Great Britain's Shanaze Reade is seeded fifth in the BMX after posting a time of 39.368 in the seeding run time trial.
Reade was the first rider to go under 40 seconds but was then pushed down the standings.
Four years ago Reade was tipped for gold but missed out after crashing in the final. She is among the favourites to get a medal in London.
Australia's Caroline Buchanan set the quickest time in the seedings.
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