255/45/18 on 9.5j rims on e39

Guys

I need some help. I inherited a set of 255/45/18 Michelin tyres and would like to fit them on my Alpina reps at the rear. The rims are 9.5j. Normally these will take a 265/35/18. What effect will the 255/45/18's have on the suspension, traction and speedo, brakes? Is it dangerous to fit these tyres on my e39. Any advise will be appreciated. Need to know if I'm going to compromise safety with this setup.


Thanks