user: Question: Which Rider finished with a speed of 81.91mph?
Columns: ['Rank', 'Rider', 'Team', 'Speed', 'Time']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Georg Auerbacher /H.Hahn', 'BMW', '86.86mph', '1.18.12.0']
SQL:

assistant: SELECT "Rider" FROM "Table" WHERE "Speed" = '81.91mph';