Wheel — one damaged side's eaten by rust, say (7)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

One of these days I’ll remember that by is times is X, but until then I’ll puzzle my way through wordplay that doesn’t quite work. Wheel provides the shape of O, the one is I, and damaged side gives you the anagram DISE. Put them together, and insert that X.