The Graco transformer systemajig fits in the back of my dad's 325is, but BARELY. The thing can't move at all, and that's with just enough legroom for the front passenger if they are >6'.

Oh, and another thought. Although I may get shit for this from the safety freaks on the board, you could always just put the thing in the front passenger seat. No airbag to stop you. The seats are quite narrow on the other hand...:banghead:

Britax does fit. Legroom is tight if you have a large passenger, but not a problem if you have the freedom to slide the seat up a little. There's a bit more lateral play than in an E46. Funny enough but getting in and out of the E30 coupe is actually easier for a toddler than with an E46 sedan... the folding action of the front seat provides plenty of access room.

LMK if you have more specific questions.

kurt