There's the Rally America Sno*Drift, I think it's in Houghton, MI, but you aren't going to be able to just ride unless you are licensed. Usually if an event is sanctioned at all that is what you are going to find. Besides, if you want to go along for a ride that's one thing but if you want to co-drive you have to know what you doing. Anything less and a driver who lets you co-drive really deserves what will likely happen to his/her car. A co-driver is meant to be much more than a ballast to preload the suspension.
