Uprated rear trailing arm bushes and adjustable RTAB mounting plates

[B21]

The E89 suffers from rear wheel steer caused by the geometry of the rear wheels moving from toe in to toe out..as soon as rear toe points out stability is compromised with unpredictability..as you lift off then toe angle changes again..

The more power, the more aggressively applied the worse the problem…it’s an issue in all aspects of handling…other BMW guys have recognised this and almost all pre F series cars have solutions of varying solutions to this issue inherent in rear trailing arm designs..

When I tried to get the steering geometry set up we found that the toe in couldn’t be set to perfection due to limitations in adjustment of the stock rear trailing arm to chassis brackets.

In addition they observed that the trailing arm bushes fitted only a year earlier were showing signs of wear…

The E89 rear suspension is a complete copy of the E85/86 except that certain dimensions are altered as a result of track width changes.

The E85 boys have been changing their RTABs for a long time with all sorts of versions being used such stock, polyurethane and even roller bearings.

The issue for the E89 as well is that the whole rear wheel geometry and stability rests on the integrity of the bush and its relationship to the arm and bracket.

The problem is that with 400 BHP tugging at the bushes they deform under load and wear..in both cases the toe in fa tor changes..going to toe out..analogous to dynamic and unmanageable rear wheel steering.

To get round these issues I’ve bought some chunkier RTAB mounting plates that bolt to the chassis and have much greater adjustability.

To get round the distortion that happens to the RTAB there are various solutions..needle / roller bearings, polyurethane bushes and in this case a much uprated rubber based bush but with a focus on stability whilst still avoiding NVH induced issues.

Hardrace make these bushes for a wide variety of cars and other suspension related bushes..as well as needle roller solutions if you can cope with NVH.

I’ve got the bushes for the other linkages , 2 per side.

Since all these bushes during their installation process will affect the geometry I plan to get these done by the shop that then does the geometry adjustment..

Pictures show the stock bushes alongside their uprated cousins..

This set cost around £300 so not a cheap solution plus another £100 ish for the chunky brackets..

[KennyP]

I have the same set of Hardrace 7260 rear trailing arm bushes on the shelf at the moment
Im going to use them with RTAB limiters that i got from FCPEuro.
https://www.fcpeuro.com/products/bmw...-set-093031010
Have them on the shelf waiting to go in aswell.

And for the smaller bushings/ balljoints, i mean the upper and lower one on the trailing arm... i have Lemförder balljoints in the mail arriving next week...
Same parts as in this FCPEuro kit, minus the monoball RTAB:
https://www.fcpeuro.com/products/bmw...m-kit-rtabmbkt

I did consider going monoball RTAB-s at first but then thought that its too much for road use.

Upper one im just replacing with a new one and lower one im upgrading from rubber bushing to the balljoint like the upper one already is. On e46 m3 or e85 z4m they are both balljoints stock.

Hard to find these Hardrace trailing arm bushings and limiters in EU. Hardrace has their own EU website but those bushings were not in stock and had a 3week shipping time
Finally found 1 set in stock at Atomic-shop located basically next to Nürburgring. And RTAB limiters i could not find anywhere in EU so ordered them from USA (FCPEuro)...

I still have a few things to order/arrive ... im also replacing front strut mounts and spring pads and front wheelbearings. Can probably take my Z to the shop for install in a week or 2.

Where did you get those chunkier mounting plates/carriers?
Im planning on using stock ones atm.. What is the benefit?

On the Hardrace RTAB-s and limiters theres a great video on youtube btw:

[B21]

Yes saw the video a while back, in part that’s why I went down the Hardrace route.

I did buy the RTAB limiters too, but the design of the new RTAB cage means there’s no room to slot the RTAB limiters in..

It’s flat internally rather than curved and the steel is much thicker..

https://www.ebay.co.uk/itm/224902388...mis&media=COPY

It’s a German company that makes these chunky brackets..

[KennyP]

So these epytec carriers have limiters already built into their design, eliminating the need for them.

Thanks for the link.
I think i can get them even cheaper from Epytec homepage... shows 89 eur + shipping on there. No ebay tax .

I havent had any issues with alignment yet, and i do go to alignment fairly regularly.
Do you run your own custom alignment setup?
Years ago when i owned a 2004 ep3 Civic Type R, with those it was popular to change alignment settings to a so-called "fast-road setup" that reduced understeer and gave better turnin..
On e89 z4 i havent played around with alignment settings except having more camber at the front due to m3 arms...other than that i set my car up to stock specs...

I did bookmark these carreirs in case we run into alignment issues this time. If i do ill get a set of these aswell.

TBH had i known about these carriers earlier i would have bought them instead of those limiters. i paid like 60 eur for the limiters because of all the shipping across the pond and import tax.... 89 + some shipping within eu isnt a big stretch from there.

[B21]

I’ve got adjustable camber / castor plates on the front..with adjustable rear camber arms on the rear..

I’m running about 7 degrees of castor for more stability (5 stock)..about 1.7 degrees camber front (stock 0.50 for more turn in / less understeer.

Stock front toe in

Rear camber is 2 degrees which is stock , tried more but it was counter productive..rear toe in is with limits but could a bit more to get to factory perfect set up hence the adjustable toe in plates..

I’ll dig out the last adjustment table which was pretty good for ‘hooning’ on my favourite roads here is Scotland.

[B21]

Originally Posted by KennyP

So these epytec carriers have limiters already built into their design, eliminating the need for them.

Thanks for the link.
I think i can get them even cheaper from Epytec homepage... shows 89 eur + shipping on there. No ebay tax .

I havent had any issues with alignment yet, and i do go to alignment fairly regularly.
Do you run your own custom alignment setup?
Years ago when i owned a 2004 ep3 Civic Type R, with those it was popular to change alignment settings to a so-called "fast-road setup" that reduced understeer and gave better turnin..
On e89 z4 i havent played around with alignment settings except having more camber at the front due to m3 arms...other than that i set my car up to stock specs...

I did bookmark these carreirs in case we run into alignment issues this time. If i do ill get a set of these aswell.

TBH had i known about these carriers earlier i would have bought them instead of those limiters. i paid like 60 eur for the limiters because of all the shipping across the pond and import tax.... 89 + some shipping within eu isnt a big stretch from there.

Here are the settings from last alignment as promised...

First attempt and then final settings.. rear camber was increased..

[B21]

Final settings (pre adjustable toe plates)