Lightweight motorcycles (6)
I believe the answer is:
mopeds
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lightweight motorcycles</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mopeds that I've seen before include "Light motor cycles" , "Lightweight motorcycles" , "Low-powered motorbike" , "Low-powered motor-cycles" , "Low-powered motorbikes" .)