Page 126 - Annual Training Class 4_7 classroom 20-21
P. 126
Tyre tread depth
In simple terms, grooves containing tread wear indicators
(TWI) or grooves cut as deep as those containing the wear
indicators when new, are considered to be primary grooves.
Other grooves or sipes that aren't cut as deep as the primary
grooves are secondary grooves and aren't to be considered
when assessing tread depth.
