It sounds to me like some passive-aggressive behavior on your wife's part - some control issues, perhaps?

Bringing up riding, saying that she wants to go on a ride, waiting until it is too late for you to go on a ride by yourself, and then saying that she doesn't want to ride effectively is a way to control your riding.

Is there some resentment about the amount of time you ride, or that you have a GREAT TIME (as reported herein) without her? Or are there basic issues of which the riding issue is simply a symptom?

Is she seeking more attention?

Perhaps this is a bit far out, but that is certainly one possible interpretation of her actions.