A small amount that's penned about part of tyre (5)
I believe the answer is:
tread
'part of tyre' is the definition.
('tread' is part of 'tyre')
'a small amount that's penned' is the wordplay.
'a small amount' suggests taking the first letters (I've seen 'smallest amount of' mean this).
'penned' becomes 'read' (I am not sure about this - if you are sure you should believe this answer much more).
The initial letter of 'that' is 't'.
't'+'read'='TREAD'
'about' acts as a link.
Can you help me to learn more?
(Other definitions for tread that I've seen before include "Put one's foot down!" , "Sole of a shoe" , "dance" , "Step (heavily)" , "Depth of grooving in a tyre" .)