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      04-04-2022, 08:37 PM   #1
Coi
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Do Aftermarket (Polyurethane) FCABs Improve Steering Feel? (Esp on E36/E46/E85/E86)

I made a thread about this on ZPost but with the regular E85 Z4 having an electric rack and the Z4M being a very rare car I didn't get any responses. I've seen several posts across forums about the pros/cons of poly front control arm bushings but none specifically about steering feel.

I've owned by Z4M for several months and have been very happy with it in almost every single way except for the steering feel. While it's better than any electric rack I've driven and certainly has feedback, it's still not on the same level as the E93 I used to have or my buddy's low-mileage 987.2 Cayman. My FCABs show some signs of wear/age but I don't think they're totally shot because turn-in is still precise and the car does not wander.

I was thinking of just replacing these with new OEM offset rubber bushings, but wondered if anyone saw improved steering feel with aftermarket polyurethane FCABs. I know the primary reason people upgrade these is to decrease deflection on track, but are they worth the downsides (harshness, potential noise) on a street car for improvement in road feel?

If anyone is interested, these are the options I'm considering:

New OEM BMW rubber offset bushings for Z4M (31107838575) ~$60
Could get them pre-pressed into lollipops from a forum member ~$120

Whiteline caster bushing set, polyurethane (W52606) ~$60
I know this company is relatively reputable but I can't find any reviews of their FCABs on any BMW, let alone the offset ones, so that does give me some hesitation. Price is good.

Powerflex 66 mm offset bushing, aluminum/polyurethane (PFF5-5601G) ~$220
These are the most aggressive option being mostly aluminum, and are several times the price of the others. Some people report noise from these as well as an increase in ride harshness. They're pretty commonly used by forum members through on various models.


I know there are other factors that affect steering feel like alignment and tires (I have factory alignment specs and Michelin PS4S right now), but I figure if I'm replacing FCABs I should get the best option.

Thanks!
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      04-09-2022, 06:37 PM   #2
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Standard rubber has hardness 55-60 (+/- 5) ShA
The most popular polyurethane (PU) in the market are PU 75 ShA and PU 90 ShA.
So PU is harder than rubber in 35-60%.
It's has lower friction coefficient and it is much more long-lasting material.
But it also has squeak in humidity and can be broken more easily.

So there is no clear answer with benefits of use just for simple driving
(while professionals use it widely in race).
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      04-09-2022, 10:36 PM   #3
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Quote:
Originally Posted by Coi View Post
I made a thread about this on ZPost but with the regular E85 Z4 having an electric rack and the Z4M being a very rare car I didn't get any responses. I've seen several posts across forums about the pros/cons of poly front control arm bushings but none specifically about steering feel.

I've owned by Z4M for several months and have been very happy with it in almost every single way except for the steering feel. While it's better than any electric rack I've driven and certainly has feedback, it's still not on the same level as the E93 I used to have or my buddy's low-mileage 987.2 Cayman. My FCABs show some signs of wear/age but I don't think they're totally shot because turn-in is still precise and the car does not wander.

I was thinking of just replacing these with new OEM offset rubber bushings, but wondered if anyone saw improved steering feel with aftermarket polyurethane FCABs. I know the primary reason people upgrade these is to decrease deflection on track, but are they worth the downsides (harshness, potential noise) on a street car for improvement in road feel?

If anyone is interested, these are the options I'm considering:

New OEM BMW rubber offset bushings for Z4M (31107838575) ~$60
Could get them pre-pressed into lollipops from a forum member ~$120

Whiteline caster bushing set, polyurethane (W52606) ~$60
I know this company is relatively reputable but I can't find any reviews of their FCABs on any BMW, let alone the offset ones, so that does give me some hesitation. Price is good.

Powerflex 66 mm offset bushing, aluminum/polyurethane (PFF5-5601G) ~$220
These are the most aggressive option being mostly aluminum, and are several times the price of the others. Some people report noise from these as well as an increase in ride harshness. They're pretty commonly used by forum members through on various models.


I know there are other factors that affect steering feel like alignment and tires (I have factory alignment specs and Michelin PS4S right now), but I figure if I'm replacing FCABs I should get the best option.

Thanks!
The FCABs wear our very quickly on the Z4M (owned one for 12 yrs)
This is primarily due to the bushing being offset which leads to very little bushing rubber on one side.
You should be able to inspect and see if there are breaks & cracks in the bushing rubber material.

The Z4M has amazing steering feel when everything is in good shape, so you must have something going on with yours.
Also be sure to check other control arm bushings/bearings , tie rods etc.
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      04-11-2022, 09:10 AM   #4
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I've installed powerflex purple on the regular Z4 shortly after I got the car but at the same time I've also installed ST X coilovers. Before this the original suspension was completely shot and drove like crap. It was all over the place, harsh, unstable, just terrible. So these upgrades made a massive difference and steering is direct, responsive and sharp. It goes where you point it. I am sure poly fcabs contribute but its hard to say exactly how much though. I don't detect any additional NVH.

Z4M is in a whole different category as far as steering goes. It overall feels like a completely different car to begin with. Personally went with oem fcabs on this car. Its already very quick and sharp out of factory. Didn't think there's need to mess around here. No regrets.

OP, have you changed the RTABs yet? If not, I would highly recommend you do. OEM + RTAB limiters is good option. It will tighten up the rear. Alignment is required after that job.

Last edited by belcom; 04-11-2022 at 09:16 AM..
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      05-03-2022, 08:05 PM   #5
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Quote:
Originally Posted by manija View Post
Standard rubber has hardness 55-60 (+/- 5) ShA
The most popular polyurethane (PU) in the market are PU 75 ShA and PU 90 ShA.
So PU is harder than rubber in 35-60%.
It's has lower friction coefficient and it is much more long-lasting material.
But it also has squeak in humidity and can be broken more easily.

So there is no clear answer with benefits of use just for simple driving
(while professionals use it widely in race).
Thanks for the reply! I agree that the poly FCAB will have no performance benefit for street driving. I'm mainly looking for an improvement in subjective feel. An increase in durability would be nice too.
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      05-03-2022, 08:11 PM   #6
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Quote:
Originally Posted by inTgr8r View Post
The FCABs wear our very quickly on the Z4M (owned one for 12 yrs)
This is primarily due to the bushing being offset which leads to very little bushing rubber on one side.
You should be able to inspect and see if there are breaks & cracks in the bushing rubber material.

The Z4M has amazing steering feel when everything is in good shape, so you must have something going on with yours.
Also be sure to check other control arm bushings/bearings , tie rods etc.
I haven't personally laid eyes on my FCABs but while my mechanic was doing my VANOS he looked at them and said they were 'showing signs of wear but not shot' or something along those lines. I have checked tie rods and those have no slop or movement whatsoever.

All of the suspension on my car seems original, so some of the rubber is definitely tired after 15 years and 80k miles. Based on your reply and others I think my steering feel isn't as good as it should be, even if there isn't slop during turn-in. I don't have any records of anything being replaced so FCABs and RTABs are on the table.
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      05-03-2022, 08:17 PM   #7
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Quote:
Originally Posted by belcom View Post
I've installed powerflex purple on the regular Z4 shortly after I got the car but at the same time I've also installed ST X coilovers. Before this the original suspension was completely shot and drove like crap. It was all over the place, harsh, unstable, just terrible. So these upgrades made a massive difference and steering is direct, responsive and sharp. It goes where you point it. I am sure poly fcabs contribute but its hard to say exactly how much though. I don't detect any additional NVH.

Z4M is in a whole different category as far as steering goes. It overall feels like a completely different car to begin with. Personally went with oem fcabs on this car. Its already very quick and sharp out of factory. Didn't think there's need to mess around here. No regrets.

OP, have you changed the RTABs yet? If not, I would highly recommend you do. OEM + RTAB limiters is good option. It will tighten up the rear. Alignment is required after that job.
Yeah, the strange part is I don't have any issues with the directness of the steering or instability of the car. I think it's really just subjective feel that's not up to snuff. The Z4M does have hydraulic steering compared to the electric in the regular Z4 so I certainly would expect a big difference there, even compared to a modified regular car. The M also has a much quicker steering ratio. I've never driven a non-M Z4 personally though. Right now I'm going back-and-forth between new OEM Z4M FCABs and the offset whiteline ones.

I haven't changed RTABs and they need to be done; they appear to be original. I have Lemforder (basically OEM) bushings and limiters sitting in my garage waiting to be installed. Will get a full custom alignment after that.
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      05-04-2022, 08:59 PM   #8
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Quote:
Originally Posted by Coi View Post
I haven't personally laid eyes on my FCABs but while my mechanic was doing my VANOS he looked at them and said they were 'showing signs of wear but not shot' or something along those lines. I have checked tie rods and those have no slop or movement whatsoever.

All of the suspension on my car seems original, so some of the rubber is definitely tired after 15 years and 80k miles. Based on your reply and others I think my steering feel isn't as good as it should be, even if there isn't slop during turn-in. I don't have any records of anything being replaced so FCABs and RTABs are on the table.
Front lower control arm bushings are also something that goes.

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      05-10-2022, 01:21 AM   #9
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Poly isn't a good material for FCABs. Too many people who install them see premature failures soon after to ever make this recommendable.

Try putting in some fresh OEM ones first, and if that still isn't enough then look at some delrin ones or Turner monoball. As stated above OEM bushings don't last long so it's best to just change them (and RTAB) as a maintenance item every 25-30k mi if you want to maintain feel without adding NVH
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      05-10-2022, 03:50 AM   #10
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Quote:
Originally Posted by jvit27 View Post
Poly isn't a good material for FCABs. Too many people who install them see premature failures soon after to ever make this recommendable.
Potentially only on track, with soft ones.

I've had powerflex fcabs for 12 years (roughly 50k miles), which is probably longer than most here, and they are still as new and still have that new feel. NVH is comparable to brand new OEM bushings
So for street use they are very very well suited. Far better than OEM rubber.

Delrin or monoballs is much much harder than PU
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      05-11-2022, 12:32 AM   #11
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Quote:
Originally Posted by GuidoK View Post
Potentially only on track, with soft ones.

I've had powerflex fcabs for 12 years (roughly 50k miles), which is probably longer than most here, and they are still as new and still have that new feel. NVH is comparable to brand new OEM bushings
So for street use they are very very well suited. Far better than OEM rubber.

Delrin or monoballs is much much harder than PU
Maybe you haven't read much about them over the years, but you're one of the lucky ones. My Powerflex fcab's failed within 700 miles. Plenty of others have similar experience without having to go to the track - specifically with Powerflex. And most who go *back* to OEM rubber are much happier for street use.

Additional downsides to poly are them drying up and being squeaky. So this requires maintenance. Thus I say, if OEM rubber are still too soft then go all the way and get the monoball or delrin. They are harder but also less likely to fail.
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      05-11-2022, 05:52 AM   #12
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Quote:
Originally Posted by jvit27 View Post
Maybe you haven't read much about them over the years, but you're one of the lucky ones. My Powerflex fcab's failed within 700 miles. Plenty of others have similar experience without having to go to the track - specifically with Powerflex. And most who go *back* to OEM rubber are much happier for street use.
Lots of people use powerflex here over in europe for many years on end.
Go and look on the german forums for user experiences.
I only read this from US user experiences. And having installed them 12 years ago 50k miles, following most developments of most manufacturers, I'd say I've read more about them than most people.

And I don't think it's a matter of luck; my car is completely polybushed, so that's what? 22 bushings or so? and they're still all in pristine order, no squeaks etc.
That can't be luck. It's either an installment issue or something else. But not luck.

Quote:
Additional downsides to poly are them drying up and being squeaky. So this requires maintenance. Thus I say, if OEM rubber are still too soft then go all the way and get the monoball or delrin. They are harder but also less likely to fail.
After 12 years still no squeak. Must be an installment fail issue then.
I mean, if they don't squeak after 12 years and 50k miles....I must have done something right
This is considerably longer than the average OEM bushing holds, and the poly bushing keeps it's feel, it's just as solid as from day one. The OEM ones failed after 6 years or so.

So with the amount of miles I have on mine, and I do a decent amount of pretty hard mountain pass driving in the alps, so they're not pampered, I can only conclude that they're way better than OEM.
For track use Powerflex have the black series.
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Last edited by GuidoK; 05-11-2022 at 06:04 AM..
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      06-17-2022, 03:45 PM   #13
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Quote:
Originally Posted by jvit27 View Post
Maybe you haven't read much about them over the years, but you're one of the lucky ones. My Powerflex fcab's failed within 700 miles. Plenty of others have similar experience without having to go to the track - specifically with Powerflex. And most who go *back* to OEM rubber are much happier for street use.

Additional downsides to poly are them drying up and being squeaky. So this requires maintenance. Thus I say, if OEM rubber are still too soft then go all the way and get the monoball or delrin. They are harder but also less likely to fail.

I've been pre-pressing FCABs for various BMWs as a forum offering for a good 12 yrs or so and know the topic well. Jvit27 speaks the truth. If you have a daily driver used for everyday driving, poly FCABs will be fine. However, if you have do track days and/or drive hard, the heat from the close proximity of the exhaust manifold will take it's toll .

Folks can PM me if they're looking for OE offset rubber pre-pressed in.
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