H e y I have a 2021 is300 fsport with
235 40 19 and 265 35 19 tyres
I'm looking at getting some Michelin pilot sport 4s tyres,
car is stock height

Question could i go up a size in tyres?
or is it not worth the size change?
Also will a bigger tyres fit?

 

Welcome. Is there any reason in particular you want to go up in size? You'd be safest just sticking with the original sizing to avoid damage to the AWD system. If you go up in size, the ratio of tire circumference front-to-back has to be extremely similar to original.

 

I was thinking about the same - I know that diameter of the tires has to be very very close to stock, but what about width? If i put 10-20mm wider tires while keeping same diameter, would it affect AWD system negatively?

 

It would not.