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M-Coupe Rear Trailing Arms

The M-Coupe rear trailing arm compared to the standard E30 unit Pictures and part numbers supplied my Mike Krnc.

It is fairly well known at this point that BMW's M-Roadster and M-Coupe cars were designed with a rear suspension that is very similar to that of the earlier E30 series cars. This includes the E30 M3 of course. That is the reason that the very popular M-Coupe rear differential cover bolts right on to an E30 M3.

However, it is becoming apparent that the M-Coupe suspension is not just similar to that on the E30 chassis, but is actually identical in many respects, such as angles and pick-up points. In fact is is possible that the M-Coupe / M-Roadster rear subframe and trailing arms may be a bolt on replacement for the standard E30 units. The only difference being the "ears" for the caliper mounts and the various brackets and fittings.

The M-Coupe rear trailing arm with the One of the main differences between the M-Coupe rear trailing arms and the earlier E30 arms is the factory addition of an "A-arm" type fortification between the two "legs" of the trailing arm. This was presumably done to strengthen the trailing arms so that they could cope with the much higher torque output of the U.S. and Euro spec M-Roadsters and M-Coupes. It is said that these U-shaped brackets are available separately from BMW dealers but I do not know the part numbers (this turns out to be false, they are not separately available - sorry). In any case, a look at these pictures shows that the brackets would be very easy to duplicate by any competent welding shop. In fact, a rectangular tube would function even better than this U-shaped channel, and would be easier to source. Make sure your welding shop knows how to weld a steel structure in such a way that the heat from the welding does not warp the part.

The M-Coupe rear trailing arm with 'camber-gusset'

The red arrow in the photo above shows what I refer to as the M-Coupe "camber gusset". It is a separate fortification from the "A-arm" gusset/bracket. It is obvious from observation that this gusset was added to prevent high cornering loads from flexing the trailing arm and allowing the camber setting to change i.e. dynamic camber.

This camber gusset may also be available separately from BMW dealers (Ed. note: it's not). But as with the A-arm gusset, it is apparent that any welding or sheet metal shop should be able to duplicate this gusset with a minimum amount of effort.

Close-up of the M-Coupe rear trailing arm with 'camber-gusset' Those in the mood to experiment might be interested in the following part numbers:

M Coupe subframe ($491 list)

p/n 33 31 2 228 200

M Coupe subframe bushings (~$20 ea.)

p/n 33 31 1 090 946

M Coupe trailing-arm bushings (~$40 per pair)

p/n 33 32 9 058 822

M Coupe trailing-arms (~$300 ea.)

p/n 33 32 2 227 967 lt

p/n 33 32 2 227 968 rt

Ed Note: I have discovered that the M Coupe subframe bushings will NOT fit the E30 chassis. They are too short. However, the M Coupe subframe itself may well fit our cars. The jury is still out on that one. The M Coupe trailing arm bushings WILL work on the E30 chassis - I did that. It should be noted that the p/n given above is for the eccentric trailing arm bushings, which can be used to effect about a 0.5 camber change to the rear wheels. The Parts CD shows that the p/n's for the M Coupe eccentric and regular trailing arm bushings are the same as those for the E30 chassis. So no increase in rubber durometer will be realized. Too bad 8^(

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