Tires: replacement tire/wheel

Question
can I replace original tire/wheel 205x55x15 by 205x40x16 without compromising safety?

Answer
Gil,

No, you would be compromising safety.  The load carrying capacity would be less and that leads to tire failures.  Very bad.

May I suggest you look up your vehicle on Tire Rack and find what tire size they say will work - both in terms of load carrying capacity AND physical space under the fenders.