RTAB replacement...
- Thread starter Ducklakeview
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I fitted powerflex to a Honda S2000 and an Mx5, on the Honda the front bushes were fine but I had to machine the rears, on the MX5 all the bushes had to be skimmed as when the bolts were tightened up you couldn't move the wishbones, I set them with a 5 thou clearance and lube them but to be honest back to back I saw no difference between brand new rubber and Powerflex on the MX5, the S2000 was a high mileage car so the poly bushes helped but I'm not convinced they are any benefit at all on the road over a new rubber bush!
Fitting solid bushes on a track car is ok as long as the pick up points line up correctly, you would be surprised how liberal the tolerances are on some cars, the beauty of spherical joints is they self align so you get zero binding or installation issues, not for the road though!
Fitting solid bushes on a track car is ok as long as the pick up points line up correctly, you would be surprised how liberal the tolerances are on some cars, the beauty of spherical joints is they self align so you get zero binding or installation issues, not for the road though!
Ok, but that is on other cars. I dont see how that has anything to do with the z4 of rtab's.Artful-Bodger said:
I have a video here on the forum that prooves that none of this is the case on the z4. It all moves fine.
As for improvements or not, especially the rtab's are soft and change wheel alignment under bounce/stress or breaking.
In theory all compliant bushings do that. Whether thats a good thing or not one can decide for themselves. But for example the z4m has a ball joint on the lower outer lateral arm where the normal z4 has a compliant bushing. Somewhere they thought that was an improvement I guess (or at least shifting the trade off from comfort to performance), and a simple one at that as they already had the part.
No, the spring gives support between chassis and arms. the shock limits the bounce, what is the contact patch leaving the road. Without shocks your wheels are off the road half the time bouncing in the air.Ewazix said:
And as I said, when the suspension arms deform (or better said, bushings get compressed) wheel geometry changes and that changes the desired wheel geometry set by the suspension arm settings, reducing that tyre contact patch what can result in less grip, tyre wear or reduced agility etc. Thats why racecars have solid joints in the suspension. Way to harsh for the road (and probably for the chassis without reinforcements) but ideal if you want to have maximum grip and handling. If that wasnt the case, an F1 car would be full of soft rubber bushings (money is no object) but instead its all ball joints.
GuidoK said:
Not sure where your seeing a ball joint in the rear M suspension? which model do you refer to?
Here is good advice on the fitment of uprated bushes for the M onto the Z4 - http://www.vorshlag.com/product_info.php?cPath=1_4_26&products_id=515, you may note they mention the issues with using polyurethane, this does merit some further investigation, there is a fair bit of information on the subject.
I have fitted poly bushes on a couple of cars for competition work with road tyres and the results are the same, if your replacing worn rubber with new poly you will see an improvement, just as you will if you replace worn rubber with new, but what was of interest was the Mx5 in question had new rubber bushes fitted, my friend who owned the car then decided if new rubber made such a difference poly was going to improve it again, so two weeks after fitting new rubber , out they came and in went the Powerflex, after much fiddling to get them working the result was for all the effort, bugger all difference to new rubber!
It really comes down to what rubber and what poly, hard rubber bushes are expensive, whilst poly is a cheap alternative, if the rubber is fitted correctly it works fine, half the time rubber is destroyed by not setting it correctly on installation, you have to put the car back on it's wheels and roll it back and fore to settle the suspension before tightening, most people and garages don't.
For the track I ended up using Delrin on the Westfield, just like aluminium it sucks on the road but works great on the track providing the suspension works in a non conflicting arc, on the Z4 rear for instance you can easily see the way the upper and lower lateral arms attached to the upright work in one arc at 90 degrees to the lower fore/aft arm, just drawing this you can see the two arcs conflict and this is where the rubbers compliance becomes important, otherwise your pulling and twisting components in a conflicting movement, for the track I would replace all the bushes with spherical bearings as they then work in one axis like a large wishbone.
It's up to the individual but I would not use poly bushes on a road car, especially if there are uprated hard rubber bushes available as there seems to be for the M models.
Have gone for MEYLEHD and those cheap limiters, now that I know how to fit them properly.
Mike
Mike
I will be changing the bushes on my Z4 this winter when the cars off the road, I am interested in the Meyle HD offerings but am also looking at the Z4M components to see what's available.
For the front, Meyle arms will replace the current ones but I want to have a look at the Z4M eccentric rear bushes before I order, These are of interest as they add more castor which will affect the camber control under steering lock, but as usual there is the consideration of how much load that will apply to the top strut mounts, it may require Z4M top mounts or some modification or ball mount to realign everything, measurement will tell.
I will also take the opportunity to modify the front A/R bar so I can adjust it and source a smaller bar (mine is M sport) and modify that too so I can swap them around.
Not had this Z4 long but even with an initial inspection I can see many areas which can be improved over standard, I will get everything measured up over the winter, calculate some new spring rates and start doing some chassis development.
For the front, Meyle arms will replace the current ones but I want to have a look at the Z4M eccentric rear bushes before I order, These are of interest as they add more castor which will affect the camber control under steering lock, but as usual there is the consideration of how much load that will apply to the top strut mounts, it may require Z4M top mounts or some modification or ball mount to realign everything, measurement will tell.
I will also take the opportunity to modify the front A/R bar so I can adjust it and source a smaller bar (mine is M sport) and modify that too so I can swap them around.
Not had this Z4 long but even with an initial inspection I can see many areas which can be improved over standard, I will get everything measured up over the winter, calculate some new spring rates and start doing some chassis development.
Artful-Bodger said:
These: https://www.turnermotorsport.com/p-...ailing-arm-bushing-limiter-kit-rtab-shim-kit/
But I went for a cheaper set, which should be here shortly (only ordered yesterday) ; http://www.ebay.co.uk/itm/172293352605?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Fitting in conjunction with MeyleHD bushes; http://www.ebay.co.uk/itm/321731382470?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Mike
33326775551Artful-Bodger said:
They are trying to sell their own product....... so they write this piece with a commercial interest.
Just as in that other discussion someone also blindly believed what commercial websites had to say that would fit right into their offered product line....
They also say for instance "Polyurethane can and will cause suspension bind." which is 100% NOT true if you dont go over shore95A. That shows how badly that piece is written and how much they want to sell their own product. Only a fool falls for that. In that other topic I posted a video to prove that (as my hands on experience wasnt believed...)
And I have actually fitted it on a z4, and my previous bushings werent worn.
And also then its an improvement. There was no such thing as slack or seizing up as you speculated. (as seen in that video I made)
I swapped all my bushings on the rear axle in little over 3 hours once I had the rear axle out. Yes, that is all 19! bushings in 3 hours (well 15 bushings and 4 ball joints to be exact). Getting the poly bushings in is much much easier and faster than oem rubber ones.
So I dont know where the much fiddling part has to come in, maybe its a personal thing. I had none of that. It was a matter of putting them in, lubricating and go. simple as that and they have been there for years now, on a rear axle that gets about 66% more power than stock.
So everything you seem to have experienced on other cars hasnt been happening on my install on the z4 it seems.
I'm sorry to say so but this informantion is also incorrect. The z4m uses exactly the same bushings as the normal z4 does. So rtabs and both inner lateral arm bushings are EXACTLY the same. If you think otherwise...you're misinformed. The only difference -as I already wrote- is that it uses the upper outer lateral ball joint also on the lower outer lateral joint. And thats an easy upgrade. There are also poly bushings for this point but you can just as well fit that balljoint. I believe its even cheaper too if you dont get it at the stealers.
Meyle HD has a bushing that is supposed to last longer, its not made to be significantly stiffer. HD stands for high durability.
So that will still have lateral movement (without limiters that is) and longitudal movement (limiter rings dont do anything about that)
GuidoK said:
Ducklakeview said:
Ahh nice one, thanks for that.
I can turn up a set, I have some 75mm Delrin bar here that should suffice, has anyone tested these for angular clearance with wheel travel?
Artful-Bodger said:
I think polyurethane is more expensive than synthetic rubber and is more difficult to make in automated series processes.
But how can you disagree with the bind argument?!? I have Video proof!
I mean how clearly do you want to have it put down? You think I faked the video?!?
There is no binding or seizing. It all moves freely. I dont see how you can disagree with proof on video.
Can I ask you another question? Where's your proof? where is your actual proof to back up your claims? I've only seen speculations.
Also polyurethane is known to last a fair bit longer. the fcarbs are prone to wear very quickly and those have been tested for ages. Mine have been on the car for 6 years and still feel like new. And that is longer than the factory ones were on there and they failed.
Well mine are also torqued at factory spec, and it moves fine and freely as seen in the video. And it was an easy install. I dont know what else to make of it. It was no big deal.
I dont know where your install went wrong other than that it wasnt on a z4 so I also dont know what it has to do with this discussion.
Apparently your experiences or abilities are different than mine.
The rtab bushings are the same partnumber for the z4m and the normal z4's. The same product. Just look it up in the ETK.
You were probably misguided from some e46 site.
This info is really easy to acquire.
The only argument against polyurethane bushings I can come up with is that you loose some comfort in exchange for better handling, choice of stiffness and in some cases longer life (and with easy install if you stick to the quality products and dont cheap out).
But you also loose comfort with harder normal rubber or limiter rings as those also limit complient movement. But thats the whole idea.
Poly can be turned out on CNC very cheaply, but still can you give an example of Polyurethane being used by manufacturers, I'm sure there must be someone if it's so superior in service life, an issue I do not contest by the way.
I note on your video when your suspension is moved you can hear the creaking, polyurethane is quite a sticky material and this grabbing is one of the issues I work to eliminate, I install the bushes then test the movement of the items individually, the installation is correct (for my requirements) when I get free movement with no sticking, I found 5 thou and properly lubed eliminates this with no side play, only then do I assemble the suspension and check it again, and it's then that you find how much the tolerances and deflections come into play, we obviously have different requirements!
The bush numbers are the same for the E86, I speculate the E85 (my car) has had it's part superseded by the later version?
Now what has me curious is why they are only making a ball joint for the top arm?, all lower arms bushes seem to be rubber, this points to a loading issue at the top, I would need to measure up and compare upper and lower joints but I fail to see a sound reason why a ball joint is not specified for the lower arm?
The inner bushes should take care of NVH, so maybe I need to design a lower ball joint and dust seal?
I note on your video when your suspension is moved you can hear the creaking, polyurethane is quite a sticky material and this grabbing is one of the issues I work to eliminate, I install the bushes then test the movement of the items individually, the installation is correct (for my requirements) when I get free movement with no sticking, I found 5 thou and properly lubed eliminates this with no side play, only then do I assemble the suspension and check it again, and it's then that you find how much the tolerances and deflections come into play, we obviously have different requirements!
The bush numbers are the same for the E86, I speculate the E85 (my car) has had it's part superseded by the later version?
Now what has me curious is why they are only making a ball joint for the top arm?, all lower arms bushes seem to be rubber, this points to a loading issue at the top, I would need to measure up and compare upper and lower joints but I fail to see a sound reason why a ball joint is not specified for the lower arm?
The inner bushes should take care of NVH, so maybe I need to design a lower ball joint and dust seal?
Making something cnc is way way more expensive than the stamping and molding the normal vulcanized bushings undergo.Artful-Bodger said:
CNC is only used in series production if you absolutely have to. So it's definately a cost issue.
First you try to stamp, if thats not possible you try to cast and if thats not possible you do machining. thats the flow from cheap to expensive.
The poly bushings are I think partly cast and partly machined. I dont think you can get the knurled surface just by casting. Cheaper ones dont have that knurling as I pointed out in the beginning of this topic with that psb bushing
So poly bushings are difficult to manufacture in numbers that normal bushings are. I think there's quite a bit of manual labour involved. I've seen pictures of the powerflex factory (and thats one of the biggest manufacturers) where they had hand molds and everything, so labour intensive. (that was before it burned down, I dont know how it is now but I imagine the process is still the same)
You cant hear that while driving or when pushing wobbeling the car up&down when it sits on its wheels and the suspension is force loaded. So the ride is quiet.
I know what you mean (as I hear it too) but I dont know if that even comes from the bushings. but there is no bind or anything of that. it moves freely under its own weight, let alone under hundreds/thousands of pounds of spring/suspension pressure so that cant be an issue like you speculated.
BTW suspension with oem rubber bushings can also creak pretty loudly. I have a 5 or 6 year old bumpercam vid somewhere (from before I started polybushing the car) where you can hear the front suspension creaking when I drive through town over the speedbumps. dont know if that are the arb bushings or fcab's. You couldnt hear it at the time in the interior but that dashcam picked up a lot more.
Just look in the etk and it all comes clear, like I said, this info is really easy to find. especially with all that experience.
I'm sure you'll figure it out like I did years ago.
I'm pretty sure if poly was a superior material you would find manufacturers utilising it in their products as it's service life is longer than rubber so I'm not convinced just cost is the real issue, especially as NVH is such an important development consideration!
The creaking is the poly grabbing, it leads to the annoying squeak you get on some cars, at rest and at room temperature you can hear and feel it, it becomes a problem when your car is moving as the bushes sticking heats them up expanding them and causing more grabbing, I know this from my own problems trying to eliminate it on my Westfield years ago, do a run round the track, disconnect the coilover and anti roll bar and see how stiff it's getting, I resolved the issue by going to Delrin initially and later spherical joints on the Westfield.
You wouldn't accept your dampers sticking and making sure your suspension moves correctly with no resistance is well worth the effort when your tuning dampers and pressures!
Your obviously convinced by poly for a road car, I am not, it's as simple as that, so no worries if that's your choice, but poly is not an ideal material and you can't tell people they are wrong when their experiences do not match yours, you can simply state your own experiences!
The RTAB I have here is obviously an earlier one I purchased from the local dealer for measurement, it differs in the slot gap to the later ones on the net so that's probably the confusion over the parts, if the later part has a higher compression installation (easy to check the od) then that's my first choice, thanks for the heads up on the top balljoint as mine has rubber at present!
Front bushes are on the list for enquiry too, Z4M being of interest, does anyone have any experience of these?
The creaking is the poly grabbing, it leads to the annoying squeak you get on some cars, at rest and at room temperature you can hear and feel it, it becomes a problem when your car is moving as the bushes sticking heats them up expanding them and causing more grabbing, I know this from my own problems trying to eliminate it on my Westfield years ago, do a run round the track, disconnect the coilover and anti roll bar and see how stiff it's getting, I resolved the issue by going to Delrin initially and later spherical joints on the Westfield.
You wouldn't accept your dampers sticking and making sure your suspension moves correctly with no resistance is well worth the effort when your tuning dampers and pressures!
Your obviously convinced by poly for a road car, I am not, it's as simple as that, so no worries if that's your choice, but poly is not an ideal material and you can't tell people they are wrong when their experiences do not match yours, you can simply state your own experiences!
The RTAB I have here is obviously an earlier one I purchased from the local dealer for measurement, it differs in the slot gap to the later ones on the net so that's probably the confusion over the parts, if the later part has a higher compression installation (easy to check the od) then that's my first choice, thanks for the heads up on the top balljoint as mine has rubber at present!
Front bushes are on the list for enquiry too, Z4M being of interest, does anyone have any experience of these?
Artful-Bodger said:
Well you did make claims about seizing/binding that you couldn't proove. I asked for proof and nothing came up....oddly. All you do is refer to other cars, but this is a z4 specific discussion. I'm showing you a video that you can freely move the suspension by hand.
How much resistance will an clamped in OEM rubber bushing give?
A lot more. And then you talke about the resistance the poly bushing has interfering with the precision tuning of the shock? So that rubber oem bushings compliance miraculously goes away? Moving the oem rubber suspension in that shock travel will require more force as you have to stretch all that rubber.
Plus what you say here; right back at you. I cant tell people they are wrong and you can? How does that work?
As for the superior material argument: do you really think manufacturers go for the best material?
It might be an eye opener, but they go with the cheapest material they can get away with. Clearly for a bushing that is simpel rubber and zinc plated steel press fit. Cheap materials and easily mass produced.
As long as it doesnt break in the first 5 years or so they're safe. After that the original customer most likely has moved on to a newer model and warranty is over. The only thing they really want to avoid is recalls as they cost a lot of money.
Every dime they can save in the price of the new car gives more ensurance that customer will come back for the next model.
If you buy a powerflex bushing you get lifetime guarantee.... thats pretty good for a crappy product not? I dont see that happening on any OEM product.
Jeez, what a can of worms, I only asked a simple question! 
Mike
Mike
99% of mass produced Polyurethane bushes aren't machined, they are two-pack reaction (RIM) or pellet material cast and so are as cheap as chips, particularly compared to the dual density or oil filled bushes found elsewhere on the BMW suspensions. So I can't see cost being the defining reason why Poly doesn't seem to be factory fitted, even by some notably expensive high performance makers.
Lack of NVH suppression, transmission of damaging forces over the longer term life of a road car and the famous poly squeak (fully acknowledged by poly engineers and makers - hence the regular lube recommendations) are probably why they are not an OEM fit.
Lack of NVH suppression, transmission of damaging forces over the longer term life of a road car and the famous poly squeak (fully acknowledged by poly engineers and makers - hence the regular lube recommendations) are probably why they are not an OEM fit.
OEM rubber style bushings are easily mass produced and hence much cheaper. thats why almost all car manufacturers use them.
Some race classes allow polyurethane bushings. the mini challenge cars are fit wih polyurethane bushings. Clearly due to their superior performance over the stock OEM bushings
It's well known that poly bushings dont age like normal rubber bushings and thus have a longer life expectancy. Take for instance the fcab's on the z4, a well known failure point where poly bushing last much longer. No wonder they can come with a lifetime guarantee. OEM manufacturers wouldnt be able to keep up with the claims. I think bmw's longest warranty period is 5 years if you pay extra for it.
Some race classes allow polyurethane bushings. the mini challenge cars are fit wih polyurethane bushings. Clearly due to their superior performance over the stock OEM bushings
It's well known that poly bushings dont age like normal rubber bushings and thus have a longer life expectancy. Take for instance the fcab's on the z4, a well known failure point where poly bushing last much longer. No wonder they can come with a lifetime guarantee. OEM manufacturers wouldnt be able to keep up with the claims. I think bmw's longest warranty period is 5 years if you pay extra for it.
Yes for race cars, I have used them myself, I also stated I do not consider them worthwhile on a road car many times!
I also left them behind on my race cars as there were better options, but this thread is about road cars.
I also left them behind on my race cars as there were better options, but this thread is about road cars.
So if it acts like a spring it still interferes with the dampening of your car. Affecting the spring characteristic of the main spring.
the polybushed suspension drops under its own weight, so if there is any resistance, its negleable. Less of an effect to the main spring and shock.
Thus better
, apart from that the oem bushings flex all over the way, disturbing wheel geometry on all of its joints. The popular limiters only limit movement on 1 bushing in 1 direction. Its a start but just the tip of the iceberg.
Fully polybushed the rear suspension feels so much more planted and predictable than stock.
the polybushed suspension drops under its own weight, so if there is any resistance, its negleable. Less of an effect to the main spring and shock.
Thus better
, apart from that the oem bushings flex all over the way, disturbing wheel geometry on all of its joints. The popular limiters only limit movement on 1 bushing in 1 direction. Its a start but just the tip of the iceberg.Fully polybushed the rear suspension feels so much more planted and predictable than stock.
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