This is another newbie Tri/Du question :)

I have an informal tri coming up in a week and a half (A "tri for fun" series) and have some questions about how to ride the cycling leg. The course is 11 miles and is mostly flat but with a few rollers. I've heard that a lot of people will ride road TT's in 3rds, ramping up the first 1/3, going hard but steady the 2nd third and then ramping it up on the last third.

Should the same general idea apply to the bike leg of a Tri as well? I know that my tendency is to start out too hard. However, the first part of the course has me wondering. It starts with a small climb out of the transition area up to a road that is mostly flat. The first 2.5-3 miles of the course almost always has a big tailwind. I live pretty close to the course so I've verified this. You can get up to insane speeds on it, sometimes as much as 5-6 mph above what one might do on flat ground. Early in the morning through the wind is usually good for 1-2 mph greater than the usual speed. Part of me wonders if I should go harder at the beginning to take advantage of this "free speed" I'd get from the tailwind while I have it. Or would I be better off saving my watts for the return leg that has a headwind (it's along a different road) ?

Not sure if I should always stick to the idea of riding the bike part in thirds or if the terrain would indicate a change of some sort.

You stand to gain MUCH more time by spending more energy while riding into the headwind than when you have a tailwind. It's similar to riding hilly road races - you'll gain much more time if you attack on the climbs, than if you attack while descending. I'm not saying that you should take it easy while you have a tailwind... go hard, but not so much that you can no longer maintain the same average speed once you hit the headwind.

From your course & wind description, it sounds like the wind will play well with the thirds rule. The way I would ride the course would be the same as any other TT I do:
1/3: hard, but at an effort you know you can hold for the whole course
2/3: assess if you can push harder and hold that same pace for the rest of the course
3/3: assess one more time, and again, go harder only if you feel like the new tempo can be held out until the end.

All said... I'm not sure if a TT-style energy dump via thirds rule is applicable to dong a Tri; shouldn't you be saving for energy the run leg? After all, I'm just a roadie that wandered into the tri forum for fun tonight =).