if the tires are bad internally a high road force would show on the display.
depending on who you ask, anything above 10-15 is bad or 25 is bad. pick your poison. i think the industry standard is anything above 25 is considered a bad tire internally.
thats what i have read, so ymmv
when i had new wheels/tires put on the 26 4R, i think the highest was 18 and the others we in the single digits.