I didn´t check the instructions for Yamaha road bikes with bigger tires but I noticed it too...then looked at the tire. It´s a pretty big tire on the back...not far from the aspect ratio of big bike tires and mine is pretty sturdy (happens to be an IRC made one instead of Dunlops) The front tire is smaller and I can see why it might be diff. and higher for more weight The rear one holds much of the weight all the time I would guess with or without a rider on the back. My more experienced brother in law says to check the tire pressure weekly as tires are tres importante´ to safe riding and I do. I keep both the front and rear at 29 pounds though had to add air when the temps here dropped from the 90´s to the 70´s finally this fall. Lance