Maybe it's my meditation experience, maybe I've just been to too many concerts where there might have been something in the kool-aid, but:
It's those precious few opportunities to be on a stretch of open road after a good warm-up when everything syncs up and you're totally aware of the moment. What happened yesterday doesn't matter - yesterday doesn't exist right now. What may happen tomorrow doesn't matter - tomorrow doesn't exist right now. And you're aware of every blade of grass and dimple in the asphalt and cloud in the sky and the whole "scene" just syncs up. It is meditation and medication.
Of course, my luck being as it is, when I reach that zen-like state, a bee invariably flies into my helmet.