[Jeff in Kentucky]

I used to ride with regular dirt bike tires in snow less than a foot deep- a foot or more messed with the steering and the back tire traction too much, and if you crashed the landing was somewhat softer.

When I was a kid, we would pour water on abandoned gas station pavement, and race around the pump island with regular bicycle tires on the ice. We could not afford to race motorcycles- too much money for all of us to have one and keep them repaired. Here are two guys that rode on lake ice, until one died while riding on the dirt:

http://www.snowmobiletrails.com/moto/index.html