The vantage S wheels requirement is 245/40ZR19 and 285/35ZR19

Is it possible to install 235/40ZR19 and 275/35ZR19 tires instead on the V spoke vantage S wheels?

These are the wheels:

 

Why would you want to go narrower? If anything you could go up a size to 255/35/18 & 295/35/19

 

Just curious if they will fit or if there will be any issues with putting a smaller tire.

 

no issues with smaller tires, the only concern being that the tire will stretch more so it will look uglier and the outter edge of the rim will be more exposed to hitting something when you drive over a pothole etc. Also smaller tires might make your speedo appear slightly quicker.

 

Agreed, it won't look as good and the risk of scraping/curbing your wheels increases significantly. You can run a wider tire 245/285 setup (which would be like a 255/295 setup). Example, Michelin PSS tend to run one size wider than pirellis and continentals etc so you have to add a size to the actual number it states.