Possible Clues:

• 'There's no tradition of bears on --s here' (John Irving, The World According to Garp)
• Circus clown's transport?
• Balancing act woman president will reportedly provide
• One-wheeled bike used by acrobats
• One-wheeler
• Likely to cause a slip, relative coming round - on one of these?
• Not good conditions for driving in relation to this from of transport?
• Thing requiring a balancing act
• It only requires one to ride
• On which one may ride round Oxford, say, first?