I am looking to lower my new E34 (5 Series BMW) I have 18's on it and I have been told that you can't lower it unless I put 17's on. Does anyone know or can anyone help?

It depends on how low you want to go.

If you dont go silly shouldnt be a problem.

My mates old m5 E34 was dropped by 40mm on SCHNITZER 18" running 245/40/18. thats 8.5 J X 18" i will ask him nextime i see him if he did any arch work but i dont think he did.

He did you a full suspension kit though not just springs.

dont go more than 40mm,get a full kit (srpings and dampers) and take it to sprayforce and if u need archwork im sure they can do it for a reasonable price