Travelling at 100 mph (3-2)
I believe the answer is:
ton-up
'travelling at 100 mph' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ton-up that I've seen before include "Travelling at one hundred mph" , "Going at 100 mph" , "Travelling at 100 mph" , "Fond of travelling at high speed" , "going quickly" .)