RTAB on Z4M: bushings or limiter kit?

F

Franzino

Active member
I want to reduce the movement of the REAR TRAILING ARM of my Z4M. My 4M roadster is equipped with Eibach springs + AP brake kit + Strut Brace + 19" CSL wheels + Michelin Supersports…. In the dry months, my Z4M comes on track once a month..the rest of the time it's a normal street car.

I was thinking on going for the well know Powerflex items: http://www.powerflex.co.uk/black-series/product-details/Rear+Trailing+Arm+Bush/10113.html

Some people say it's not a good idea to fit Polyurethane bushings and its better to fit Trailing Arm Bushing Washers. For example these ones: http://www.vorshlag.com/product_info.php?cPath=1_106_111&products_id=59

Unlike other suspension bushing locations that only have one axis of rotation, swapping in excessively stiff replacement bushings using materials such as Polyurethane can and will cause suspension bind. The stock rubber M3 bushing is fairly compliant and effective when brand new but wears quickly over time, and doesn't cope with the added forces from race tires in perfect condition. Added wear adds excessive toe change under suspension movement, acceleration and braking. It is compounded greatly with additional power and grip from racing compound tires. If your stock RTABs have more than 20K miles and/or you've used the car for more than a season of racing, they are likely shot.

Many racers just blindly install polyurethane into this and all bushing locations as a "fix" for a worn OEM rubber RTAB bushing. Polyurethane is a bad choice for a bushing material if it has to deflect - such as in a multi-axis suspension bushing location like the RTAB. Rubber bushings + limiters or a complete replacement with a custom steel spherical bearing are the only two textbook choices for this location. We cannot count the number of times we have seen RTAB or front LCA failures on BMWs that were using poly in these areas - an expensive repair and dangerous racing situation. At the very least poly will add bind during significant suspension movement, and this can make the handling feel odd (unexplained oversteer) as well as add significant stress to the suspension-to-chassis mounts (which is how they can fail over time).

If you have a street car or dual purpose BMW you should always stick with OEM bushings and RTAB limiters, and even many race prepped BMWs use this setup with excellent results.
Click to expand...

They also sell Powerflex bushings, but have this note on the page:

Note: We recommend against running polyurethane in the RTAB location for E36/E46 cars due to the bind that can occur in a multi-axis bushing and do not offer them for sale.
Click to expand...

Turner Motorsport has also a RTAB limiter kit: http://www.turnermotorsport.com/p-964-turner-motorsport-rear-trailing-arm-bushing-limiter-kit-rtab-shim-kit.aspx
 
I had the same dilemma and have decided to fit new, standard bushes, together with the Vorschlag limiter kit. Will be in a better position to comment after that.
 
has to be limiter kit and stock bushes imo....


the poly bush in this area will make all sorts of noise... the limiter kit with the stock bush does exactly the same thing but allows silent working, and the oem bush for this part is cheap too... turner RTAB kit gets my vote, these arent cheap however at like 100 quid for 4 little blocks of alloy.. ///M tax sucks!
 
I'm fitting the Turner RTAB limiting kit too, probably next week. I researched extensively trying to find an answer to the polybush vs limiter argument - the most persuasive arguments supported the limiters (or spherical bearings).
 
I fitted Rogue Engineering street polybushes to mine about 6 weeks ago.

I'd bought them along with a load of other suspension bits and pieces, but debated whether or not to fit them because most information I read after buying them said OEM plus limiters was a better option.

In the end I decided to fit the polys (because they were just sitting around on the shelf doing nothing :) ) on the basis I could always fit new OEMs and get some Turner or Rogue Engineering limiters if I didn't like them.

I have to say I'm really pleased with them. Of all the mods I've done over the past 3 months or so (fitted KW V3 all round, Rogue Engineering rear shock top-mounts, Vibra-Technics engine mounts, front spacers, 4 wheel alignment) it is the one that has made the biggest difference to the way the car feels and handles.

My car had done about 27,000 miles before changing the RTABs. Before the change I was getting noticeable 'rear wheel steering' effects over undulations in the road - this became more noticeable after fitting the KWs. The new RTABs have really tightened up the back end and the impression is now one of sitting on top of a rear axle that is much more planted and stable.

With the RE street poly bushes, the ride is noticeably firmer than stock (which I like), but - in my view - not uncomfortably so. So far they make no noise whatsoever. RE's claim is that their polybushes are made with a small amount of silicone and a grease trap to eliminate noise (I slapped loads of grease in when I fitted them).

So far it seems to be working, but it is fairly early days yet. If they do become noisy, I'll just fit OEM and limiters to see what they are like (it was an easy enough DIY with a bush removal tool - wouldn't have fancied doing it without one).

In summary: I think doing something to the RTABs is a very worthwhile mod. I'm really happy with the RE polys, but can see how OEMs plus limiters would retain the stock level of ride comfort whilst improving control of the rear wheels over stock. Good luck - hope you like the mod. :thumbsup:
 
Has anyone got the measurements for these as I wouldn't mind having a go at making my own.
 
Went Rogue Poly bushes, no noise, ride firmed slightly however all positive and how it should be from the factory.
 
ITAG said:
Went Rogue Poly bushes, no noise, ride firmed slightly however all positive and how it should be from the factory.
Click to expand...

^ Totally agree... had mine fitted for a year now :thumbsup: :driving:
 
I've been driving with the powerflex ones for years now.
Excellent quality.
No noise what so ever. In fact my whole car is polybushed with powerflex and strongflex bushings, and it gives no noise at all. (I believe 21 bushings in total or so). So if you experience noise, you probably have it installed incorrectly.
 
Turn your E36 into the Ultimate Driving Machine that it was meant to be.

For Sale: E36 / E46 Syncro Design Works Rear Trailing Arm Bearings (RTABs) $199.99

(30% discount because they have scratches from where they were previously installed.)

Price: Retail $284.99

Condition: Installed only 1 month - almost brand new. Only marks on them are some anodizing is scratched from where they press into the Trailing Arms.

I have decided to sell my e36 M3. I have put it back to stock. I will be buying another one later. For now....I am selling my E36 / E46 Syncro Design Works Rear Trailing Arm Bearings (RTABs). They were amazing and since they were installed in my M3 I have never felt that sort of connection to the road in ANY vehicle. AMAZING upgrade. I had them installed for about a month. Ride was firm but not unpleasant. I need a car with a luxurious ride for my clients as I sell Real Estate so I am getting a newer 3 series and leaving it stock.

Retail Price for these is $284.99 at Harrison Motorsports.

Private Message me for more info & pictures.



From Harrison Motorsports:

Syncro Design Works' Rear Trailing Arm Bearing, BMW 3 Series, E36 / E46 and Z4
Snycro Design Works' rear trailing arm bearing updates and improves the rear suspension in BMW 3 Series E36 and E46, and Z4, by eliminating binding and deflection through adding precision and longevity.
Syncro Design Works RTAB's utilize an OE developed bearing, designed for long-life while offering full articulation for optimal suspension geometry.
While at home on the street, this bearing is precise enough for track duty. Syncro Design Works' own 410hp shop track/street car still has the original prototype bearing installed in 2009, with no measurable toe deflection.
Why Syncro Design Works' Rear Trailing Arm Bearings?
The trailing arm on the E36/E46/Z4 rear suspension attaches to the chassis just in front of the rear tire. The arm curves around the wheel, creating a pivot point which maintains toe-in as well as fixing the position of the wheels, front to rear. A stock rubber bushing wears over time, allowing deflection in the joint. The problem is compounded by performance upgrades such as increasing engine horsepower, increased grip of sticky tires and improved braking systems.
By maintaining precise control of the trailing arm, more aggressive alignment settings may be run, resulting in the car handling better without concern of 'rear steer' condition as a result of worn bushings.
Symptoms of worn bushings...
If your car is twitchy when braking, or experiencing a steering effect on acceleration, your RTABs may be at the end of their service life. Worn trailing arm bushings can create an undesired 'rear-steer'.
What makes Syncro Design Works RTAB’s special?
Syncro Design Works Rear Trailing Arm Bearings offer a range of multi-axial movement, where OEM bushings only pivot on a single axis, similar to a gate hinge in motion.
OEM bushings, even when new, allow more deflection than preferred for optimal performance and have a limited service life.
Syncro Design Works rear trailing arm bearings are lubricated and sealed for maintenance free operation, which makes them the last RTAB that vehicle will ever need.
 
http://www.turnermotorsport.com/pages/Instructions/E36_trailing_arm_limiter.pdf

For the 36 but exactly the same on our cars.
 
you didn't explain the prescribed pretension (by BMW) when fitting the limiters/original bushing.
 
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