getting low up front pretty much.. take out all your spacers, flip an upturned stem.. the importance is aerodynamic savings from having less frontal area exposed to the wind...

maybe its cause i'm young but i always hear about people having problems going from a road bike to a more aggressive position on their tri bikes, but i never experienced it.. i went from 13cm headtube with about 3 cm of spacers to 8.5cm ht and no spacers with little problem

A couple weeks ago I was lucky enough to have Dan Empfield (one of the guys who came up with tri bikes and their fits) take a look at my position on the bike. One of the things he said really made sense...

"You will be just as uncomfortable too low or too high on the bike"

It is not about where you should be, it is about where you are comfortable and so where you can stay and hold power. Yes, being lower is better for aerodynamics... but if you are so low you are uncomfortable then you won't be staying there, and you won't really get the aero benefits. Or you will stay and be stiff and that will hurt your run.

So how low should you be? Play with some settings and see where your body is happy, and that is how aggressive you should be.

A bunch of girls from over on Slowtwitch had a training weekend up at Dan and Monty's, and he just took a quick look. So it wasn't a full fitting, but I got some great feedback and knowledge!

I raised my seat a bit based on his advice, and the legs feel much better. And I just picked up a new stem yesterday to get more drop... I'll be putting it on the bike tonight!

The thing with aero position on a tri bike is that you have to USE IT. The most surefire way to figure out your best position is to do a wind tunnel test; however, if you have a power meter you can also try out multiple positions.

Aggressive positioning requires good core strength and low back flexibility. It's not always the most comfortable, but then again, it's not called riding a couch, is it?

Similar to what's already been said, my understanding of aggressive position has to do with body position. Not just being in the aerobar postition but also having the seat adjusted to the right height and horizontal position allowing the legs to be in a place where optimal power is achieved, you're semi comfortable, and the least amount of body surface area is exposed, ie good aero position. I'm guessing that's one of the major differences in TT bikes and road bikes since the geometry of the bike changes slightly making it easier to be in that "aggressive" position.