I changed my rear, but only because of a small spear I picked up in Portugal that destroyed the rim tape (and the tube), then made a noticeable gash in the rim!

The front is original - never changed it.

It's there to protect the tube from the spoke nipples.. so I guess, unless it perishes then it's only going to need replacing if you have a problem with your nipples.

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Never underestimate the power of stupid people in large groups.