I believe for my intended purpose. Which is spirited road use and 3 track days a year. No track use as of yet though. Harrop oil cooler needed.
I have no complaints as to how the car currently rides. Firm and controlled. But never Harsh. Road noise on coarse chip has actually been reduced from when I had only the BMR cradle lockout installed to an otherwise stock vehicle. Which I found interesting. Due to the ford track pack struts high speed compression valving and the superpro bushes I believe.

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[Brian@BMVK]

The GT4 version of the car has been relatively successful in racing. The Camaro hasn't had much team consistency, but they're always very quick.

I bet the difference isn't that big from behind the wheel. At least it's not on the watch.

Well yeah, they fix it for the GT4. Solid subframe bushings, sphericals at all major control points. I wish I took a picture when I was in the Kohr garage.

 

[NGOT8R]

Only time will tell how well either setup holds up. I expect my Steeda RLCA bearing to last a very long time, as I don’t put a lot of miles on my car since it’s not my daily. The real test for me will be the times when I am able to take it to the drag strip, followed by more street driving and a thorough post inspection. as someone said in a a different thread; there aren’t many people who have done or would be willing to do this mod again. For me, it cost me a damaged 12 ton shop press, after which I had to enlist the help of my buddy to get the old bushings out and the new bearings in. Overall, I though it was a PITA of an install, but I’m hoping the end results help me to forget about what I went through to do this mod. Having said all of that, just looking at the bearing and even photos of the SuperPro bushings, they both look far superior to the stock bushing.

I say to anyone thinking of this mod; “Do it!” worst case scenario is, if you don’t like it, a swap back to a set of stock control arms will only be half the trouble of installing a new bushing/bearing.

 

[Norm Peterson]

@TeeLew @Norm Peterson hopefully you both know that I respect your knowledge and thoughts very much. There are certainly merits to consider, though I'm not sure that they outweigh the handling, ride and grip benefits observed by reducing or removing the (very significant relative to the spring and bar rates) multi-axial rate and geometric deflection from the OEM design.

I think we're looking at opposite sides of the same coin here. When you lose wheel rate directly through reduced on-axis bushing stiffness and make things either bind more with poly or make them bind less with sphericals for the off-axis stuff, there will be wheel rate and TLLTD consequences. At that point it's up to the individual to decide how he wants to re-balance the car - which is something he might want to do anyway even if the suspension bushings were left untouched. I'm not forgetting about the downstream effects of bushing stiffnesses here. It's just downstream of distinguishing between geometric bind and rotational joint stiffnesses as being the source.

The on-axis stiffness is really just another suspension spring acting in parallel with the obvious ones. That's not the problem. It's the off-axis effects that I don't see as being desirable, that they're simply the unavoidable consequences of bushing material and design that have to be worked around and used as inputs elsewhere in the design process.

If I'm looking for a rear roll resistance of, say, 10,000 in*lbs/°, I'm really going to prefer that I get it from X amount of roll resistance in the springs (plus any on-axis bushing effect) and (10000 - X) from the rear bar with negligible off-axis bushing effects. If I throw away the OE on-axis bushing stiffness, yeah, I'm going to need a bit more spring or possibly a bit more bar than if I didn't. If I add much off-axis stiffness, a little less bar. But that shakes out in the test driving, usually meaning a bar stiffness adjustment from where I initially thought it might end up.

Basically, as a one-man operation I don't have access to what Ford does when it comes to bushing design, so my options there are limited to what is readily available and what I might do to that as further modification. On the other hand, I have some freedom to choose suspension configurations that might not meet things like corporate standards on NVH and ride quality.


Norm

 

[Brian@BMVK]

I think we're looking at opposite sides of the same coin here. When you lose wheel rate directly through reduced on-axis bushing stiffness and make things either bind more with poly or make them bind less with sphericals for the off-axis stuff, there will be wheel rate and TLLTD consequences. At that point it's up to the individual to decide how he wants to re-balance the car - which is something he might want to do anyway even if the suspension bushings were left untouched. I'm not forgetting about the downstream effects of bushing stiffnesses here. It's just downstream of distinguishing between geometric bind and rotational joint stiffnesses as being the source.

The on-axis stiffness is really just another suspension spring acting in parallel with the obvious ones. That's not the problem. It's the off-axis effects that I don't see as being desirable, that they're simply the unavoidable consequences of bushing material and design that have to be worked around and used as inputs elsewhere in the design process.

If I'm looking for a rear roll resistance of, say, 10,000 in*lbs/°, I'm really going to prefer that I get it from X amount of roll resistance in the springs (plus any on-axis bushing effect) and (10000 - X) from the rear bar with negligible off-axis bushing effects. If I throw away the OE on-axis bushing stiffness, yeah, I'm going to need a bit more spring or possibly a bit more bar than if I didn't. If I add much off-axis stiffness, a little less bar. But that shakes out in the test driving, usually meaning a bar stiffness adjustment from where I initially thought it might end up.

Basically, as a one-man operation I don't have access to what Ford does when it comes to bushing design, so my options there are limited to what is readily available and what I might do to that as further modification. On the other hand, I have some freedom to choose suspension configurations that might not meet things like corporate standards on NVH and ride quality.


Norm

Nothing stated incorrect.

The only issue I see with the on-axis stiffness (and the off-axis that can never be eliminated) is that when you think outside of just roll resistance, it's quite compromised. That stiffness acts not only in roll but in jounce. It also acts like a bar on the inside tire in roll, resisting the main spring that's trying to push the tire back into the road. All the downside of a bar, none of the upside (ride compliance). All downside of a spring, without the upside (ride rate & roll rate but doesn't act in the same direction at all times - aforementioned resisting on the inside tire).

 

[Bluemustang]

It's hard to put the changes of the superpro bushing into full context. That said, I did at one time had the FP springs and shocks that Tim has, and added the RLCA bearing afterward, so I do have some frame of reference. Then again that's looking back about 2 years ago. I've also been able to drive Tim's car a few times before he did any of those rear suspension mods.

All that aside, I did feel more articulation of the rear suspension. Ride was improved and it felt like the superpro bushing is adding more "cushioning" than the bearings. I went over some rough bumps at low speed and it handled it like a champ. The whole package Tim has feels like OEM sports car suspension. The proof showed itself by how much I enjoyed driving it. I would like to tell people that suspension is very important because you feel it everytime you drive the car. For me personally that's always worth it. Also, I expect to feel more "bounce" due to the OEM RLCA bushing replaced and he still has stock shock mounts - but I'm happy to report I didn't notice any of that.

 

[TeeLew]

Nothing stated incorrect.

The only issue I see with the on-axis stiffness (and the off-axis that can never be eliminated) is that when you think outside of just roll resistance, it's quite compromised. That stiffness acts not only in roll but in jounce. It also acts like a bar on the inside tire in roll, resisting the main spring that's trying to push the tire back into the road. All the downside of a bar, none of the upside (ride compliance). All downside of a spring, without the upside (ride rate & roll rate but doesn't act in the same direction at all times - aforementioned resisting on the inside tire).

It's a case of springs used in a parallel. If we consider static ride to be 'neutral', then the total single wheel rate might be "corner spring+bushing torsional stiffness= total K" in compression and "corner spring-bushing torsional stiffness=total K" in rebound. It will make the effective spring rate of the outer wheel stiffer and the inner wheel softer. An analogy might be setting the bump rubbers to engage in roll on the ouside of the car, but disengage on the inner wheels. Yes, it's different, because there's no second bump rubber which engages during rebound, but mathematically, it works out in a similar manner.

If we were running torsion bars for suspension springs, it might make this a little more intuitive. The difference with a torsion bar is they are set for zero deflection at full droop instead of zero deflection at static ride.

 

[TeeLew]

I have a different kind of problem. My race class allows delrin or oem rubber. It really sucks! I have always lathe cut and hand fit my own delrin bushings for standard A-arm wishbone suspensions. Can you guys envision what a "delrin" solution would look like that could provide the on and off axis movement of a spherical?

I've got some questions for you. What sanctioning body/class are you racing? What's the exact rule wording?

I'm doing some work on this and I may very well have a good alternative in not too long.

 

[fatbillybob]

I've got some questions for you. What sanctioning body/class are you racing? What's the exact rule wording?

I'm doing some work on this and I may very well have a good alternative in not too long.

The SCCA "T" racing classes allow Delrin, poly, and rubber. I hate rubber and poly. Delrin is almost like a spherical in some design applications. Sphericals work best and delrin 2nd for many reasons like hardness and self-lubricating nature and reasonably long lasting with good wear resistance. I honestly have not deconstructed an oem rubber busihing to figure out how to make it in delrin. But it sounds like the off axis will defeat a delrin design because of it's incompressibility and inability to yield. I bet you could meet the letter of the rule by using a johnny joint. That's what I need a shherical wrapped in delrin to meet the letter of the rule. I need that for all the suspect rubber joints in the suspension.

 

[TeeLew]

The SCCA "T" racing classes allow Delrin, poly, and rubber. I hate rubber and poly. Delrin is almost like a spherical in some design applications. Sphericals work best and delrin 2nd for many reasons like hardness and self-lubricating nature and reasonably long lasting with good wear resistance. I honestly have not deconstructed an oem rubber busihing to figure out how to make it in delrin. But it sounds like the off axis will defeat a delrin design because of it's incompressibility and inability to yield. I bet you could meet the letter of the rule by using a johnny joint. That's what I need a shherical wrapped in delrin to meet the letter of the rule. I need that for all the suspect rubber joints in the suspension.

OK, so legally speaking, the SuperPro bushing would be fine for you to run, but you're not a fan of Polyurethane. Got it. I'm working on something which will meet the letter of the law and be 95% as good as a spherical. It probably also won't be too bad on NVH or durability. Stay tuned.

 

[fatbillybob]

OK, so legally speaking, the SuperPro bushing would be fine for you to run, but you're not a fan of Polyurethane. Got it. I'm working on something which will meet the letter of the law and be 95% as good as a spherical. It probably also won't be too bad on NVH or durability. Stay tuned.

i'm in palos verdes and you in huntington beach so we are close. I do have a small manual lathe I have cut many delrin bushings for unequal length A-arm suspensions ( so simple shapes) and happy to help with the project.

 

[Norm Peterson]

I'm doing some work on this and I may very well have a good alternative in not too long.

Nothing stated incorrect.

The only issue I see with the on-axis stiffness (and the off-axis that can never be eliminated) is that when you think outside of just roll resistance, it's quite compromised. That stiffness acts not only in roll but in jounce. It also acts like a bar on the inside tire in roll, resisting the main spring that's trying to push the tire back into the road. All the downside of a bar, none of the upside (ride compliance). All downside of a spring, without the upside (ride rate & roll rate but doesn't act in the same direction at all times - aforementioned resisting on the inside tire).

Basically a step-change nonlinearity that we could well do without.


Norm

 

[Brian@BMVK]

Basically a step-change nonlinearity that we could well do without.


Norm

Yep. Thus why I feel like any car that sees some track use should look for an alternative here. I am feeling tempted to try the Superpro bushing. At $95 shipped, and knowing that it will be easier to press out my current bearings than the OEM bushing, it seems doable.

 

[buttsy]

The more I read. The more I wish I conducted some actual testing to measure the forces required to move the lower control arm up and down with the standard inner front bush and rear bearing installed when I had the shock and spring removed. And then repeated it with the front superpro bush fitted. It quite possibly would have put the binding debate to bed. lol.
I did physically feel the difference. With the standard rubber bush fitted, it obviously became exponentially harder to move the arm up or down the further it travelled. And when released from anywhere but the neutral position it would obviously spring back.
The superpro bush from memory moved far easier and didnt have the return to centre action. Obviously due to the poly bush being free of the centre metal sleeve.
I truly believe that the slight resistance added by the superpro bush vs a bearing is not even worth considering.
Due to the fact that it has a definite pivot point with approx a 550mm lever and 60lb's of weight acting on it. Not taking into account the spring, shock absorber, weight of the car etc etc.
The OEM rubber bush is a different story. The 550mm arm is attempting to twist the rubber inside the bush which is captive on both the inner and outer. I still believe that the forces will be negligible due to the small amount of rotation needed. Which I cant imagine would be much more than 10 degrees.
Anyway. Could someone do some real world testing please. Before removing the inner control arm mounts and with the spring and shock removed. Put a small crane scale on the outer point of the control arm and measure the kg's or pounds required to move the arm to different heights.
The superpro bush needs a different test, due to the force being fairly linear. Something that can measure force/time. But crane scales raised at a fairly consistent slow speed will give a rough idea.
Hope this makes some sense. lol.

 

[TeeLew]

i'm in palos verdes and you in huntington beach so we are close. I do have a small manual lathe I have cut many delrin bushings for unequal length A-arm suspensions ( so simple shapes) and happy to help with the project.

I'm not going to be actually making them, but I think I've found an option. I'm chasing this down, because it's good for pretty much all of us.

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