ridinbikes, going back to your initial post I can completely empathize of your concern of getting dropped. Though I do not race I was invited to ride with a group several years back that is much more veteran than myself. For several years I was getting dropped within the first few miles and even on days they went a little easier I just did not have the endurance to hang at their speed on routes greater than 60 miles.
But just as bgoetz pointed out there are many that follow this similar type of plan using longer interval times. Just as he pointed out I found that training indoors provided the best place for me to achieve this goal, but that is mainly because there are few places in my area outside that one can travel at the required training intensity without disruptions.
I just posted on my blog the other day what I try to follow as a routine. I started much like bgoetz pointed out with a couple of days of the standard 2 x 20's combined with longer weekend rides at a lower intensity. Over a period of a year my body has adapted enough to extend the intervals in several ways.
http://thecyclingaddiction.blogspot.com/2011/09/fall-into-place.html
Maybe there is something within that post that can be helpful as well in addition to what bgoetz and others have pointed out. I can say that by following these principles that my 2011 season has become one of my best for endurance events. I have not quite reached my goal of doing a sub 5 hour century, but when I am fresh I can easily hang with my group without the fear of being dropped.
Not to boast, but a few weeks ago I was on a group ride and came fresh, which is rare, because I missed some of the weekday training and those veterans were really having trouble holding my wheel. So this really does work as long as there is consistency and honest applied effort at the sustained intensity levels during those training sessions. I still have a long way to go myself so you can bet I will be in the
house of pain training each week all year round.
So keep in mind about doing this type of training you will still get dropped for a while even as you improve because you will take with you some fatigue to those rides. If you are fatigued and then try to hang with them you may take yourself into a training hole that requires greater recovery and thus interfere with those crucial training days. I learned this the hard way and finally got used to being dropped and riding at my own pace the remaining miles. I use my power meter to govern my intensity on the group rides so I do not overreach.
By the way the outline of my schedule on the blog is a goal and I do not always hit that goal because of work and life stresses or because of fatigue. Don't let those things disturb you. We all have less than perfect training days now and then, but it is the continual persistence that will eventually help you reach your goal.
For instance yesterday my goal was to do 3 x 20's at 90 to 91% FT.
What actually happened was 20 min. @ .95IF, 20 min. @ .91IF and 10 min. @ .8IF
Since my time is limited I use no more than 5 minutes between intervals.
I did not hit the goal on the mark because it was my turn to cook dinner last night and because of fatigue from previous training sessions. But this does not concern me because it was still a pretty decent training session for a recreational guy.
disclaimer: I am not a training guru. I am just a recreational cyclist trying to improve. /img/vbsmilies/smilies/smile.gif