Which is the wider tire? 4.50x18 or 110/100x 18 ? How are tires meaured? I know the last # is the rim size but what of the other two? Height and width? In what units? And if 110 is metric, why on earth are they mixing units because the rim is still 18 inches? I'm looking at a Pirelli MT16 for a rear tire for rocky mountain riding. What's the widest I put on a cfr450r? (I have a 18 wheel) Any other tire suggestions?