RLCA Help: Spherical Bearing vs. Poly Bushing

[Brian@BMVK]

I’m thinking along the same lines. I love the way the car feels on the bearings, but if they’re going to need replacing at that frequency I’ll opt for the poly bush next time around. Not having to remove the RLCA‘s every couple of years has a certain appeal.

As would a little bit of OEM feel over choppy surfaces. The handling with the bearings is 100% worth it though. I suspect I would not notice much difference with the bushings, even with my sensitive butt.

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[Norm Peterson]

As would a little bit of OEM feel over choppy surfaces. The handling with the bearings is 100% worth it though. I suspect I would not notice much difference with the bushings, even with my sensitive butt.

I have my doubts you would, too. Once the modulus gets to the 700 mPa / 100,000 psi range (about where I think bushing polyurethanes fall), there isn't going to be much deformation left for a still stiffer material to reduce.


Norm

 

[TeeLew]

One reason I'm a little apprehensive about sphericals is that it puts a lot of vibration through the tub mounts which eventually tend to form cracks. Having *some* sort of bushing in there helps take that high frequency content out of the equation.

 

[GT 550]

@TeeLew hey Tim any further thoughts on the bushings after a couple of weeks?

 

[TeeLew]

@TeeLew hey Tim any further thoughts on the bushings after a couple of weeks?

Tl;dr: This change is a performance gain with a noticeable loss in road insulation, but it's good on its NVH/Performance ratio.

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I had a 150 mile round trip with the wife 2 weekends ago & a 400 miler for work last weekend. There is definitely a less insulated feeling about the car. It's a tick louder, but not much and not enough to bother me (my wife didn't comment, either). It doesn't seem to change the kickback through the steering over rough pavement or bumps, but it has more feeling in the wheel, which is a little difficult to describe.

In terms of handling, it's a very noticeable change. Response is crisp & it seems limit grip is up a little. The biggest difference is its how it has increased response. People overuse the term razor-sharp, it's too big of a car for that, but it feels directly connected to the road. The downside is it wants to follow the road a little too much and if you don't have relatively calm hands, the car might be a little darty on the freeway. After you make the changes, it's not tough to understand why they don't make the car this way from the factory. It might be annoying if you didn't specifically want it. I'd say it's 80% of the way to a monoball suspension with less NVH and much better longevity.

I've only done one autocross, and the car performed better than I did. It accepted being chucked and slid around without ever really biting me. I think with the stock rubber bushings would have been more vague, less stable & slower.

For the record, I've changed every bushing in the car except for the rear outboard toe bushing (it will happen soon) and the car has about 2200 miles, so everything is still really fresh. I still plan to put stiffer rear springs (& softer rear bar) on the car, but it is getting a little bit on the racy end of everyday drivability.

 

[Brian@BMVK]

After you make the changes, it's not tough to understand why they don't make the car this way from the factory. It might be annoying if you didn't specifically want it.

I think most of what you're describing is coming from the front regarding tramlining/dartiness.

As you changed all bushings, it's impossible to distinguish the effect of just one. For what it's worth, changing the rear LCA bushings to bearings mainly added noise when it came to negatives, and only from sharp road impacts. This change was with previously installed CB005 and spherical shock mounts, but no other bushing changes at the rear. I do think that I may change to something like the Superpro bushing down the road to get the vast majority of the performance improvement with a bit more refined ride. It should be much easier to press out the bearings than the OEM bushings, as the fit isn't as tight.

 

[TeeLew]

I think most of what you're describing is coming from the front regarding tramlining/dartiness.

As you changed all bushings, it's impossible to distinguish the effect of just one.

I completely agree. Along with the bushings, I'm running a different alignment on the front, so it *should* feel responsive. One man's 'nimble' is another man's 'nervous'.

It would have been interesting to change the bushings one at a time to evaluate each, but that's not really my M.O.. I'm kinda a 'both feet in' type.

I will say that the subframe/differential bushings probably added more cabin noise than the suspension, but the suspension bushings you feel more through the wheel. If you're going for performance, though, I think both are important.

 

[Radiation Joe]

I just ordered the whiteline KDT953 subframe bushing replacements and the KDT933 diff bushing replacements. While the subframe is out for these installs, I intend to replace the RLCA bushing. It's between the BK055 and the Superpro.
I know it's subjective, but how are folks leaning with regard to feel between the two set-ups? Can I really only count on 15k-20k miles before the BK055s start making enough noise to be a problem? I drive year round in the northeast. Are the BK055s going to provide enough better feel/accuracy and are the Superpros going to make noise (Poly squeaks) as-well after 15k miles. I think I'd prefer a minor rattle over a poly squeak. Really on the fence.

 

[fatbillybob]

Joe,

My opinion is stick to oe rubber. I'm race only and been lazy taking the final step of my race class legal changes to the bushings. I'm actually surprised the rubber works as well as it does. You just most likely are going to see no street advantage. On track yes but I m not even in a hurry to make the change as my control arm parts sit in a box in the garage.

 

[moffetts]

I don’t recommend any aftermarket diff bushings or lockouts. They will add NVH, guaranteed. The KDT933s add more NVH than all of my other mods combined, including all of the spherical bearings.

 

[galaxy]

Just because I've been researching this topic to the point that I have a headache, LOL....it certainly seems like the Superpro(usa?) bushing are the way to go for the average Joe that want's to do some tasteful mods. As an average Joe, I would not be a fan of replacing a bearing every so often. Great guys.

On a side note...anyone else notice the overwhelming similarities between Superprousa's website and whiteline?

 

[TeeLew]

I don’t recommend any aftermarket diff bushings or lockouts. They will add NVH, guaranteed. The KDT933s add more NVH than all of my other mods combined, including all of the spherical bearings.

Blanket statements like this are useless. It depends on one's goals if it's a good trade-off or not. The BMR red poly diff puck kit and red poly rear subframe bushing add a minor amount of NVH and provide a noticeable difference in the handling response of the chassis. Only you can determine if the juice is worth the squeeze for you.

 

[moffetts]

Blanket statements like this are useless. It depends on one's goals if it's a good trade-off or not. The BMR red poly diff puck kit and red poly rear subframe bushing add a minor amount of NVH and provide a noticeable difference in the handling response of the chassis. Only you can determine if the juice is worth the squeeze for you.

I didn’t tell him not to do it, I told him that I don’t recommend it having done it myself. The KDT933s are effectively a one way street; if you don’t like the NVH that will 100% be noticeable, you’re screwed unless you buy a new subframe.

 

[Norm Peterson]

Stiffening up the differential bushings sounds like a mod you'd do for drag racing where clutch engagements would normally be much harsher than in HPDE, time trialing, or autocross (drag-race-start Pro-Solo perhaps excepted).

The hub carriers are isolated from the pumpkin by pairs of universal joints so I'm not seeing a lot of crosstalk between pumpkin deflections and suspension reactions like there is with the S197's stick axle where the suspension is what locates the pumpkin.


Norm

 

[Radiation Joe]

I'm committed to the subframe bushings and diff bushings. I'm fairly comfortable with increases in NVH to a point. That's why I'm not going with the delrin or aluminum subframe bushings or the diff kits from BMR or Steeda. The Whiteline diff kit is not well known but I've read here that it is not as significant a source of NVH compared to the Steeda and BMR kits. I could be wrong. I'll comment after install.
I'm leaning towards the BK-055 bearing vs the Superpro bushing.

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