When you’re fishing with crankbait lures, you actually want contact with the bottom of the lake or river that you are fishing in. For this reason, you want a crankbait that can reach that depth at least, with a few feet of extra wiggle room to account for variances in the lakebed surface.
A good fish finder will be able to tell you how deep the area you are in is, or you can do some research online about the body of water you will be in and find out about how deep you will be aiming to go.