Trailing arm re-inforcement.

[Jean]

So I did search on this and didn't see much on it. So, I want to properly re-inforce the trailing arms and sub-frames.

Have anybody done any testing or measurement on the best route to take here? Basically should I just use an m-coupe trailing arm as a reference?

Thanks

[PiercedE30]

I would use the m-coupe TA as a reference. Just be very careful when doing the welding. It is VERY easy to warp the arms and screw up the whole shebang. I would take a look at the DTM trailing arms and use those as reference as well.

[jlevie]

Why would you think that is necessary? We can't modify the trailing arms on a Spec E30 other than reinforcing the sway bar link pick up points and we don't see any problems with the trailing arms.

[Aptyp]

the only reinforcement i can think of is the sway bar link. Most people, even in spec. e30, run with rear sway bar off.

Urethane mounts and bushings is what you should do to tighten the rear.

[BeirBrennerE30]

the e30 trailing arms have a lot of flex in them. BMW knew this and when they added more power to that rear suspension they reinforced the arms in the mcoupe.

Best place to start is adding reinforcement bewteen the 2 mounts creating an A type shape.(a la mcoupe) also good is to add 2 more reinforcements to the hub area. One to support the hub from going side to side(toe change) and anther to reinfor the top to bottom movement(camber change) its kinda hard to describe and I didnt take pics when I did mine... sorry. Once you get the arms out you should see what you can do there. Also as otehrs have said reinforce the sway-bar mount at the same time and becareful not to warp anything or your be worse off than when you started.

[BeirBrennerE30]

oh yeah... and pics of group A e30 M3's are your freind

[Jean]

jlevie - this isn't for spec e30, and spec e30 isn't really pushing the suspension to it's limits with bilstein sports and h&r race combo imho.

Aptyp - or poly/aluminum in subframe and spherical or rubber in trailing arm. the trailing arm location moving points are multi-axis, so in theory you don't want to use urethane or poly there as with time it would work itself out to have more play than it did originally. rubber presents binding at the limit, but atleast it goes back to it's original shape. spherical bearings would be best, as the loud from the initial movement to it's max movement is the same, tension wise.

the e30 trailing arms have a lot of flex in them. BMW knew this and when they added more power to that rear suspension they reinforced the arms in the mcoupe.

Best place to start is adding reinforcement bewteen the 2 mounts creating an A type shape.(a la mcoupe) also good is to add 2 more reinforcements to the hub area. One to support the hub from going side to side(toe change) and anther to reinfor the top to bottom movement(camber change) its kinda hard to describe and I didnt take pics when I did mine... sorry. Once you get the arms out you should see what you can do there. Also as otehrs have said reinforce the sway-bar mount at the same time and becareful not to warp anything or your be worse off than when you started.

That's where I would like more info, on the toe change reinforcement and camber change. I have the arms out already, these are for my track car and I want to get them re-inforced at the same time with sub-frames.

[kenika65]

Im subscribed, cant wait to see some pics

[Jean]

Does anybody have a set of oem re-inforced arms, I wouldn't mind knowing exact measurement on the location of the horizontal support bar. I want it to be as close to oem as possible

[BeirBrennerE30]

closer to the mounts the better

[AndrewG]

Well, it took me a while to figure out which site it was that had all the exact info you want but I found it. ....unfortunately it looks like the site shut down or something. I knew I should have made a site copy when I found it a few years ago...

This was the link and it had lots of diagrams as well.

http://www.e30m3performance.com/tech_articles/susp-tech/gr-a_arm/index.htm

If you search google you can at least read it by using the google cache but that site had tons of other technical info. I'm hoping it's just temporarily down.

[BeirBrennerE30]

this is how you add strength to the arms front a rear...

[Jean]

AndrewG, bummer, I've seen articles on that site and they were good, maybe it will come back up soon.


BeirBrennerE30 - do you have any information on these? reason for the inner point being stock unlike the outer mounting points on the trailing arms for example. I just emailed this picture to a friend of mine running in SM to check if this would be legal in the class I a race in. Where did you find these or are these yours?

[PiercedE30]

The pictures are from S14.net. A guy in the UK, I believe, is modifying them. He charges like 2000 for the rears and another 1000 for the fronts. It is under the "Ultimate trailing arm" thread.

[AndrewG]

AndrewG, bummer, I've seen articles on that site and they were good, maybe it will come back up soon.


BeirBrennerE30 - do you have any information on these? reason for the inner point being stock unlike the outer mounting points on the trailing arms for example. I just emailed this picture to a friend of mine running in SM to check if this would be legal in the class I a race in. Where did you find these or are these yours?

Hah, if that site was up it would explain the reason quite well. :(

They put those there on the the GrpA e30 M3s I think. It was there to screw in or out to adjust toe easily. The other side is left alone I think because they didn't have much of a reason to change it and if they had a big eccentric in there maybe it would be easier to adjust camber than an eyeball type mount?