1) meaning to be driving in a Import (i.e. Honda civic) and to have 20 inchwheels on it
2) to be riding a bmx bike that has 20 in rims or a 20 inch top tube
1) "Man, we be rollin on 20'sup in this joint, ya hear?"
or
"Those 20's your rollin on are Bitchin!"
2) "man, i'm rollin on new 20's, check these bad boys out."