Radial on a Rolls (4)
I believe the answer is:
tyre
'radial on a rolls' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tyre that I've seen before include "Rubber wheel; port" , "A circular cushion" , "Band on wheel" , "Rubber covering on a wheel" , "Old Phoenician port" .)