id think it would have to be really small for it to be legal. kids ride around on their 50s where i live all the time, even their 250s and 450 bikes, where i live the desert is a big thing and its common. i guess it depends on the area u live, im not sure about sacramento, but here i was seen riding a 250 quad around my block by a police car and he didnt seem to mind, then again im in a small town and sacramento isnt so small so id say as small as u can get, maybe even no dirt bikes period. you could try asking around like at ur local bike shop, chances are they have the official statements.