Jeans and MX pants will last for only a fraction of a second sliding on asphalt. For abrasion resistance, you're stuffed either way.
Either get some kevlar jeans, or better still some leather pants/supermoto pants if you don't want to wear a 1 piece.
Either get some kevlar jeans, or better still some leather pants/supermoto pants if you don't want to wear a 1 piece.