[tadaska]

I've ordered a set of M3 front axle control arms (upper and lower) to replace the stock ones my car has now. I thought I had to get an M3 headlight level regulating rod too, but then I started thinking... my car's suspension will remain at stock height (no lowering) and the M3's suspension is lowered. Now, I don't understand all the geometry involved but wouldn't an M3 rod on full height car make light level wrong? And since my stock arms are different from the M3 arms I'm guessing using the same leveling rod I have now would not work either.



Which one do I need?

[djh2]

The M3 control arms are a different shape than the stock ones. You need the M3 headlight level rod. The control arms will push out the wheels slightly, so you'll need an alignment afterward.

I made this swap on my 328i, and it works as expected. My understanding is that ride height is more of a function of shock/spring than control arms. The control arms set the wheel geometry throughout the suspension travel (camber, caster etc.).