Technician's beginning to study surface of tyre (5)
I believe the answer is:
tread
'surface of tyre' is the definition.
(tread can mean the surface around a tyre)
'technician's beginning to study' is the wordplay.
'beginning to' suggests taking the first letters.
'study' becomes 'read' (synonyms).
The first letter of 'technicians' is 't'.
't'+'read'='TREAD'
(Other definitions for tread that I've seen before include "Gripping part of tyre" , "Step (heavily)" , "Depth of grooving in a tyre" , "Surface of car tyre" , "Tyre moulding" .)