I recently changed tires on my R27. Some DPO had a 4.00-18 on the rear. It had rub marks from being too big, and both tires were weather checked. I fitted a modern 3.25-18 Continental on the front and a NOS 3.50-18 Continental on the rear. I realize that the rear is still over-sized compared to OEM specs, but the end result is that the transmission is less troublesome and the bike handles so much better. Why? Would a 3.25-18 on the rear make a marked improvement?