Uprated rear trailing arm bushes, adjustable toe in plates and rear linkage bushes

[B21]

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..

 

[Marcoose]

What is the goal you’re trying to achieve ?

 

[B21]

What is the goal you’re trying to achieve ?

As stated, 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..

 

[flybobbie]

I read somewhere increasing rear camber increases toe in.
So does the vehicle squat and go more toe in under acceleration.
Thought that might increase stability.

 

[B21]

I read somewhere increasing rear camber increases toe in.
So does the vehicle squat and go more toe in under acceleration.
Thought that might increase stability.

Yes rear camber and rear toe in are interrelated through the design of the suspension.

The problems are that for many cars (my two E89s) it’s difficult to get the camber you want AND the toe in, especially matched toe in on both sides.

The adjustable retainers for the RTAB and the rear trailing arm help that by decoupling camber and toe in.

The problem is that under power the RTABs distort and toe can move from toe in to toe out causing an unpredictable and difficult rear steering effect that dramatically reduces stability..

Age, wear and increased power exacerbates this condition..hence a variety of techniques are used to address it, RTAB limiters. , roller bearings, polyurethane bushes.

 

[Marcoose]

The more power, the more aggressively applied the worse the problem

Honest question: you feel this at street speeds ?

I drive spiritedly for my age and local road conditions. And I'm a notorious late-braker who's gingerly back on power before the apex, and, often never totally close the throttle. I don't remember feeling the rear steering on its own. I need to pay closer attention to that.

I wonder if there's a bit of driving style in the equation.

 

[B21]

The more power, the more aggressively applied the worse the problem

Honest question: you feel this at street speeds ?

I drive spiritedly for my age and local road conditions. And I'm a notorious late-braker who's gingerly back on power before the apex, and, often never totally close the throttle. I don't remember feeling the rear steering on its own. I need to pay closer attention to that.

I wonder if there's a bit of driving style in the equation.

Several different points..

Many people just accept the limitations in the stock (deteriorating) chassis because they either are not bothered, the issues don’t manifest themselves in their type of driving, they are happy to add the extra skill / effort to compensate or they are aware of ‘issues’ but haven’t a comprehension of what factors are causing said issues.

Where, when, how and who with you are driving makes a huge difference.

I drive in many areas where unusually speed limits are not a limiting factor…you can go as fast as you wish to do so.

I drive in all weathers as many of my trips are booked weeks or months in advance, so I need to be comfortable in all sorts of weather conditions, the joke being in Scotland that we have at least 4 seasons in one day…so drivability in damp, wet conditions are keep factors.

I drive often in the company of some drivers whose driving style at times is definitely fast n furious, I like to be able to keep up with them taking into account our different driving techniques.

The roads I drive on are often, usually bumpy, with mix surfaces, lots of potholes, patched and other wise.

From a driving style taking those factors into consideration I ease up on the throttle well in advance of a corner, I enter the corner on a trailing throttle with my foot ready or covering the brakes…when I reach the apex I feed the power in gently and then as the corner straightened out I apply as much throttle as required..upto 100% if I’m ‘hooning’ and any people I’m driving with are happy with that style.

If I’m following others I never simply follow them, whether that’s on straight parts and especially in corners. I’m always very mindful of possible issues around corners (tractors, sheep, deer, camper vans, grockles, cattle or logging lorries)…

I never corner to the limit of the car intentionally for all those traffic and road surface reasons.

I’ve never enjoyed the experience of poor or indifferent handling, whether that’s the 30+ cars, 20+ motorcycles or 10+ aircraft.

So if I can ‘improve’ the handling to suit my tastes then why not.

I’m fortunate in having the time, money and inclination to read, assimilate, try, test, iterate my chosen strategies…

FWIW I lived and worked In California for about 10 years from 1997-2007 and spent a lot of time driving the whole state..I’d say that the driving style and requirements there are very different to those of my home country.

Hope that helps..

 

[Argyll Andy]

I drive in many areas where unusually speed limits are not a limiting factor…you can go as fast as you wish to do so.

I drive often in the company of some drivers whose driving style at times is definitely fast n furious

That made me LOL :rofl: :rofl:

We should get Visit Scotland to incorporate that into their literature

 

[B21]

I drive in many areas where unusually speed limits are not a limiting factor…you can go as fast as you wish to do so.

I drive often in the company of some drivers whose driving style at times is definitely fast n furious

That made me LOL :rofl: :rofl:

We should get Visit Scotland to incorporate that into their literature

I was trying to be tactful :rofl: :rofl: :rofl:

I did say ‘some drivers’ and ‘at times’…. :tumbleweed: :driving:

 

[Marcoose]

Indeed, there are significant differences between Scottish and Californian roads. But there are many places here where you can, and some do, go as fast as their hearts desire. And then the solo crashes, the RIP threads, and the ‘Celebration Of Life’ gatherings. I’ve been here for only 14 years, and yet attended 20+ of these gatherings. The local saying is ‘when speed exceeds talent’.

I like my vehicles sharp, but I leave the fast and furious for the track.

I’ll save this thread for if and when rear steering start to appear and become unsafe.