Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the largest grid with a Driver of ralph firman, and a Lap smaller than 18?

### Inputs:
table_name: table, columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']

### Response:
SELECT MAX Grid FROM table WHERE Driver = ralph firman AND Laps < 18