Is it ok to put 285/55/20 tyres on the front same as the back instead of 255/35/20s???

tyre rotation is from front to back on the same side of the vehicle . It is recommended by tyre shops as it is good for business ( 4 tyres instead of 2) The other down side to tyre rotation is that you do not get a good idea of wheel alignment problems to know what to fix. Next down side is that once a wear pattern has been established that pattern will continue because the tyres are radial construction
Front drive cars wear out the front tyres in 1/4 the time that it takes for back tyres and a faulty tyre will have a wear pattern that indicates wheel alignment/ driver abuse but in fact is from case construction.It is something that I have not recommended since radial tyres came into being.

take the car to a suspension specialist shop and have the rear wheels aligned first
have the suspension checked for worn mounts or bad springs
it is very important that the rear end is aligned before the front end
suspect that the suspension rubbers need replacing as it is over 6 years old
the tyre rotation is a myth perpetrated on drivers to sell tyres
when the tyre construction was cross-ply and not radials yes rotation then on cross-ply tyres could get the wear to even out but with radials once the wear is started then the tyre continually wears in that pattern regardless of which wheel it is on
even if you take that tyre of the car and put it on a trailer , it will still continue to wear in that pattern
tyres are no longer rotated but simply put front to back on the same side other wise the belts flex in a new direction in the tread and fail earlier that expected
besides that fact that tyre rotation will not allow you to monitor for suspension problems or wheel alignment problems and cost you 4 tyres at a time instead of two

That would more then likely fix your problem. A tire may be seperating ,I would replace the front two. ok, Good luck to ya.

replacing one is ok but replace two minimum to create even wear on the tires

check tyres for wear-wheel balance needed if visibly ok-have a wheel alignment after a tyre rotation-best even tyres to be put on fronts-they will carry out a safety check all suspension and steering before doing the wheel alignment

Yes it is, you wont notice any differens except the "look", your car wont look so cool as whit the 275 tires.

40's profile are a little lower. That will not affect your car in ant way.

you need to inspect your front tyres for damages, you can start by changing front tyres with back, and test drive, if tyres look ok then have tyres balanced.

32 psi in the front and 30 psi in the back. if the tyre preasure monitoring is acting up even with the preasures ok. take the car to a renault garage to have them re initialised

18" 225/40's on the front and 18" 255/35's on the rear