I've got a BT-20 on the front with about 7000 on it. I just took the wheel off the bike this morning & I'm going to get a new tire today. I've been running the BT-21 on the back for the last few tires. I'm happy with the way the Brdgestones feel but, I'm not getting anywhere near 10000 miles of wear out of the back tire. Around 4000 miles. Was going to get a BT-21 to replace the front BT-20 with, not sure now. I like the tread pattern of the 21 better than the 20 but if the 21s don't get good mileage maybe I'll put a BT-20 back on. I know you aren't supposed to run two different grades of tire on the front & back but, I have done this before on my Bandit 1200. I'm wondering about running a BT-14 or 16 on the front with a BT-21 on the back. What do you think?