What are RTABS
This article will focus on the E36 and E46 rear suspensions. Rear trailing arm bushings or RTABs are used in conjunction with a mounting bracket to connect the vehicle's rear trailing arm to the chassis and provide adjustment for rear toe geometry. This is done via the bracket which has slotted holes that allow the trailing to be moved either in towards the center of the vehicle or out away from the center of the vehicle to ensure the vehicle is tracking straight on the road. Generally, all E36s and E46s run a slight amount of toe-in in the rear. This provides forward stability as you drive along. Figures 1 and 2 below indicate where they are installed on either chassis.
Why do I need offset trailing arm bushings?
While the standard centered trailing arm bushing is fine for the stock E36 or E46. For those who have lowered their vehicle significantly or added a large amount of negative camber, this may not be the case. When lowering an E36 or E46 this will inherently add camber. Alongside the increased camber will also come increased rear toe-in and for those who are increasing rear camber, further, this effect will be even more noticeable. Eventually, the stock trailing arm brackets will reach maximum adjustment and the vehicle will no longer be able to be aligned to the desired spec for optimal tire wear or performance. This also applies to those with drift cars who are trying to pull as much camber as possible out of their vehicle in order to grip their car up as much as possible. If this is the case they will see the opposite effect. The vehicle will begin to toe out and with the factory adjustment brackets, proper alignment may no longer be possible. This is where the Garagistic offset RTAB comes to the rescue.
How the Garagistic Offset RTABs work
The Garagistic Offset RTABs can be used in two ways, to correct excessive rear toe in or to correct excessive rear toe out. Depending on your application and goals, these bushings will allow you to correct your vehicles toe to an extent and help bring any unwanted toe in-or-out back closer to the factory or desired setting. For drifters, these can also be used to increase rear toe in if your goal is to grip the car up as much as possible. The Garagistic Offset RTABs are designed to move the trailing arm inside the bracket either in or out from its original position. This is done by adding material to one side of the bushing and removing material from the other. (See below picture)
Standard E36/E46 RTAB
Offset E36/E46 RTAB
Installing your Garagistic E36/E46 Offset RTABs
First, you will need to determine what your vehicle needs in order to align it as desired. To do so we recommend having an alignment check done by a professional, or if you are a DIYer, use toe plates to determine where your toe is currently sitting.
If your vehicle has an excessive rear toe-in you will need to move the trailing arm back out away from the center of your vehicle. This means that you will need to install the offset trailing arm bushing with the thinner side on the outside of the trailing arm closest to the outside of the car and the thicker side of the bushing on the inside of the vehicle closer to the drivetrain.
If your vehicle has excessive rear toe out or you are looking to increase rear toe-in you will need to move the trailing arm in towards the center of the car. This can be done by installing the offset bushing with the thinner end on the inside of the trailing arm towards the center of the vehicle and the thicker end of the bushing on the outside of the trailing arm towards the body.
After you have installed your offset trailing arm bushings you should be able to bring your alignment mostly into factory spec or to your desired setting. However, here is a list of common faults that can occur after installation.
My alignment is now further out than it was originally.
In this case, it is most likely that you have installed your bushings backwards. To remedy this simply reverse the installation and re-check.
One side of my vehicle aligns properly however the other is still out.
In this case, it is most likely that something in your suspension is bent. This is most common on E46s as they have aluminum upper control arms which over time and in harsh driving conditions can bend and cause toe issues. These bends may not be visible to the naked eye. Most likely you will have to replace components one at a time and recheck alignment until it's brought back into spec.
I have installed my offset RTABs but I still can't achieve the desired toe setting
If you're running into this issue most likely you are pushing the physical limits of the rear suspension by either running your vehicle too low and with too much negative camber or running too high of a ride height with too little or even positive camber. The only option (while still using factory suspension components) from here is to modify the existing trailing arm brackets to allow more actual adjustment within the RTAB pocket.