You shouldn't have any issues running 20s and wont need to change anything else. Just make sure you get the right offset and load compliance from the wheels and tyres. Check out the FAQ up the top of this forum section. Theoretically you can void some parts of the warranty concerning the suspension if you change, but it depends on who you talk to at Toyota as to if you get covered if something goes wrong. thanks matey...will look into things a bit more