They weern't unused we're they? didn't they start when you used the oldstyle outrun bike arcade machine gear? or something? (Cant remember correct name)
Yeah, it was this. Whenever you used the Hang-On and Super Hang-On Extreme Gear, these tracks would play instead of the standard track themes. Or, at least it was like this in the first Riders. I'm not sure if the same happened in ZG.