b) Stick with your 1/2 IM plan for now, and really training for IM is mostly like 1/2 IM training (at least my model) up until about 12 weeks from the IM, and that's when you start to pile on the bike miles--your run, swim and bike "bases" will be there.

Think of it this way: a solid 1/2 IM'er has about the same swim and run fitness as an IM'er--both should be swimming lots of intervals, running tempo and bricks, and riding HARD most of the time.

To extend that fitness to prepare for IM, you are adding a bit more swim volume (depending on how good a swimmer you are), a bit more run volume, but your bike volume will go up by 2-3 hours per week.

Most solid 1/2 IM'ers can whip out a century ride just as easily as someone who's training for IM, PROVIDED that they are riding HARD when they ride. If not, well then, not so much.

A lot of these statements depend, of course, on which 1/2 IM training plan you are using. What I am accustomed to makes it pretty easy for me to "flip the switch" that says NOW I AM TRAINING FOR THE IRONMAN RACE.

Example: up until about 2 weeks ago, I was holding steady around 12-13 hours per week of training, which is solid 1/2 IM training (you can substract about 1.5 hours from that which is my strength training, so maybe 10.5-11.5 SBR). Now that I am officially "in training" for Desoto Triple T, which effectively is like spreading an IM over 2 days, I've moved up to 15-20 hours per week, and most of that is coming from bike volume. After that I have IMLP, and all I will need to do is throw in a few 5-hour rides.

The other reason for holding volume to 10-12 hours per week as long as possible is for those of us who live in cold climates. As long as you are working appropriately HARD (which is fine to do on the bike all year long, contrary to some opinions--riding slow just teaches you to RIDE SLOW) and working to keep up your Functional Threshold power, extended those rides during actual race prep phase is really no big deal. REALLY! I've spent the last few winters not riding longer than 2 hours on the trainer (as my "long" ride), and I can bust out the door in spring and bang out a pretty solid 3-4 hour ride, no problems.

By the way, I'm not scheduled to ride longer than 4 hours in preparation for TTT. I may anyway, just because I can, but there is no need for me to ride longer until those last 8 weeks or so before IMLP, because I have the goods to back it up.

Who's training plan are you using?

Ironman training will beat you up--it's supposed to do that--so why would you do more than you need to until you NEED TO?

Train for your 1/2, develop some speed. It's EASY to add volume/endurance for 8-12 weeks. And that's the difference between 1/2 and full IM training.

Good luck!