2020 4Runner limited

I have a 2020 4Runner limited it has 20” rims on 245/60R20 tires I want to put on some 18” rims what is the biggest tires size I would be able to have stock without needing lift or cutting anything and would -18 offset be okay? Thanks for any help!

 

They are less good tires in 18” than 17”. 275/70R17 is the biggest you can fit with no offset and no trimming.

 

I don't know about the offset you should convert it to backspace measurement, and compare with the listed measurements on the image, or find the stock specs for the 7.5" wide stock wheels, and check that your wheels are close to the stock offsets.

Chart from here
https://www.4runners.com/threads/at-tire-shopping.26750/#post-366446