CREATE TABLE table_name_78 (laps INTEGER, grid VARCHAR(255), bike VARCHAR(255), rider VARCHAR(255))
What is the highest Laps, when Bike is "Yamaha YZF-R1", when Rider is "David Checa", and when Grid is greater than 18?
    
SQL: SELECT MAX(laps) FROM table_name_78 WHERE bike = "yamaha yzf-r1" AND rider = "david checa" AND grid > 18