a rule of thumb is 4" either way of tire to rim.....
you can easily put a 13.5 on an 8" rim without much issue.....
when i worked @ wheelworks... there was a customer that brought in a lifted first gen toy pickup... he had the stock 15x6 chrome wheels.... we put 33x12.5s on it....... other than probably some irregular tread wear on the street because of the contact patch, there were no safety or driveability issues with it
