Hi I have a 13 fz6r which came factory with the bt021 on it. I have over 6k on these tires and I'll be looking to replace them. I am having a great deal of difficulty finding these tires. I have found the front but I can not find the rear in the 21s. I have heard that the 23s are the replacement. I have also been recommended the q3s because of the dual compound. I really want a good tire that will get the mileage my 21s did. Over all they were a great tire in all conditions. I'm not an overly aggressive rider because I mostly ride 2 up. So all suggestions are welcome. Motorcycle superstore definitely has the best prices but I don't know which will be best.