If you dimension a closed-profile sketch that would cause an over defined sketch, the dimension is automatically changed to driven. When you sketch the last entity to create a closed-profile sketch, it may clash with inferred relations from the other sketch entities.

What does make this dimension driven in Solidworks mean?

Make This Dimension Driven. The over defined or unsolvable state is repaired. Leave This Dimension Driving. The sketch remains over defined or unsolvable. Look for other dimensions or relations that you can delete or change.

What are driving dimensions?

The driving dimensions are the values that were directly input into BikeCAD. For example, head angle and seat angle can be directly specified through text fields in BikeCAD. The driven dimensions are calculated by BikeCAD. Driven dimensions will change as a result of changes to driving dimensions.