CREATE TABLE table_54750 ("Rider" TEXT, "Manufacturer" TEXT, "Laps" FLOAT, "Time/Retired" TEXT, "Grid" FLOAT)

What is the grid for dirk heidolf?
SELECT SUM("Grid") FROM table_54750 WHERE "Rider" = 'dirk heidolf'
SELECT SUM("Grid") FROM "table_54750" WHERE "Rider" = 'dirk heidolf'