MultiLink Rear Subframe retrofit

[HCMW Adam]

Do it! Any e30 rear end is going to need full refresh, so there is some work traded. I think a rear tube structure grafted into the e30 structure would be pretty do-able.


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[LJ851]

Any suspension, no matter how poorly designed, can be made to work reasonably well if you just stop it from moving.

-Colin Chapman

[nrubenstein]

The advantages of multi link are likely less unsprung weight and better toe/camber control during suspension movement.

In the DTM cars they got around this but building stronger lighter trailing arms to reduce weight and decreasing the sweep angle of the trailing arm 3degrees and then use stiff springs in the rear to reduce movement. That toe change with wheel movement is what gives the e30 its back end movement that makes it fun to drive. Multilink is definitely better in terms of performance (as long as all the link mounts are in the correct spots to take advantage of it) but would change the cars character.

It’s also worth noting that that the semi-trailing arm suspensions weren’t *that* terrible. In fact, they built a bunch of racing E36es with the E30 rear axles. (And I’m not talking about racing compacts, but regular E36es.)

[BeirBrennerE30]

The advantages of multi link are likely less unsprung weight and better toe/camber control during suspension movement.

In the DTM cars they got around this but building stronger lighter trailing arms to reduce weight and decreasing the sweep angle of the trailing arm 3degrees and then use stiff springs in the rear to reduce movement. That toe change with wheel movement is what gives the e30 its back end movement that makes it fun to drive. Multilink is definitely better in terms of performance (as long as all the link mounts are in the correct spots to take advantage of it) but would change the cars character.

[cwlo]

Well I appreciate the collective advice. Its always nice to get a 2nd opinion on something that can't be undone very easily.



Any others want to chime in?

[JimmyP]

Mike Akard has already done a version of this with E36 parts, as has a shop in the mid atlantic (I think NC area).
As you have noted you basically need to back half the car to do it. At that point just built a tube frame car and drop an E30 body over top.
Lots of work for a unknown payoff.

Im the last person to say dont do any stupid fabrication project, I've done my fair share, but do it with a return in mind (lower consumable costs, a target of lap time reduction, weight reduction, better parts / service availability, etc).

As cool as I think it might be to achieve, Im having a hard time seeing the effort / $ / return ratio on this project unless you have a target in mind other than "because its there".

[nrubenstein]

I guess that is the question with this swap, as it hasn't been done before other than once or twice, and there's no feedback on its results. I don't mind blazing a trail, as I enjoy the fab work, but I don't want to mess up the car either.



What exactly about the multi-link will make it a negative over the stock suspension?

Multilink is boring. E30s have no problem putting down power.

[cwlo]

I guess that is the question with this swap, as it hasn't been done before other than once or twice, and there's no feedback on its results. I don't mind blazing a trail, as I enjoy the fab work, but I don't want to mess up the car either.



What exactly about the multi-link will make it a negative over the stock suspension?

[nrubenstein]

I don't mean to be a downer, but why go through with this? A lot of the character of an E30 is the non-independent rear end.

If you want a light car with independent rear suspension, why not get an E36?

Agreed. It's a ton of effort to make the car drive worse.

[ForcedFirebird]

Sub'd for pics.

I don't mean to be a downer, but why go through with this? A lot of the character of an E30 is the non-independent rear end.

If you want a light car with independent rear suspension, why not get an E36?

The e30 has independent, it's just semi-trailing arms, not milti-link. ;)

[earthwormjim]

I don't mean to be a downer, but why go through with this? A lot of the character of an E30 is the non-independent rear end.

If you want a light car with independent rear suspension, why not get an E36?

[cwlo]

So I have done a bit of research, and am seriously considering retro-fitting the e82/e90 rear multi-link into the e30. Seems like a great way to eliminate the inherent flaws of the stock rear suspension in one swoop. That said, it does involve quite a bit of fabrication, so its probably not the best or recommended route on a $$ or time basis. But hey, hobby time is different!


This has been already done on the Piper motorsport Franken M3, so the route has been charted, and I will probably follow that. I do have a complete rear clip from an e90, so grafting that in is one option, but it is a bit more complicated, in that the e90 uses high strength steel in different places, which makes welding it a bit more complicated, not to mention the differing steel that would be present which might introduce other problems.


So, seems the best route as of now is to remove the inner wheelwells, and nearby frame, and then weld in a fabricated frame from 3" square tube that the e90 subframe will bolt to. The one downside I see is the rear track width will be increased approx 2.0", necessitating flares. Also probably a good chance the rear seat will no longer fit.



Anyway, I will post up some pics when I get a chance, and am open to any comments. I currently have the existing rear subframe and gas tank removed, but have not cut out the frame yet, as that is a point of no easy return.