I completed my first ironman last year in 13h13 with an 7:30 bike and a 4:15 run using the trifuel super coach training schedule. I'm planning on another one in maybe a year or so when my schedule frees up and I would really like to do the bike in less than 7 hours this time. I've been looking around and it seems the best way of speeding up the bike is with interval sessions. Do you guys recommend doing a weekly mix of interval sessions combined with longer slower rides (in the 75% region)? Or would it be best for me to spend say 3 months working on base fitness and then focus entirely on interval training?