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Thread: RTAB theory and questions

  1. #1
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    RTAB theory and questions

    Okay, the standard RTAB's on e36's and e46's are rubber, obviously, and I, personally, have been using the stiffest OEM ones (euro 3.2 e36) I could find with the Turner limiters (on my e36 M3 and my DD e46 ZHP).
    However, on my wife's e46 M3 we've got a set of TC's spherical RTAB(earings).. And we have been using them for street and track.. They were part of the package deal and the car is used about 50/50 street and track.
    I don't like the idea of the bearings on that car in that location on the street since it's loud, obviously.
    The question I have is related to the Delrin or Poly RTAB's. That is a multi-axis movement in that location, so I can't wrap my head around anything except for rubber with limiters, or bearings. However, plenty of reputable shops and/or people are selling poly and Delrin for that loaction.
    In my mind that would transfer significantly more stress to the cup in the chassis where that is mounted and that is known to fail on many cars... Not a good option really, right? I guess that could be reinforced, but still...
    What thoughts or actual real world results have been acheived by these parts?
    Another thing I would think about is the poly parts actually tearing as poly can tend to do under compression. Has anyone seen this on track or street?
    Additionally, I'm thinking about keeping any mods on the e36 legal for a prepared class car, so that's my thought on that one.
    Are the only real options rubber with limiters or bearings... Or are the Poly/Delrin Parts fully reliable (as much as the rubber/spherical otpions anyway)?
    What do you all think?

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    Quote Originally Posted by mtrsprt View Post
    What do you all think?
    I think that you are exactly correct.

    There are several prepared class options available to you.

    Jay

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    Oh yes, many options, but I can't wrap my head around the idea of running Delrin or Poly at this point, due to the fact that it is a multi-axis movement through the range of the suspension travel.
    Any thoughts on that theory?
    Or on the actual strength and "long term" reliability in actual track use of the poly bushings or delrin or the cup in the chassis where that is located?

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    I ran delrin bushings for close to a year when the car was doing dual duty. I never had any issues with any cracking or breaking of parts.

    That being said... I now have OE rubber bushings and BMS limiters (IP car) and the rear end feels better than it did with the delrin. It's hard to explain, aside from it just feeling more "proper."


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    Quote Originally Posted by mtrsprt View Post
    Okay, the standard RTAB's on e36's and e46's are rubber, obviously, and I, personally, have been using the stiffest OEM ones (euro 3.2 e36) I could find with the Turner limiters (on my e36 M3 and my DD e46 ZHP).
    However, on my wife's e46 M3 we've got a set of TC's spherical RTAB(earings).. And we have been using them for street and track.. They were part of the package deal and the car is used about 50/50 street and track.
    I don't like the idea of the bearings on that car in that location on the street since it's loud, obviously.
    The question I have is related to the Delrin or Poly RTAB's. That is a multi-axis movement in that location, so I can't wrap my head around anything except for rubber with limiters, or bearings. However, plenty of reputable shops and/or people are selling poly and Delrin for that loaction.
    In my mind that would transfer significantly more stress to the cup in the chassis where that is mounted and that is known to fail on many cars... Not a good option really, right? I guess that could be reinforced, but still...
    What thoughts or actual real world results have been acheived by these parts?
    Another thing I would think about is the poly parts actually tearing as poly can tend to do under compression. Has anyone seen this on track or street?
    Additionally, I'm thinking about keeping any mods on the e36 legal for a prepared class car, so that's my thought on that one.
    Are the only real options rubber with limiters or bearings... Or are the Poly/Delrin Parts fully reliable (as much as the rubber/spherical otpions anyway)?
    What do you all think?
    Yes you are mostly correct except I would like to ask one thing. What part number were you using for the OEM rubber RTAB that you say are the stiffest from a Euro M3?

    Do you know about the updated design from BMW itself with part number
    33-32-6-770-817?

    These RTAB's with this part number are an updated design from BMW itself. This are the stiffest and most stable rubber bushings you can buy. I would highly recommend installing these bushings. I have installed them twice on my cars and don't have to worry about noises/squeaks or any added stress to the subframe.

    http://www.pelicanparts.com/bmw/cata...SUSshk_pg5.htm
    http://www.rmeuropean.com/BMW-Ball-J...3326770817.htm

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    yup, this is the very reason I went with new rubber bushings and limiters on a pretty agressive suspension


    Quote Originally Posted by dallasfan824
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    Im running delrin rtabs on my track/street E36. No problems at all, except for the noise.

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    Quote Originally Posted by qidm67 View Post
    Yes you are mostly correct except I would like to ask one thing. What part number were you using for the OEM rubber RTAB that you say are the stiffest from a Euro M3?

    Do you know about the updated design from BMW itself with part number
    33-32-6-770-817?

    These RTAB's with this part number are an updated design from BMW itself. This are the stiffest and most stable rubber bushings you can buy. I would highly recommend installing these bushings. I have installed them twice on my cars and don't have to worry about noises/squeaks or any added stress to the subframe.

    http://www.pelicanparts.com/bmw/cata...SUSshk_pg5.htm
    http://www.rmeuropean.com/BMW-Ball-J...3326770817.htm
    If it makes any difference to you, I don't like the new ones. I have seen them move laterally, and they dont seem any stiffer than the 33-32-2-228-153 if I pry with a screwdriver.

    Thats all. two cents worth, but I certainly wouldn't pull out fresh old part numbers to put in fresh new part numbers.

    I am inclined to actually go the other way on my own car.

    Jay
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    Quote Originally Posted by Hellabad View Post
    If it makes any difference to you, I don't like the new ones. I have seen them move laterally, and they dont seem any stiffer than the 33-32-2-228-153 if I pry with a screwdriver.

    Thats all. two cents worth, but I certainly wouldn't pull out fresh old part numbers to put in fresh new part numbers.

    I am inclined to actually go the other way on my own car.

    Jay
    When you pryed them a screwdriver where they installed on the car or not? I ask because they compress when installed.

    Also the old part number with 153 will still move laterally with screwdriver.

    You have to understand when installed onto the console and bolted to the chassis the geometry changes.

    You guys see that HPF E46 M3 1000HP on the dyno where the RTAB's are moving?

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    Quote Originally Posted by qidm67 View Post
    You have to understand when installed onto the console and bolted to the chassis the geometry changes.
    I'm going to go out on a limb here and guess that Jay understands any geometry changes going on with suspension parts.


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    Quote Originally Posted by JonathanL View Post
    I'm going to go out on a limb here and guess that Jay understands any geometry changes going on with suspension parts.
    I would agree but we await for his answer

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    Quote Originally Posted by mtrsprt View Post
    Another thing I would think about is the poly parts actually tearing as poly can tend to do under compression. Has anyone seen this on track or street?
    What do you all think?
    I replaced a set of Polyflex urethane RTABs on a customer's car that had about 100k miles on them. We replaced them with new Polyflex units, but even the old ones we pulled out didn't look very bad at all. No cracking.

    Erik

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    Delrin RTABs are awful with street duty. I'm never going there again. Powerflex works because it's soft enough to allow a little movement.
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    Quote Originally Posted by mtrsprt View Post
    The question I have is related to the Delrin or Poly RTAB's. That is a multi-axis movement in that location, so I can't wrap my head around anything except for rubber with limiters, or bearings.
    Don't conflate Delrin and Polyurethane. Delrin is extremely rigid, comparable to a weak metal such as brass. Unless the Delrin is made as a bearing it has essentially no multi-axis movement. By contrast Polyurethane, at least in the grades used for automotive aftermarket bushings, is almost three orders of magnitude more elastic. Poly RTAB bushings certainly offer multi-axis freedom of motion, albeit with more resistance than rubber except around the mounting axis.

    Experience suggests that poly RTAB bushings work fine. They're also easy to replace if necessary, since they're not pressed in.

    The thing that would worry me for RTAB applications is shock loading. Rubber or poly both cushion shock loads, spherical or Delrin bearings, meh, not so much. I wouldn't use those without major reinforcement of the RTAB carrier mounting area.

    Neil

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    Quote Originally Posted by NeilM View Post
    Don't conflate Delrin and Polyurethane. Delrin is extremely rigid, comparable to a weak metal such as brass. Unless the Delrin is made as a bearing it has essentially no multi-axis movement. By contrast Polyurethane, at least in the grades used for automotive aftermarket bushings, is almost three orders of magnitude more elastic. Poly RTAB bushings certainly offer multi-axis freedom of motion, albeit with more resistance than rubber except around the mounting axis.

    Experience suggests that poly RTAB bushings work fine. They're also easy to replace if necessary, since they're not pressed in.

    The thing that would worry me for RTAB applications is shock loading. Rubber or poly both cushion shock loads, spherical or Delrin bearings, meh, not so much. I wouldn't use those without major reinforcement of the RTAB carrier mounting area.

    Neil
    The other problem is that the 3 mounting bolts can literally tear out of their holes with delrin... not much you can do to reinforce that.


    Quote Originally Posted by dallasfan824
    TC does not want ghey hookers you silly.

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    Quote Originally Posted by TC535i View Post
    The other problem is that the 3 mounting bolts can literally tear out of their holes with delrin... not much you can do to reinforce that.
    Yeah that's what happens, I have seen personally three times and a few times on this forum. This happens with polyurethane bushings and it's not worth the risk. Some of the M3's are reinforced around that area and some aren't from the factory, I think they use MIG welds around it otherwise spot welds.

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    The other problem is that the 3 mounting bolts can literally tear out of their holes with delrin... not much you can do to reinforce that.
    Sure you can...

    http://store.bimmerworld.com/Product984

    Yeah that's what happens, I have seen personally three times and a few times on this forum. This happens with polyurethane bushings and it's not worth the risk. Some of the M3's are reinforced around that area and some aren't from the factory, I think they use MIG welds around it otherwise spot welds.
    Quit spreading BS. This happens with RUBBER bushings too. The material we use is much firmer than factory rubber but nowhere near the hardness of your 'solid' materials. There is ZERO reinforcement here from the factory on any E36. The nutserts your bracket bolts into are not flush with the body, this allows the bracket to flex on top of them. Eventually they crack and fall out do to this movement.

    Rubber = Super Soft.
    Poly = Soft.
    Delrin = Solid.
    Last edited by robweenerpi; 07-31-2008 at 04:44 PM.

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    I've been running Powerflex polyurethane RTAB's for 2 years in a daily driven E46 with no issues of sound or signs of stress on the mounts.

    For sure, I think it needs to be clarified that delrin and polyurethane are very different, physically. Polyurethane has some "give" while delrin is solid almost like ABS plastic or nylon (probably a bad analogy).

    For your wife's E46 M3, consider between Powerflex RTAB's or OEM rubber and limiters. I chose the give Powerflex a try because of the easier/simpler install.

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    True, Delrin is much, much harder than the rubber or the Poly... Basically solid, like UHMW, Nylon, etc... Of course, the Poly mounts' hardness is determined by the durometer of the polyurethane... We use alot of Delrin, Poly, and other hard plastics in my "day job"... Our polyurethane is 60, 70, 80, or 90 durometer for the most part.
    Speaking of that, what are the durometers of the Powerflex and/or UUC bushings? Or even the various rubber ones, since I never tested any of those here.
    I will be taking the bearings out of the e46 M3 and shelving them until they are used in a mod race car some day...
    The Delrin is certainly out since it's too rigid and, in my opinion, transfers too much rotational stress to the mounting point in the chassis... Not worth it for any of the cars listed here. And, to be honest, I don't personally feel it's a great idea for that location.
    So, rubber or poly it is...
    Poly would probably be nice, but the rubber with limiters is good... Decisions, decisions.
    Without the "shock" problem with the bearings, they do seem like the best solution for that location, since all of the others are being twisted, pulled, or pushed somwhat... They are kind of annoying on the street, though... Perfect for a dedicated track toy where they are legal for use.

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    I'm not sure what the durometer is for the Powerflex polyurethane RTAB's.

    Here's what they look like, from what I found in this thread:
    http://forums.bimmerforums.com/forum...d.php?t=489630


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    I ordered a set of PF's today. They seem to have a reputation for not squeeking and adding little or no NVH. My stock ones don't seem that bad to me, but we'll see how wrong I am soon. I'll report back next week after I get the work done.

    Chris

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    Quote Originally Posted by mtrsprt View Post
    Okay, the standard RTAB's on e36's and e46's are rubber, obviously, and I, personally, have been using the stiffest OEM ones (euro 3.2 e36) I could find with the Turner limiters (on my e36 M3 and my DD e46 ZHP).

    The question I have is related to the Delrin or Poly RTAB's. That is a multi-axis movement in that location, so I can't wrap my head around anything except for rubber with limiters, or bearings. However, plenty of reputable shops and/or people are selling poly and Delrin for that loaction.
    In my mind that would transfer significantly more stress to the cup in the chassis where that is mounted and that is known to fail on many cars... Not a good option really, right? I guess that could be reinforced, but still...
    What thoughts or actual real world results have been acheived by these parts?

    Another thing I would think about is the poly parts actually tearing as poly can tend to do under compression. Has anyone seen this on track or street?
    Additionally, I'm thinking about keeping any mods on the e36 legal for a prepared class car, so that's my thought on that one.

    Are the only real options rubber with limiters or bearings... Or are the Poly/Delrin Parts fully reliable (as much as the rubber/spherical otpions anyway)?

    What do you all think?
    Well its good to see people like yourself actually thinking about these issues. And you are right in your thinking - polyurethane is usually a bad choice for a bushing material if it has to deflect - such as in a multi-axis suspension bushing location. Rubber bushings + limiters or Sphericals are the only two textbook choices for an RTAB. I cannot count the number of times I've seen RTAB or LCA failures on BMWs. At the very least they do add bind during significant suspension movement... and yes, stress to the chassis at their mounts.

    That said, many road racers have had good results with poly in these 2 locations (meaning: no failures and less deflection vs. the OEM rubber). This is probably due to the higher spring rates and smoothness of tracks they tend to run with - higher spring rates and smooth tracks limit suspension travel and thus bind at these bushing locations. So there's gonna be hundreds of racers that say "use them, they work". And they do - in those situations. If you have a street car or dual purpose BMW your results might not be so positive.

    edit: oh yea, polyurethane does come in many durometers, and some of it has some notable compliance. Shoreline A 85-95+ stuff is pretty darn stiff, but 70 and down can be fairly pliable.

    Cheers,
    Terry Fair @ Vorshlag Motorsports

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    I've said it before and I'll say it again:

    The performance improvement of non-OE RTAB bushings is negligible over the factory bushings..... so why run them????

    They're noisy, harsh, and increase energy transfer. Bad, bad, and bad.

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    Quote Originally Posted by Eric98Sedan View Post
    The performance improvement of non-OE RTAB bushings is negligible over the factory bushings..... so why run them????
    Is this with or without the RTAB limiters used with OE bushings? When I was running new OE bushings without the limiters, I would get enough toe change that my tire would rub the inside of the wheelwell. I don't get this rubbing when I use limiters.

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    Quote Originally Posted by 4ZPN View Post
    Is this with or without the RTAB limiters used with OE bushings? When I was running new OE bushings without the limiters, I would get enough toe change that my tire would rub the inside of the wheelwell. I don't get this rubbing when I use limiters.
    Toe change when, exactly?

    I've never run the limiters because they diametrically oppose the design of the suspension, so in my mind, they can't possbily 'improve' perfromance. At most, they will introduce some degree of bind/resistance as the suspension compresses and yes, I suppose, limit toe change during extreme acceleration and/or braking. But I don't rub at all with a 1.5ish rear drop, super soft springs (400) and factory 8.5" LTWs.

    But as I said, I've yet to run them so what do I know.
    Last edited by Eric98Sedan; 08-01-2008 at 10:35 PM.

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