[bmw_solid]

Hi All,

Where are people buying these from? BMW Dealer or Aftermarket OEM? If OEM, then who makes them and what's the Part Number?

What is the sacrifice compared to the standard hollow OEM E90 RSFB? NVH? COMFORT? OR IS THERE NONE?

Who has fitted these to a standard E90 LCI M-SPORT with OEM suspension? Did you see a great difference in handling?

WHY does no body ever fit STANDARD BMW E90 RSFB to their standard E9x when replacing RSFB? Doesn't M3 RSFB put extra load on OEM suspension? ARE M3 RSFB Bushings COMPATIBLE with OEM suspension tuning?

Would you say the M3 RSFB compromises comfort in any way, shape or form?

My CAR:

2010 E90 320d Manual with ALL NEW OEM BILSTEIN B4 SPORTS SHOCKS x4 and ALL NEW OEM SACHS D3 (front) and D4 (rear) SPRINGS.
X4 FALKEN FK520 BRAND NEW TYRES

NO MODS ON VEHICLE.

COMPLAINT: Handling is vaguely loose at rear, body roll is present and understeer characteristics present (at all pressures, 34,34 or stated 33 39). New Springs and shocks and mounts didn't help much with handling, but the alignment did but not a lot.

So now i'm thinking, the CULPRIT has got to be the RSFB surely?

COMPLAINT 2: COMFORT is ok but the rear of the car feels underdamped in the sense of quick jolty bump absorption compared to the front, which is a bit more floaty rather than jolty.

COMPLAINT 3: THIS IS WIERD. But some days, (note minimal temperature difference in weather) the car will handle compliantly (but still not sharp or as good a a BMW should) and also give less jolty bumps at the rear BUT SOME DAYS the car would drive like a dog, quite unpleasant.... comfort and handling feels off. ALMOST LIKE THE CAR HAS A ELECTRONIC SUSPENSION SYSTEM WHICH SOMEDAYS WORKS FINE AND SOME DAYS DOESN'T

DESIRE: GET MY E90 TO HANDLE SHARP AND PRECISE LIKE FACTORY AND IMPROVE REAR COMFORT/BUMP ABSORPTION (i feel the original RSFB are shot and allow excessive movement during bumps).

Thank You,

[whyzee125]

The biggest issue with e90 suspension, is that they're undersprung and underdamped from the factory as they designed the whole suspension around the crappy runflat tires of 2007. The only way to make them ride decently on those tires, was to make the suspension softer than BMW usually has in the past generations.

If your RSFB's are torn/worn out, I'd imagine that could cause too loose of a rear end but I've never really seen that. People generally upgrade them because they are getting a lot of wallowing under WOT at high power levels. I don't imagine that's a concern with a 320d.

The M3 RSFBs do increase NVH somewhat but not a huge amount. I have full solid aluminum in the rear of mine and while I do somewhat regret it, the NVH is not bad.

I would go AKG 95a poly if I were to do it again.

The stock ones do soften the ride somewhat as the subframe is 'suspended' in the rubber but it really doesn't allow much up and down movement, just enough to dampen hard impacts a tad.

If your car is holding alignment, I'd imagine most of your rear bushings are good. you can remove the little push rods and get a gander at your RSFBs but unless they're super dried out or your car has a lot of miles I'd imagine they will be in decent shape. I think the issue is the soft stock suspension. A set of Koni yellows would do wonders to making the car feel more confident on its feet.

[bmw_solid]

Originally Posted by whyzee125

The biggest issue with e90 suspension, is that they're undersprung and underdamped from the factory as they designed the whole suspension around the crappy runflat tires of 2007. The only way to make them ride decently on those tires, was to make the suspension softer than BMW usually has in the past generations.

If your RSFB's are torn/worn out, I'd imagine that could cause too loose of a rear end but I've never really seen that. People generally upgrade them because they are getting a lot of wallowing under WOT at high power levels. I don't imagine that's a concern with a 320d.

The M3 RSFBs do increase NVH somewhat but not a huge amount. I have full solid aluminum in the rear of mine and while I do somewhat regret it, the NVH is not bad.

I would go AKG 95a poly if I were to do it again.

The stock ones do soften the ride somewhat as the subframe is 'suspended' in the rubber but it really doesn't allow much up and down movement, just enough to dampen hard impacts a tad.

If your car is holding alignment, I'd imagine most of your rear bushings are good. you can remove the little push rods and get a gander at your RSFBs but unless they're super dried out or your car has a lot of miles I'd imagine they will be in decent shape. I think the issue is the soft stock suspension. A set of Koni yellows would do wonders to making the car feel more confident on its feet.

I test drove a 2010 E90 320d M-Sport with 92k miles on it (before purchasing my E90) and it was a local dealer so I drove it around the same roads where I commute and drive. The pressure was 33/34 cold all round and it was running standard tyres. To be frank, the car drove EXCELLENT! It was comfortable, not very crashy, well damped and handled really nice! A bit of squash on turns but NO BODY ROLL. I then went on and brought my E90 which had runflats so I ditched them for the FK520s standard tyres in hope that my E90 would drive like the test drive vehicle but it doesn't even after spending £750 in parts on OEM suspension components + tyres.

So I'm not led to believe that runflats or standards actually affect the ride that much. Even the dealer, who sold mainly BMWs said the same thing. He said runflats make it a bit harsher and that's all.

So I believe that it can only be the RSFB that are stopping my car from driving like a BMW should.

I can't think of the poly bushings because I've heard good and bad of them. NVH in particular is known to be bad with poly bushings + OEM M Suspension surely can't cope with such rigid bushings??

I'm just trying to get my E90 to drive like how it did from the Factory - that's all. I have new shocks, springs and mounts and Performance tyres so what more could it be? RSFB right? Hence why I don't see the point of B8s or Konis etc - they seem to be enhancement of a already excellent handling car, which I don't need and doesn't justify the massive costs and un-true OEM ride and handling comapred to factory.

[The Nightman]

On a street car, I would just do the poly inserts. Cheap, easy to install and good results.

[Tambohamilton]

I'm happy with my M3 rsfb. Would do it again. Small increase in noise, probably - mainly diff noise. Sorted out tramlining and vagueness for me.

A lot of people on here their main complaint is squirming under acceleration etc, but the rsfb literally attach the rear wheels to the chassis so if they aren't reasonably firm they will cause vagueness etc. Stock bushings are really soft and designed to induce understeer, so they're a definite weak point.

You could go with something firmer than the M3 ones, but it's probably not really useful outside of track use. Also M3 are probably cheaper.

Lemforder are the OEM. Get them from autodoc, probably. Mine have the M3 logo ground off, so likely the same part as genuine. Realoem.com for part numbers. Pay attention to the orientation of the M3 bushings - it's not the same as stock. Get some rubber lubricant for the assembly too; https://www.cromwell.co.uk/shop/lubr.../p/CTL7406447E - I believe that's the same stuff as BMW use.

[bmw_solid]

Originally Posted by The Nightman

On a street car, I would just do the poly inserts. Cheap, easy to install and good results.

Not sure if this is what I'm after, as I want to restore factory drive rather than put a plaster over possibly shot factory RSFB.

[bmw_solid]

Originally Posted by Tambohamilton

I'm happy with my M3 rsfb. Would do it again. Small increase in noise, probably - mainly diff noise. Sorted out tramlining and vagueness for me.

A lot of people on here their main complaint is squirming under acceleration etc, but the rsfb literally attach the rear wheels to the chassis so if they aren't reasonably firm they will cause vagueness etc. Stock bushings are really soft and designed to induce understeer, so they're a definite weak point.

You could go with something firmer than the M3 ones, but it's probably not really useful outside of track use. Also M3 are probably cheaper.

Lemforder are the OEM. Get them from autodoc, probably. Mine have the M3 logo ground off, so likely the same part as genuine. Realoem.com for part numbers. Pay attention to the orientation of the M3 bushings - it's not the same as stock. Get some rubber lubricant for the assembly too; https://www.cromwell.co.uk/shop/lubr.../p/CTL7406447E - I believe that's the same stuff as BMW use.

Ok, and what are you running on? Stock or OEM suspension or high performance equipment? Are you running standard tyres right?

Do the M3 RSFB firm up the ride or do they maintain Stock comfort?

Stock bushings are perfect for everyday city use and spirited driving every now and then because I test drove a E90 and it was just perfect but not as sharp as a M car which I understand. Obviously the M3 ones are for enhanced handling at high loads which I'm not after but I wouldn't mind the M3 ones as long as they don't affect COMFORT over Stock, which is my top priority

Yes, I would never go out of Factory Constraints and look for poly or alu bushings, only Stock or M3 bushings.

Thanks for confirming - so its is good old Lemforder who make the M3 RSFB! I'll assume Lemforder make the Stock E90 bushings too then?

Ultimately, I wouldn't mind sharper handling and slightly, I repeat, Slightly more NVH with the M3 ones, but I can't compromise on the already firm comfort.

Lastly, I'm skeptical of whether or not the M3 ones go well with stock suspension. Many here are using B6 and higher shocks, lowering springs or Konis etc etc with M3 RSFB but I want to hear feedback from people who've done this mod on STOCK suspension.

[Tambohamilton]

My suspension isn't stock, but it's not a million miles from stock either; when I did the M3 rsfb initially it was stock other than those and koni special active shocks. My assessment of it was more noise (mainly the diff), no more wobbly back end. Can't say I noticed any increase in V or H.

[bmw_solid]

Originally Posted by Tambohamilton

My suspension isn't stock, but it's not a million miles from stock either; when I did the M3 rsfb initially it was stock other than those and koni special active shocks. My assessment of it was more noise (mainly the diff), no more wobbly back end. Can't say I noticed any increase in V or H.

How would you quantify the extra whine from the diff? 10%, 20% etc??
Would you say it's worth replacing the diff mounts with STOCK mounts to stop the extra whine? Are the diff mounts different on M3 E90?

What was your verdict on comfort? Did it remain the same, decrease or increase? If so, by what percentage?

I'm really tempted to go for M3 RSFB because they don't cost much more than STOCK. But I'm concerned mainly about comfort. I know they'll bring magic to the handling but the Stock RSFB are also great for handling whilst maintaining optimum comfort so can the M3 ones maintain comfort too?

I'm not a track guy and neither am I concerned about WOT under acceleration - I just want no body roll, feedback from steering + (as a bonus) sharpness too, but sharpness is not essential as Its a family car and I don't want to compromise on comfort.

See post #90 here:
https://www.e90post.com/forums/showt...1970912&page=5

He says the Stock suspension felt and drove great and I too experienced this on a 92k miles 320d E90 LCI on standard tyres. So the question is, will installing the M3 ones be really worth it if Stock is already so good?

[Tambohamilton]

Couldn't hear the diff whine before, can hear it now. Maybe my diff is just ducked though.

I didn't notice any difference in comfort, but I spend almost zero time in the back of my car.

If you're happy with stock, stay with stock. If you're not happy, go M3 safe in the knowledge that nothing about it will be bad.

[BB_cuda]

Read through whole thread.

OP, to get less butt wiggle during hard acceleration, you need to go with the M3 RSFB. They are still rubber (like your normal E90 bushings) but more of in the webbing within the bushing. The insets sort of accomplish filling in the gaps to get you about to same M3 stiffness. My car has polyurethane RSFB. I’ve ridden in an M3 and it was more compliant. Please feel assured this is right thing to do.
I do regret going to polyurethane diff bushings. I’m hearing diff whine. My Wavetrac LSD (with 335D torque) is a blast though.

[bmw_solid]

Originally Posted by Tambohamilton

Couldn't hear the diff whine before, can hear it now. Maybe my diff is just ducked though.

I didn't notice any difference in comfort, but I spend almost zero time in the back of my car.

If you're happy with stock, stay with stock. If you're not happy, go M3 safe in the knowledge that nothing about it will be bad.

Apologies for the late response.

Its a shame it promotes diff whine. If I do go for the M3 RSFB route, then I'll be tempted to replace the diff mounts to Stock mounts plus a fluid replenish to retard any chances of diff whine.

Interesting, I though it would affect overall comfort as well as rear comfort too. Maybe I'm wrong.

Well, I can't comment on the stock mounts because I'm sure mine are shot as I've replaced springs and shocks and no improvement on handling.
But the test drive of a 2010 E90 M Sport assuming it was on Stock mounts performed really well from a comfort to handling ratio.

[bmw_solid]

Originally Posted by BB_cuda

Read through whole thread.

OP, to get less butt wiggle during hard acceleration, you need to go with the M3 RSFB. They are still rubber (like your normal E90 bushings) but more of in the webbing within the bushing. The insets sort of accomplish filling in the gaps to get you about to same M3 stiffness. My car has polyurethane RSFB. I’ve ridden in an M3 and it was more compliant. Please feel assured this is right thing to do.
I do regret going to polyurethane diff bushings. I’m hearing diff whine. My Wavetrac LSD (with 335D torque) is a blast though.

Thank you for your input. Yes I am aware the Stock mounts have hollow voids and the M3 are rubber all over.

Yes they will stiffen up the handling but what I don't want is to stiffen the comfort.

I installed the Monroe Rubber upper rear shock mounts in the summer and they made the ride disgustingly firm and back breaking!! So I took them off and put OEM Lemforder foam mounts back on.
If the M3 RSFB will make this same effect like the Monroe Uppers did, I'd be gutted!!!!

Yes the Poly or aluminium stuff is way more than what i require so I won't look into them.

[bmw_solid]

Am I correct to say that, if the E90 was designed with STANDARD tyres, they would have used rubber RSFB mounts? As the M3 used STANDARD tyres from factory and stock E90 used RUNFLATS right??

Is it basically the rule of thumb that: If you want to put STANDARD tyres on a E90, then go for M3 RSFB because they'll remove the squat and squish and stiffen up the handling without affecting comfort? If you want to keep RUNFLATS then stick with STOCK RSFB?

[Tambohamilton]

Those things probably balance each other out to some extent, but I don't think it's a 100% correlation. There are other rubber bushings Vs ball joints etc in the suspension, whic differ between e9x and M3, and of course have an affect on nvh and handling

[bmw_solid]

Originally Posted by Tambohamilton

Those things probably balance each other out to some extent, but I don't think it's a 100% correlation. There are other rubber bushings Vs ball joints etc in the suspension, whic differ between e9x and M3, and of course have an affect on nvh and handling

I understand your point.

I was looking at a reputable Youtubbe channel of a guy who owns a hi-fi mechanic shop and specialises in BMW performance upgrades. He had a 125k+ miles E92 M3 LCI and in the end he said it was the RSFB that brought the vehicle back to factory handling feel.

My experience is leading me to make me believe in his findings. I've refreshed all shocks springs and mounts (no arms front or rear) and it made 10 or 20% improvement in handling. I was surprised!

I don't think arms make much of a difference - i changed them on me E92 330d SE Lemforder OEM + shocks and springs and mounts but again, not much improvement in handling or feel.

I think its the RSFB that actually bring these E9x cars to factory handling feel.

I'm still confused on M3 or STOCK RSFB
I know handling will be great but comfort is my worry.

[Tambohamilton]

Go M3 and don't look back. If nothing else, they'll last longer due to flexing less.

[bmw_solid]

Right, so I just rang around and spoke to 3 BMW specialists in my city, one of which is a highly rated and reputable garage and I've seen their site in person too.

They all said they've never come across M3 RSFB in a E9x and neither have they fitted M3 RSFB into E9x models. They've only ever used Stock RSFB replacements.

The first garage did mention they have fitted poly bushings but never M3 bushings.

It seems here in UK people don't usually fit M3 RSFB into their E9x models.
The UK Roads are poor I must say and maybe people don't want to stiffen up the already stiff ride hence why they get Stock bushings fitted instead.

And I understand the M3 RSFB are a pita to fit - some claim breaking the bushings, others claim needing a Hydraulic Press and some have reported bending the hollow metal around the aperture.
I can already see it. I drop my car off with M3 RSFB and the mechanic will call me 1.5 hrs later saying they're the wrong parts- they don't fit! What's the odds 😏. The mechanic wouldn't attempt further I know it.

[Tambohamilton]

Yeah, I bent mine a bit...but then I'm working under the car with a crappy press set (no hydraulics) and not even the correct lube. So long as the mechanic is competent there shouldn't be an issue. Fitting these bushings to a non-M is identical to fitting them to an M, in terms of the install process, so it's not an obscure process.

[Tambohamilton]

It seems like you want to put stock bushings back in there... Best get on with it! Anything will be better than aged, cracked rubber!

[bmw_solid]

Originally Posted by Tambohamilton

Yeah, I bent mine a bit...but then I'm working under the car with a crappy press set (no hydraulics) and not even the correct lube. So long as the mechanic is competent there shouldn't be an issue. Fitting these bushings to a non-M is identical to fitting them to an M, in terms of the install process, so it's not an obscure process.

Yes but some mechanics are very impatient/incompetent and they use the excuse of "We can't risk damaging your car any further and therefore won't attempt to install a part that doesn't want to fit easily." and they deny the job.

The BMW specialists are charging circa £300 labour for the job and I have a local mechanic who I use for normal jobs and he can do the job at his rate of £100 (3 hrs labour). I'm tempted to give the car to him instead of the BMW guys because there's a £200 saving BUT the caveat is that he's not a specialist and in the past he couldn't even fit BMW Upper spring pads because they were too tight. Fingers crossed he'll have no issues with the RSFB!!

[bmw_solid]

Originally Posted by Tambohamilton

It seems like you want to put stock bushings back in there... Best get on with it! Anything will be better than aged, cracked rubber!

Yes I have made up my mind now. Its got to be the Stock Lemforder RSFB. I am fearful of what solid rubber can do the these cars. Just using the Monroe upper rear shock mounts caused me grief for 1 week which i'll never forgot so I can't risk it again with these M3 rubbers. The E9x chassis is under-dampened by nature for extra road feel and driver-focus and I don't mind that but I can't take the risk of worsening it - that's when these cars become unpleasant.

The worst part is this: On the forums, people have polarizing views of mods. Upper Monroe mounts, Poly subframe bushings: You'll get people praising them and you'll get people cursing them! So I'd rather sacrifice on sharp handling and settle for 'good' handling with no effect on comfort.

If I do go ahead on replacing the bushings (just need to make sure my mechanic is confident for the job), then I'll definitely give my feedback here. Stock RSFB is not documented on these forums.