Expandable shower curtain rods, also referred to as tension rods, make it easy to get a perfect fit. This type of rod contains springs that expand or shorten it, depending on which way you twist the rod. Most expandable rods have an adjustment range of 12 inches. For example, you might purchase a tension rod that covers 24 to 36 inches, depending on the width of your shower.
Put your shower curtain on the rod and push it to one side.
Hold the expandable shower curtain rod up to the shower walls. Note whether the rod is too long or too short.
Twist the rod counter-clockwise in the middle, where the two rod sections meet, to lengthen it if it's too short. Twist until the rod fits snugly between the shower walls.
Twist the expandable shower rod clockwise to shorten it, if it's too long. Twist until the rod fits snugly between the shower walls.