What is the highest tire size you can put on a 2001 Alero to gain more clearance?

The highest tire size that you can put on a 2001 Alero to gain more clearance would depend on the stock tire size that the vehicle came with.

With the stock tire size of 215/65 R16, you could install a tire size of 225/60 R16. This will increase the diameter of the tire by about 1.2 inches, which should provide you with some additional ground clearance.

Please note that increasing the tire size may affect the handling and performance of the vehicle, so it's always best to consult with a professional before making any changes.