# Why (Rear) Poly Bushings Are Bad



## Ceilidh (Jan 7, 2004)

Hi Everybody!
I was doing a little web research for Peter/Pyce (he's doing some neat rear suspension Solidworks modeling -- look out for it over the next few days), and came across a really nice Forum explanation for why poly bushings can be troublesome in the rear suspension. Since some of you seem to be interested in the topic, I thought I'd repost it for you all to read. (Please note that I'm just reposting someone else's thoughts, and don't feel strongly about this issue myself!)








Anyway, we'll do it in parts. Halfway through the discussion was this observation from a Virginian named sccaITA16V:

_Quote »_ 
Bills comments are right on, and I would like to share my personal experience with bushings.
On my race car I originally used delrin front and rear for the first two seasons, then switched to Mr. Shines bearings. The first thing I noticed was that when I jacked up the car, the suspension immediately fell to full droop, whereas with the delrin setup the suspension in the front would s l o w l y fall and in the rear not drop at all! Obviously the delrin was binding.
On the street, I have seen friends with poly in there LCA and after a few years experience "slop" in the suspension. Upon tear down we discovered the control arm was pivoting around the poly bushing, which allowed the paint to scrape away and rust, and this cycle continued till it loosened up the tolerances so much you could feel slop in the suspention!
just my two cents 


....followed by this comment from Vortex regular (and New Englander!!) bobqzzi:

_Quote »_
By their very nature and design polyurethane control arm bushing cannot function properly. In a normal rubber bushing the steel center sleeve is locked in place and the rubber a tight press fit on the OD. As the arm moves up and down the rubber twists radially. All the motion is in the rubber shearing, not the most precise system, but it works quite well for street cars, and the rubber lasts a good long time. The downside is sideways deflection under cornering loads.
A polyurethane bushing works in a different manner altogether. The center steel sleeve is still locked in place, so it doesn't move. The OD is allegedly fit tight enough so the poly material doesn't move either. So all the up and down motion causes the poly to rotate around the steel sleeve. So in effect the sleeve is a bearing and the poly outer is the race. Given the physical characteristics of poly, and the realities of making it press fit into the control arm, yet still have a perfectly round hole to act as a bearing race, there are two conditions that are usually achieved.
When first installed the sleeve fits very tightly in the poly outer, which prevents lateral deflection under cornering. However, it also binds the arm so badly that it is virtually impossible to move it up and down, this is called stiction, and results in odd, undesirable handling characteristics. This can be somewhat alleviated with a special lube.
After being installed for a while the sleeves typically machine a larger hole..someplace in this process is a "sweet spot" where they actually work okay for a little while. However, as they continue to work, and pick up all sort of lovely "grinding paste" from the outside environment the holes continue to get larger, usually taking on an oblong shape. This, of course, results in a load of lateral deflection when cornering. At some point the outer poly gets loose enough that it starts moving around in the arm itself. After a while this begins to enlarge the hole in the arm-not good.
It is a very, very silly design, and I've removed dozens of sets that have done just what I've described.
As I see it, the alternatives are stock bushings, hard rubber bushings (I don't know if any are currently made, VW motorsport used to have them), or the Shine Racing kit which puts teflon lined spherical bearings in place of the bushings. They actually ride better than poly bushing, although they do transmit more road noise than stock rubber ones. They also last virtually forever.



And, for those of you who'd like to see the discussion in its original context, here's the link:
http://forums.speedarena.com/z...27049
Once again, yours truly has no views on this subject (I can tell you why I hate nylatron/delrin/poly bushings on a 1974 MGB vintage racer, but that experience so scarred me that I've never tried anything like that on any car ever since -- hence I don't know what they're like on a VW!) -- here, I'm just a reposter!








Cheers everyone,
-C


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## groftja (Jul 19, 2004)

*Re: Why (Rear) Poly Bushings Are Bad (Ceilidh)*

Ceilidh for president!








I have a question about hard rubber bushings like VWMS bushings. Do they still rotate in sheer like soft rubber or spin like poly? If they do behave like soft rubber bushings, their sheering will generate a larger torque than a soft rubber bushing that tries to resist the suspension movement. Is this torque strong enough to not allow full droop like you quoted above for the poly bushings? Just curious if VWMS bushings and other hard rubber bushings have any downfalls (excluding comfort of course).
Lastly, does anyone know if VWMS bushings are still available for MK4 front control arms (last I heard was that they were made for the MK3 but also fit the MK4)?


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## crazycommie (Jun 14, 2005)

*Re: Why (Rear) Poly Bushings Are Bad (Ceilidh)*

do you remember the article where one guy desicribed how to make polyeurathane engine mounts using lowes polyeurathane I want to make them but I can't seem to remember where the article was or who created it thanks


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## Ceilidh (Jan 7, 2004)

*Re: Why (groftja)*


_Quote, originally posted by *groftja* »_.....I have a question about hard rubber bushings like VWMS bushings. Do they still rotate in sheer like soft rubber or spin like poly? If they do behave like soft rubber bushings, their sheering will generate a larger torque than a soft rubber bushing that tries to resist the suspension movement. Is this torque strong enough to not allow full droop like you quoted above for the poly bushings? Just curious if VWMS bushings and other hard rubber bushings have any downfalls (excluding comfort of course).......

Sorry groftja,
I really don't have any experience with VW bushings. In general terms, all the rubber bushings I'm aware of (or have worked with) rely on torsional shear (among other things, the rubber is "sticky" and can't slip in the way that the poly and delrin bushings are intended to). As for not allowing full droop: again, I know nothing of the VWMS items, but in general rubber bushings can support some load if they're torqued down in the wrong position (a classic error is to tighten the bolts while the car's still up on a lift), which will affect ride height....but the bigger concern there is usually premature breakdown of the rubber if they're "preloaded" in that fashion.
Hopefully someone who's used the VWMS bushings can tell you more!
- C


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## Mr Black (Jan 20, 2002)

*Re: Why (Ceilidh)*

This subject is of intense interest to me as I am about to install the FULL poly rear beam bushings in my Mk2. I understand the points about the poly bushing rotating about the metal pin and causing a lot of friction, however I can't help thinking that with the right kind of lube, and possibly regular grease applications (not that hard a job as I see) this would prevent the kind of friction being described.
Something else that has been raised before is the fact that because the action of the torsion beam necessarily causes some twist in the bushing, the poly bushings will eventually start rubbing and binding against the bracket in which they are located. Again, I think to myself that careful greasing might help prevent this.
I've heard word of mouth testimony that the full poly units are really not as bad as Shine and others make them out to be, and quite frankly, when they cost about $35-40 US compared to the $275 or whatever for spherical units, I'm going to give them a try. Stock rubber bushings are just not an option for me anymore- my car wags its tail like a hyperactive German Shepherd. 
Picture a modern performance motorcycle with soft-ass rubber swingarm bushings.....you could not ride the thing due to the inevitable wagging motion once you started putting it through the corners. I know the bike swingarm is different than our trailing arms due to the fact that it moves as one piece only, not two independent wheels one at the end of each arm, but honestly, I have aftermarket springs and a 28mm rear bar....I doubt the range of motion is SO large that the bushings will see a great deal of twisting.
Time will tell I guess- I'm prepared to be wrong


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## yellowslc (Aug 29, 2000)

*Re: Why (Rear) Poly Bushings Are Bad (Ceilidh)*

I have used the vwms rear beam and LCA bushings in corrados. They were cast from the same molds as the OEM bushings using 80 shore rubber. As of a year ago, no more mk2/mk3/corrado front pivot LCA or rear beam bushings could be located. You also had to fully trust your source as the oem part #'s were in fact cast into these bushings as well!
Robert


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## pyce (Nov 7, 2001)

*Re: Why (Rear) Poly Bushings Are Bad (Ceilidh)*

Hope this helps some ....
The bushings are actually missing from the model on purpose, so it is easier to see how the outer and inner parts move in relation to each other.
This is just a concept, sort of work-in-progress. The real rear suspension is not exactly as seen here, but the geometry we have now is quite right for this exercise.
Note: The animation is very heavy, so wait until it loads well enough to be smooth and fast.
This is 5 degree roll to the right and then 5 degree roll to the left, for a total of 10 degrees, which is kind of the maximum on street tires, if not two-wheeling.


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## pyce (Nov 7, 2001)

*One Wheel Bump ...*

I guess the rolling scenario is not so convincing, so here is a "one-wheel-bump" scenario in which the "body" stays firm, only the right arm moves up and down as if we would have a one-wheel bump. Guess it is easier to catch the bushing movement now.....
Note: Wait until the animation loads to full speed.


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## supersonico (Aug 10, 2003)

Peter, it would be easier for us to see how the inner and outer parts interact on your first example´s animation if you were to keep the "body" (red bar) still and sway the torsion beam up and down, instead of the other way around. That´s precisely why it´s easier for anyone to see how the bushing moves in the second example, you´ve got a steady point from which you can accompany the beam´s support position. That´s if what I propose is at all possible, of course.
Cheers


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## pyce (Nov 7, 2001)

*One Wheel Bump - Zoom In*

Zoom-in here, so it is easier to see the bushing's movements....








On the first animation it is not so easy to see those things, as the purpose of that piece was not related entirely to this topic. It was built to observe the camber and toe changes during roll.


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## phatvw (Aug 29, 2001)

*Re: One Wheel Bump - Zoom In (pyce)*


_Quote, originally posted by *pyce* »_
On the first animation it is not so easy to see those things, as the purpose of that piece was not related entirely to this topic. It was built to observe the camber and toe changes during roll. 

Nice diagrams Peter! Solidworks?








If I am looking at this the right way, then the outside-rear tire goes toward positive camber while the inside-rear goes toward negative camber?
This assumes that there is a compressible bushing in there, correct? Does a racing bearing (like Shine) constrain the motion of the trailing arm to just a simple rotation around an axis which parallel to the stub axle, rather than the offset rotation we see here?
Can you make a diagram of the same rear-end with the shine bearings or equivalent?


_Modified by phatvw at 2:15 PM 8-15-2005_


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## pyce (Nov 7, 2001)

*Re: One Wheel Bump - Zoom In (phatvw)*


_Quote, originally posted by *phatvw* »_If I am looking at this the right way, then the outside rear-tire goes toward positive camber while the inside-rear goes toward negative camber?

Correct. If you observe carefully, you could even see the toe changes. Those are more difficult to see as the perspective is strong enough to skew them, but they are there.
Solid Works can not twist in the way needed for this, and its Dynamic Works package does not simulate rubber bushings, so it is all done manually in a separate package that allows global deformation.



_Modified by pyce at 2:28 PM 8-15-2005_


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## Mr Black (Jan 20, 2002)

*Re: One Wheel Bump - Zoom In (pyce)*

Thank you SO much for making these models visible. While I understand the limitations of poly given the nature of the torsion beam's range of motion, I think I'm going to try them anyways, and if the bushings get chewed up or the suspension action ends up being wonky, I'll just replace them.


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## rracerguy717 (Apr 8, 2003)

*Re: One Wheel Bump - Zoom In (Mr Black)*


_Quote, originally posted by *Mr Black* »_Thank you SO much for making these models visible. While I understand the limitations of poly given the nature of the torsion beam's range of motion, I think I'm going to try them anyways, and if the bushings get chewed up or the suspension action ends up being wonky, I'll just replace them. 
 You can show the people the water , but you cant make them drink it .







Great job peter http://****************.com/smile/emthup.gif Bob.G


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## pyce (Nov 7, 2001)

*Re: One Wheel Bump - Zoom In (rracerguy717)*

Mistakes are very important part of any learning process. Real life experience is something no text or animation can replace.


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## briang (Mar 10, 1999)

*Re: One Wheel Bump - Zoom In (pyce)*


_Quote, originally posted by *pyce* »_Mistakes are very important part of any learning process. Real life experience is something no text or animation can replace. 
 Wow. Pyce just described my entire life.








Excellent work on animation.


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## SnowGTI2003 (Jan 8, 2004)

*Re: One Wheel Bump - Zoom In (briang)*

Fantastic work. http://****************.com/smile/emthup.gif


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## Mr Black (Jan 20, 2002)

*Re: One Wheel Bump - Zoom In (rracerguy717)*


_Quote, originally posted by *rracerguy717* »_ You can show the people the water , but you cant make them drink it .









Ya ya, I know, the only reason I'm willing to do it is because I have had other people (who seemed inteligent and credible) report that there is a tangible improvement without any of the dreaded bind and destruction that theoretically should happen with a poly bushing.
Hey if they suck, I'll provide photo proof and testimony and then the matter can be sealed forever


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## Vr6Fidelity (Oct 4, 2001)

*Re: One Wheel Bump - Zoom In (Mr Black)*

Why don't you apply the appropriate stiffness and damping values to the constrained connections? It appears to me the the bushings mount at the OD is not constrained to be concentric with the pin. It appears to be constrained as a shpereical joint, when its intention is to be purely rotary. I am aware the bushing has a stiffness's in this direction, but it is quite high especially with poly. The stiffness's in the rotational direction is close to zero, therefore the bushings job is to convert most of those conical and neutating forces into more rotational displacement. This is the bushings intended purpose, it holds the components in a certain geometric locations, and resists deflection in certain directions. It is the reactionary force applied by the bushing the bends the axle. In your animation it appears the tail is wagging the dog.
It is also important to note the magnitude relationship between the stiffness's' of the torsion axle vs the bushing. For example, why are the bushings tilted at an angle? Im going out on a limb here but i would bet that upon full calculation of Von Meiss' combined stresses on the axle, with one wheel displaced, that the pin is oriented so that the forces applied to the bushing are as close to pure moment as possible.
The solid-works is sweet BTW. 


_Modified by Vr6Fidelity at 6:02 PM 8-16-2005_


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## Ceilidh (Jan 7, 2004)

*Re: One Wheel Bump - Zoom In (Vr6Fidelity)*

Hello Vr6,
Excellent points and questions! You've hit the nail squarely on the head, in highlighting a basic problem for those attempting to use poly bushings in the main trailing arm bushings: as you point out, the poly "tries" to convert the general forces into rotational displacement, whereas the geometry prevents such simple rotation. The result is extreme binding (see quotations in first post) and rapid degradation in field use.
If you don't mind, we''ll use the text of your post as a framework for addressing these issues, as the discussion might be of interest to the non-engineers following this thread. We'll start from the top:









_Quote, originally posted by *Vr6Fidelity* »_Why don't you apply the appropriate stiffness and damping values to the constrained connections? It appears to me the the bushings mount at the OD is not constrained to be concentric with the pin. It appears to be constrained as a shpereical joint, when its intention is to be purely rotary.....

Absolutely correct! The bushings are constrained as a spherical joint, and the cylindrical shapes are drawn in to demonstrate the distortion that a cylindrical bushing must undergo in normal use. Track-based Golf/Jetta racers successfully use spherical joints in the main trailing arm pivots, and the OEM vehicle employs large rubber bushings that can easily accommodate the deformation -- and both bushing types (OEM rubber and track-based spherical) work well in the real world. Poly, on the other hand, has some problems...

_Quote »_ 
..... I am aware the bushing has a stiffness's in this direction, but it is quite high especially with poly. The stiffness's in the rotational direction is close to zero, therefore the bushings job is to convert most of those conical and neutating forces into more rotational displacement. This is the bushings intended purpose, it holds the components in a certain geometric locations, and resists deflection in certain directions.....


And herein is the primary problem with poly (in this particular application): unlike OEM rubber, the poly has "quite high" compressional stiffness (i.e., it doesn't like to be squeezed!); and unlike spherical, it readily allows rotation only along a single axis -- which in this situation is not aligned with the (changing) axis about which the suspension wants to rotate. The result is extreme binding: whereas the OEM and spherical bushings allow the trailing arms to move as they are geometrically constrained, the poly tries to force them to move in a direction at odds with the basic geometry. When that happens, something has to give....

_Quote »_
....It is the reactionary force applied by the bushing the bends the axle. In your animation it appears the tail is wagging the dog.


I'm not sure that Peter would quite describe this model as one of the tail wagging the dog(!), but if we were to keep with this imagery, we have the body of a chihuahua connected to the tail of brontosaurus.








On one of Peter's modeling experiments (unposted), he wanted to see what what happen if he had the bushings "force" a simple rotational motion. The result is exactly what Vr6Fidelity predicts: if the trailing arms are to move at all -- that is, if the suspension is to do what suspensions are supposed to do: let the wheels move up and down -- the beam (i.e., the "twistbeam" connecting the two trailing arms) must bend. In fact, it has to bend a lot. So is this what happens?
Now, all those of you who have ever hefted a VW rear twist beam will know that it's a substantial piece of metal. Moreover, it's a substantial piece of metal arranged as a large-dimension "C" channel -- one that readily twists, but which strongly resists bending along any plane. When this roughly 4-foot giant crowbar meets up with a puny poly bushing, the result is pretty much what one would expect: the crowbar remains essentially straight (one can imagine it uttering a scornful laugh), and the bushing cries uncle.
Sorry, got carried away with the imagery there.







More prosaically, for suspension movement to occur with a poly bushing (or any bushing that tries to constrain the Golf/Jetta trailing arm to move in a single plane), either the bushing has to compress, or the twist beam has to bend. If push comes to shove, the beam is going to win (hands down), but in practice the bushing gets out of its quandary by refusing to play the game: because it resists compression, and because the beam won't significantly bend, the suspension in effect locks up and refuses to move. That is why the person quoted in the first post reported that his wheels would not drop when he jacked up his poly-fitted car, and that is why poly bushings (in this suspension) pivot yields such a rock-hard ride: it's not only that the poly transmits more impact harshness than does OEM rubber (note that the poly is reported to ride more poorly than do spherical bearings, which absorb NO impact harshness whatsoever), but more critically, the poly bushings don't allow the wheels to deflect upwards when encountering road bumps.
Now, lest anyone feel attracted to the "stiff, race-car!" implications of a suspension that won't, well, suspend, please reread the second quotation in the first post: under repeated impacts, with the poly bushings fighting the twist beam, eventually (reportedly fairly soon) the poly loses: it begins to break down, passing through an interval where it has degraded enough that it kind of sort of approximates what the OEM rubber bushing does for 100k miles, and then passes onwards into a noisy, clanky, loose-fitting mess.

_Quote »_ ....It is also important to note the magnitude relationship between the stiffness's' of the torsion axle vs the bushing. For example, why are the bushings tilted at an angle? Im going out on a limb here but i would bet that upon full calculation of Von Meiss' combined stresses on the axle, with one wheel displaced, that the pin is oriented so that the forces applied to the bushing are as close to pure moment as possible.

As just noted, a C-section torsion axle is pretty darn stiff under bending loads! But that leads to the next question cited above (and it's a good one): just why, oh why, did VW orient the bushings at such an odd angle?
Well, who knows?







None of us works for VW, and yours truly is just going on Peter's Solidworks models. But we don't need a full stress calculation to see whether it's primarily to align the rotation on one-wheel bump: if that were the underlying reason, we would next have to ask how VW managed to ignore 2-wheel bumps! (Maybe sometime Peter could post up an animation showing how the bushings move on a 2-wheel bump, but for now, one can take a look at the hinges on an ordinary household door : there are typically three, all of them in line, and it should be evident that were one to unbolt one of the hinges and remount it at an angle, then the hinge would tear off the moment the door is swung open). No, the angle of the bushings seems to be associated with something else entirely:
If I (Ceilidh) had to guess, the bushing angle is related to three separate observations:
1) As has been oft observed, the OEM trailing arm bushings are very, very large -- surprisingly large, in fact. Its size allows it to accommodate twisting motions (as discussed above), true, and it might permit better absorption of vibration and impact -- but it also allows significant distortion along the pivot axis. That is, there's sideways "slop" along the bushing, which is forever driving the autocrossers to distraction, and VW seems to have made no attempt at restricting it....

2) As has been oft reported, replacing those bushings with metal spherical bearings leads not only to better handling precision, but seemingly better neutrality and less understeer. That is, Vortexers who switch to spherical (if I remember the posts correctly) often report reduced understeer -- even when springs, shocks, etc. remain unchanged....
3) When the Golf/Jetta IV came out, VW made a bit of fuss about a "Track Correcting Axle", which nobody seems to have understood (has anyone seen an explanation of it? If so, do please post it up!).

In any case, putting #1,2,3 together with Peter's model makes for an interesting observation:
A) Take a look at the red bar in one of the animations. The red bar is a stand in for the chassis of the car. Imagine what happens in a left-hand corner: centrifugal force pushes the red bar towards the right (or, if your physics teachers spent a lot of time convincing you in your youth that centrifugal force doesn't exist (it does in a non-inertial frame, but that's another discussion!!), you can view it as the silver axle assembly being pushed to the left, to effect the centripetal acceleration....).
B) With spherical bearings, the bushings resist the lateral force. But with the large OEM rubber bushings -- which can distort along-axis -- the red bar (i.e., the chassis) can shift to the right, relative to the axle assembly. (Or alternatively, the axle assembly shifts to the left, relative to the chassis.)
C) If the bushings were not angled, but instead simply sat in a simple transverse alignment, the axle would shift sideways, and (to a gross approximation) there wouldn't be much to write home about. But with the angled bushings, look what happens:
D) As the right hand axle bushing shifts leftwards, it also (because of the angled axis) shifts forwards. Similarly, the left hand bushing shifts leftwards and rearwards.
E) The result is an axle assembly that steers the rear wheels towards the inside of a hard corner: that is, the rear wheels turn in a direction that promotes understeer. For a road car, this is a very nice thing! Road car designers (as discussed at length in last year's Shine/Koni/Bilstein thread) are forever wary of paying customers spinning off the road and over high cliffs, and this cornering-induced understeer is a handy tool: with it, you can give the car a little more neutrality at low g-forces (which makes for sharper transitional handling and a nicer balance at normal street speeds), whilst maintaining enough stabilizing understeer under extremis to keep untrained drivers from spinning off.
F) Replace the OEM bushings with spherical, and you don't get the shift -- ergo, less understeer at the limit.
Whoops -- have to run!! Perhaps more next week...Vr6, thanks for the insightful post, and please everybody have a great week. Cheers!
- C



_Modified by Ceilidh at 7:52 PM 8-16-2005_


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## Vr6Fidelity (Oct 4, 2001)

*Re: One Wheel Bump - Zoom In (Ceilidh)*

Perhaps the most well thought out, factually correct response ever posted on the tex. bravo. 
Oh and am i ever glad im lazy and haven't poly'd my car yet!


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## pyce (Nov 7, 2001)

*Two Wheel Bump ....*

Here is a pure Top View (no perspective) of the Two Wheel Bump. I guess this would make it even easier to observe....
At this point it is very easy to imagine how the spherical bearings would work, but if someone send me a picture of spherical bearings on an A4 VW so I can see how they are fixed to this assembly - I will model and animate them.


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## Mr Black (Jan 20, 2002)

*Re: Two Wheel Bump .... (pyce)*

The A4 beam seems to be an even worse candidate than a Mk1/2/3 due to the fact that it _starts _with the bushings having offset axes of rotation. Even if the beam travels uniformly (pure bump on both sides as in the above animation) the damn things misalign off their inital axis. I'm pretty sure this doesn't happen on the earlier cars, which suggests to me that the twisting when there's _independent_ wheel motion would also be less, although still present. Any thoughts?


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## pyce (Nov 7, 2001)

*Camber Curves Rear Suspension VW A4*

Here are the camber curves we get on the rear of an A4 VW with body roll. It is pretty interesting to see how linear the gain/lost is and how the sum of the two number per each degree of roll always gives more or less the same total number. Simple and predictable. Maximum body roll for this exercise was set to 5 degree. The car can roll more, but the beam can not as it is limited in compression and extension by the bump stops and dampers....


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## Ceilidh (Jan 7, 2004)

*Re: Camber Curves Rear Suspension VW A4 (pyce)*


_Quote, originally posted by *pyce* »_Here are the camber curves we get on the rear of an A4 VW with body roll......

Thanks for posting this up, Peter(!)
Just wanted to point out to everyone that as the car rolls 5 degrees, the wheels gain only about 3.3 degrees of camber (going from -1.65 to +1.62). This type of gain is one of the respects in which a "Twist Beam" differs from a pure trailing arm suspension:
On the Forum, you'll sometimes see an assertion that "because the Golf/Jetta has a trailing arm suspension, the wheels lean with the chassis", or something to that effect. In a pure trailing arm setup, the wheels do simply roll over as the chassis rolls (e.g., if the car rolls 5 degrees, the wheel camber changes by 5 degrees as well), but the Golf/Jetta twist beam is different: in two-wheel bump, it's like a trailing arm suspension, but in roll and one-wheel bump, it behaves as a semi-trailing arm suspension (i.e., the way the rear of an old BMW behaves). One aspect of a semi-trailing arm is the sort of camber gain seen in Peter's graph, where the rear wheels take on camber less rapidly than one might expect.
Cheers, everyone!
-C



_Modified by Ceilidh at 5:49 PM 8-18-2005_


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## rex_racer (May 19, 2001)

*Re: Two Wheel Bump .... (pyce)*


_Quote, originally posted by *pyce* »_At this point it is very easy to imagine how the spherical bearings would work, but if someone send me a picture of spherical bearings on an A4 VW so I can see how they are fixed to this assembly - I will model and animate them.

are you talking about this?


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## pyce (Nov 7, 2001)

*Re: Two Wheel Bump .... (rex_racer)*

Yes! Do you have at least another one from a different angle, so the models are more accurate?


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## rracerguy717 (Apr 8, 2003)

*Re: Two Wheel Bump .... (pyce)*


_Quote, originally posted by *pyce* »_Yes! Do you have at least another one from a different angle, so the models are more accurate?
 Here you go peter , i believe this is ths similar design , just for the other mounts.







Bob.G http://forums.vwvortex.com/zerothread?id=1663311


_Modified by rracerguy717 at 7:26 PM 8-18-2005_


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## phatvw (Aug 29, 2001)

*Re: Two Wheel Bump .... (rracerguy717)*

I'm confused.
What does the "spherical" refer to in the term "spherical bearing".

Does it refer to the individual ball bearings that are spheres, or does it refer to spherical movement as in something like a ball joint where there are 2 dimensions of freedom?
I rebuilt my bicycle wheel bearing recently and inside there are two metal rings (are these "races"?) with about 10 little ball bearings covered in grease in between. Is that a spherical bearing because there are spherical balls inside? Somehow I think not...























edit: ok I think I'm getting a better picture, but Maybe Peter or Winston can give a better explanation...
http://www.aurorabearing.com/page5.asp



_Modified by phatvw at 4:52 PM 8-18-2005_


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## Ceilidh (Jan 7, 2004)

*Re: Two Wheel Bump .... (phatvw)*

Hello Phat!
How can I resist answering a post that mentions bicycles?








Yes, the terminology can be a little confusing, but a spherical bearing (in this context) is generally taken to mean a bearing that allows rotation along all three rotational axes (as opposed to an ordinary bearing's single axis of rotation). In construction, it's sort of like a ball & socket, though often the base of the socket and the ball have a hole so you can pass a bolt through (e.g., as in the aurora bearings shown in your link, where the "hole" is so large that the bearing is symmetric); in any case, the "spherical" part is the central ball of the bearing.
Your bicycle hub bearing, by the way, is a single-axis ball bearing, and typically the balls, which are held in circular metal "cages", sit between an outer bearing race and a "cone" that forms the inner race.
As a completely non-VW aside, if your hubs have the metal cages, you can often dispense with the cages entirely and just put the balls in loosely (the cages are primarily there to ease assembly in the factory); with some hubs, your rolling friction will actually go down if you do so.
And, as a final aside: what year was your bike built? Rebuildable ball-bearing hubs do still exist, but they're kind of retro (at least for the mass market).


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## phatvw (Aug 29, 2001)

*Re: Two Wheel Bump .... (Ceilidh)*

Thanks Ceilidh! Thats kinda what I thought regarding the spherical bearings but I just wasn't sure. I was also thinking of the type of bearing where there are no balls and just a guide sleeve and just one axis of rotation as in a camshaft guide/bearing or a foosball game table. Thats what got me confused about the spherical term.
My bike is a hybrid mountain/roadbike with 1.5" tires, a slightly curved fork, and upright handlebars. I think its about 6 or 7 years old bought in Canada under the Norco brand. Anyway, I had never seen the inside of a wheel bearing before, but since the wheel wasn't spinning like it used to - it felt like there was sand in there - I opened it up to see what was wrong. I don't think mine has the cages that you spoke of. The balls were held in only by the grease once the outer race was removed and one actually fell out when I first opened it up. I cleaned up some of the gunk in there and it works a little better now, but I think I need to do a more thorough job and re-pack it with new grease or something. Its remarkable how well those little 2mm balls worked for 7 years!
Ok enough off-topic stuff. Back to cars.
From the looks of the MkV Jetta article on the vortex front page, it appears that the new platform is using new bearing designs. Do you suppose these are these spherical? Anyone have a good diagram of the new chassis?
http://www.vwvortex.com/artman...shtml

_Quote, originally posted by *vortex* »_
Chassis - Complex multi-link rear axle optimises comfort and agility
FRONT AXLE - Greatly optimised strut front axle: Even more agile, precise and comfortable than before
The strut front axle with lower wishbone from the Bora has been extensively revised in numerous areas for use in the new Jetta. Greater transverse stiffness at the wheel contact point ensures improved steering precision. The stabiliser bar attachment reduces the body roll. The ride and driving comfort benefits from the optimised angled shock absorbers, the new *bearing* concept of the lower transverse link and the separate mounting of the spring and damper on the strut tower.
MULTI-LINK REAR AXLE - Innovative suspension and ride comfort plus perfect handling properties
The truly innovative multi-link rear axle in the new Jetta allows both superior driving comfort and perfect handling properties. Thanks to this axle concept, the longitudinal and transverse dynamics of the new model can be optimised more or less independently of each other. Thanks to their carefully configured bearings, the three transverse links define the wheel variables like the track and camber that allow safe and agile cornering. The trailing link with its large-sized *bearings* define the longitudinal movement of the wheel. Thanks to a slight toe-in angle, they also help prevent brake dive. In this way, they ensure stable road holding even when you brake in curves. Thanks to its refined kinematics or elasto kinematics, the Jetta’s multi-link axle also easily meets the requirements for different loading states.


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## GTIspirit (Dec 13, 2002)

*Re: Two Wheel Bump .... (phatvw)*








to *pyce* for those fabulous animations. It's a tough concept to understand and once you do understand it you see why poly is terrible for the rear trailing arm, as well as the rear bushing of the front control arm, and possibly also the front bushing to a lesser degree. That being said, the best options to maintain correct geometric movement are the aforementioned spherical bearings, aka monoball, or OEM style rubber bushings. The Shine and Bildon rear bearings are so darn expensive, and replacement rubber bushings are not available for the Mk2 rear trailing arm, what's a guy to do?


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## Mr Black (Jan 20, 2002)

*Re: Two Wheel Bump .... (phatvw)*


_Quote, originally posted by *phatvw* »_
From the looks of the MkV Jetta article on the vortex front page, it appears that the new platform is using new bearing designs. Do you suppose these are these spherical? Anyone have a good diagram of the new chassis?


Strongly doubt it- despite the fact that they use the word "bearing" in the press release, I don't think any manufacturers use sphericals as OEM. Rubber, in varying levels of stiffness, is the chosen material because it allows some compliance to absorb bumps, whereas sphericals offer none.


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## SRSVW (Jun 28, 2001)

*Re: Two Wheel Bump .... (Mr Black)*


_Quote, originally posted by *Mr Black* »_Strongly doubt it- despite the fact that they use the word "bearing" in the press release, I don't think any manufacturers use sphericals as OEM. Rubber, in varying levels of stiffness, is the chosen material because it allows some compliance to absorb bumps, whereas sphericals offer none. 

Mostly true,however at least Porsche and maybe others have used sphericals in OEM apps. Check out the lower control arm in the rear of a 993 and maybe the 996. These are truly exceptions and even then they combine them with rubber on the other end.

Dick Shine


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## sicks (Jun 7, 2003)

*Re: Two Wheel Bump .... (SRSVW)*

wow the poly debate is still goin' on ? for the past 3 years?
poly binds... get over it. why do you think it squeaks unless u lube the **** outta it ? cuz it's seperatin' from where it sticks to itself when squeezed... (aka binding)
why would u want an added forces to hinder your suspensions movement when it's already fightin' plenty as is... ? 
POLY WAS A TREND... now it's an obsolete debate... and the only reason poly was a trend to begin with.. is because the uneducated american customer will buy anything if it looks good in the advertisement (this is um.. called... effective marketing)... 
if poly was the ish.. it would market itself... the only place poly should be on you car.. is your front and rear bumper covers.


_Modified by sicks at 1:33 PM 8-20-2005_


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## Ceilidh (Jan 7, 2004)

*Re: Two Wheel Bump .... (pyce)*


_Quote, originally posted by *pyce* »_Here is a pure Top View (no perspective) of the Two Wheel Bump. 










[NOTE to those listening in: if the following gets too technical, please ignore it! If Peter goes along with this and comes up with a future animation (or 3), we'll put up an accompanying text in plain English. For now, though, we're just talking technical shop, so apologies if it proves unintelligible....]








.
.

Hi Peter!
Hope you're having a good weekend!
I've a request for when you next have some modeling time -- no hurry at all; I know you're busy with several other things, so this is low priority! But when you do have a chance, and if you think it'd be an interesting project, here's my request:
1) Could you please take the above animation (non-perspective top view of rear axle assembly & chassis mount), and "freeze" it (i.e., shut off the animation) in the neutral, non-bumped position...
2) ...and then put in a new (slow) animation, showing what happens when the OEM bushings distort axially under side loading?
3) Specifically (and ideally), the animation would start in the neutral, straight-ahead position, with both wheels tracking straight forward (perhaps some lines aligned with the (invisible) tires would be helpful here...).
4) Then, keeping the red "chassis" bar fixed, slide the silver "axle" assembly over to the right (corresponding to the lateral movement of the assembly in a hard, right-hand corner).
5) As the axle displaces, please zero out the radial distortion in the bushings, and keep all the bushing movement in the axial direction (relative to the bushing); in effect, the silver bushing housings should stay concentric with the red "pins", and will simply slide along them.
6) When the axle has slid all the way to the red-bar stops (and feel free to exaggerate the motion, to make it easier for people to see), maybe then stop the animation, and let people see how the rear wheels have now turned to the right (i.e., towards the inside of the corner).
7) As a side note, don't worry about having the wheels deflect in roll -- the idea here is just to isolate the rear-steer effect at zero bump/ zero roll!
Sound good? If it's too much work, or uninteresting, or if you simply haven't time with everything else (e.g., looking forward to the next damper test!), please do ignore this request. Regardless, thanks very much again for all the great work, and hope you're having a fine weekend. Cheers!
- W
.
.
P.S. -- if we really want to get fancy (in the future), we can maybe explore why these bushings are called "track correcting" (which is probably marketing-speak for "steer correcting"):
A) In a conventional twist-beam (i.e., one where the red "pins" are not angled, but simply run straight across, in line with one another), radial distortion in the OEM rubber bushings will cause an oversteering deflection of the rear wheels (note: we neglected the radial distortions in the above request, but in practice it'll be there).
B) Showing the above would require a separate animation, but basically as the wheel hubs shift rightwards in a right-hand corner (on a normal, non-angled twist beam), they induce a counter-clockwise torque/moment that will rotate the assembly, steering the wheels over to the left.
C) Let's call the two phenomenon "I" and "II":
"I" is the idealized case covered in the initial request: zero radial deflection, significant axial deflection, angled pins. "I" produces deflection understeer.
"II" is the ordinary-axle situation: significant radial deflection, irrelevant axial deflection, straight transverse pins. "II" produces deflection oversteer.
D) What appears to be happening at the rear of our cars is a combination of "I" and "II": radial deflection in the OEM bushings is attempting to induce oversteer, whilst axial deflection on the angled pins is trying to induce understeer. In effect, the angled pins on our cars serve to counteract, or "correct" the oversteer effect that would normally take place (note: that must be the origin of the marketing-speak "track correcting rear axle").
E) As a final note, it seems that by playing with the pin angle and with bushing geometry (which will determine the relative proportions of axial vs. radial distortion) , VW can dial in however much deflection-understeer, -oversteer, or -neutrality it wants. The final choice is presumably a matter of tuning the rear to the characteristics of the front suspension....
Rather a clever design -- very simple, robust, and inexpensive, with more tuning parameters than at first meet the eye.










_Modified by Ceilidh at 11:13 AM 8-20-2005_


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## pyce (Nov 7, 2001)

*Re: Two Wheel Bump .... (Ceilidh)*

Here...








This is top view and the car is turning left, therefore the red bar (the chassis) is pushing towards the right. Due to the geometry, we have the rear beam steering towards the left. This is just a concept, actual distortion may be less.
I can do some before and after, but guess it is pretty clear. It is not huge amount of steering, the CAD shows about half degree for the shown distortion, which in real life could be less. There is not such distortion with spherical bearings.
Note: It is animation, wait until it loads for full speed.


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## Mr Black (Jan 20, 2002)

*Re: Two Wheel Bump .... (pyce)*

Well, moving out of the empirical realm and into the subjective, I installed my Energy Suspension bushings this week and I must say, barring any future wear and tear, that I am VERY happy with the way the car responds now. The ass end feels way more connected, even to the extent that I can feel it through the seat in moderate cornering, and the wag-the-tail sensation in sweeping and decreasing-radius corners is MUCH reduced.
I have not noticed any "bind" to speak of..........the car feels much more precise than before as opposed to less.
Now, I will be keeping an eye on the condition of the bushings as time goes on...who knows, they may in fact degrade quickly. I asked my mechanic to lube them carefully, on the sleeve and also on the sides where the bushings contact the bracket. I will keep everyone posted on any relevant findings.


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## 7thGear (Sep 20, 2002)

*Re: Two Wheel Bump .... (Mr Black)*

just wanted to bring this back from the dead, as i believe it requires due consideration in light of where this forum is heading
(ie, enlightment...







)


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## JPX (Nov 6, 2005)

*Re: Two Wheel Bump .... (7thGear)*

I agree! This type of modeling is very useful for showing how things work on these cars. I had no idea that is how a beam worked - more familiar with a-arms and the like. Perhaps a similar exercise for the front suspension would be very educational for those interested in lowering/performance upgrades/clearance visualization.


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## seesquared (May 4, 2004)

*Re: Two Wheel Bump .... (JPX)*

It has already been done and it in the FAQ.
MkIV Suspension Geometry Thread


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## fckreher99 (May 15, 2003)

*Re: Two Wheel Bump .... (seesquared)*

i suppose my question would be, where one might find spherical bushings for the rear beam of a golf/jetta.


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## Jezztor (Nov 9, 2002)

*Re: Two Wheel Bump .... (fckreher99)*


_Quote, originally posted by *fckreher99* »_i suppose my question would be, where one might find spherical bushings for the rear beam of a golf/jetta.
















http://www.srsvw.com
Good luck on the customer support though.


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## VWplaything (May 7, 2006)

*Re: Two Wheel Bump .... (Jezztor)*

First, kudos are still in order (IMHO) for the animation...That having been said, I'm new to the forum, and also to performance parts to a large extent, BUT I can give anyone still interested in the topic this two cents: 
I've run poly bushings on the A1 chassis for many years. Typically, all of the racing I do is illegal (no ****!), on winding back roads in hilly terrain with a lot of hard cornering at suicidal speeds - sometimes with only two wheels on the road (...now that's what I call LIVING). 
Rubber gets destroyed - and I mean destroyed - very quickly under these conditions, while the poly seems to hold up well. I realize this discussion seems to have progressed toward less linear designs in suspension, but I guess the point I'm raising is that a perfect model is what it is. 
Actual performance from one's suspension depends on a lot of external factors - including choice in tires and rims, road surface and condition, type of driving, weather and outside temperature, aerodynamics of the car, where your tools ride inside the car, the list goes on and on. Bottom line is, if you are pushing your VW to its potential, then expect to replace parts - and bushings are definitely no exception. All new bushings will increase that potential, all worn ones will decrease it - it's a no-brainer. Rubber may not wear and distort the same as poly, but once it has lost its resilience it's shot - no matter what it looks like when you tear down your suspension. 
The bushing's only purpose is to prevent the metal parts from failing under load. Properly lubed poly will do that at least as well as rubber any day - at least on the cars I've had - and in my opinion, the performance of new OEM rubber fades a lot quicker than poly. 
Now, not confuse anyone, but I'll say this as well: Generally speaking, I've had my best luck with OEM parts, when it comes to rear suspension. The biggest problem I've encountered with them is longevity. Again, if you're driving your VW hard on a regular basis, expect to replace parts - especially those that are DESIGNED to wear.
Make no mistake, rubber binds every bit as much as poly, and by most posters' testimony it's intentionally designed to do so. It is also a lot less stable by nature than poly. A rubber bushing that does not show wear may appear so because it is swollen from oil or other contaminants it may be subjected to. In addition, rubber is more prone to deterioration from salt, and to permanent distortion from stresses encountered under heavy load and/or age.
SO, what is better - rubber or poly? I guess that depends on your car, your style of driving, and the type of driving you do. Neither one is going to destroy your car unless you allow it to become excessively worn. If you're like me and can't resist the temptation to embarrass a V-8 on your way to work or trick a Honda owner into twisting his car, then poly may be the choice for you. If you're racing autocross and tearing your VW down regularly, then I'd recommend rubber 'cause it's cheaper and the performance is spot-on right out of the box.
Guess that puts my head on the chopping block....have at it


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## f1forkvr6 (Jun 10, 2002)

*Re: Two Wheel Bump .... (Jezztor)*


_Quote, originally posted by *Jezztor* »_http://www.srsvw.com
Good luck on the customer support though.

State-side, by phone or in person, it's pretty darn good


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## briang (Mar 10, 1999)

Stayin' alive bump...


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## phatvw (Aug 29, 2001)

*Re: (briang)*

ah
..ah
....ah
......ah


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## briang (Mar 10, 1999)

*Re: (phatvw)*


_Quote, originally posted by *phatvw* »_ah
..ah
....ah
......ah


And my initals are B G


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## ovlaicu (Mar 19, 2005)

*Rubber is better*

With not too agresive driving, but still, pretty spirited, I only got 30k km on a set of energy poly bushings for the LCA. 
They do stiffen the susspension, they fill great for the first few thousand clicks but then they fade. 
If I would take them to the track, or on a "nice" twisty drive...probably the wouldn't last for more the 2-3 days. TOPS. Rubber lasts for at least, easilly at least, 2-3 times more. 
A thought keeps bugging me. If you put the spherical bearings in there...since they have no lateral play at all, isn't it going to be easier to loose traction? since the wheel becomes so rigidly attached to the body...all the iregularities of the road have to be absobed by the tire, shock/spring and that's pretty much it. 
I donno if I make sense it words...but it makes sense in my head


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## ewongkaizen (Apr 19, 2002)

*Re: Rubber is better (ovlaicu)*


_Quote, originally posted by *ovlaicu* »_A thought keeps bugging me. If you put the spherical bearings in there...since they have no lateral play at all, isn't it going to be easier to loose traction? since the wheel becomes so rigidly attached to the body...all the iregularities of the road have to be absobed by the tire, shock/spring and that's pretty much it. 
I donno if I make sense it words...but it makes sense in my head

BUMP - I had to dig up this post to link it to another noob Q...
Buy going to sperical - you force the suspension to do its job. 
Instead of the suspension also being the bushings as well.
On a race car - you want to limit effects to what you are working on - i.e. the shocks and springs - and take out all the other side items so that you have fewer parameter to deal with in your already complex environment.
If your suspension was sucky and the wheel contact patch was being HELPED by mushy bushings.. you have other issues to address anyway.
On a seperate side note - There ARE people who run spherical bearings on DD cars... (but not me)


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## 94expload (Jun 21, 2007)

*Re: Rubber is better (ewongkaizen)*

What about poly mounts for the rear struts? are thoes ok? and i am asking about a MKIII car, since its a little different, but still a pivit point on thoes cars. Is it better for the stiffer poly, or the lose rubber?
It seams like with the poly they are smaller, and more upand down play when putting them in, were as the stock mount is nice and tight, no play anyway, untill under force.
sorry


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## DAVEG (Aug 14, 2001)

*Re: Two Wheel Bump .... (Ceilidh)*

Ceilidh, your comments make the rear suspension geometry much more relevent. I have a Mk1 and considered the rear less important. I concentrated on the front suspension understeer. I am wrong!
"...radial deflection in the OEM bushings is attempting to induce oversteer, whilst axial deflection on the angled pins is trying to induce understeer."
The rear exacerbates the front camber changes and induces heavy understeer. I changed the front Camber (-1) and wheel offset (+1/8) to help reduce understeer in SoloII. The biggest advantage came when these changes were combined with more toe out 1/4". IF I stop accellerating into a corner the front changes from zero toe out to 1/4" toe out...I break which maintains the toe out until I turn...rear rotates and then accelerate. If I stop the rear OEM bearing deflection then I can also reduce rear axel deflection inward on a turn. The rear helps the front.
Now if I use two rear links that tie the trailing arm ends to the center of the arm I can reduce deflection of the axel arm inward. Does this sound reasonable and does anyone have experience with this addition?


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## a2_cruiser (May 8, 2004)

*Re: Two Wheel Bump .... (DAVEG)*

this all hurts my head and i hate understeer so if my mk2 was ever to see track time it gets the extra 150 bux spent on bushings.


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## Tim.vw. (Dec 9, 2008)

Just read this who topic and go to check out shines website they closed last Friday fml, but FYI incase someone like me gets there hopes up, great read tho!


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## rex_racer (May 19, 2001)

a2_cruiser said:


> this all hurts my head and i hate understeer so if my mk2 was ever to see track time it gets the extra 150 bux spent on bushings.


In the case of the MK2, since the rear beam bushings do not travel in multiple directions, solid bushings are preferable, from poly to Delrin.


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## meboice (Mar 24, 2012)

And I pretty much follow that rule; in single axis articulation poly and delrin may be okay...multiple axis articulation rubber or heim joint...as long as the heim joint articulates with enough range to compensate for an entire suspension stroke.


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