bike pacing for energy conservation?

I really like this article on IM race day execution by coach Rich Strauss, which includes a section on bike pacing, among lots of other good stuff...

http://www.cruciblefitness.com/etips/IMHowTo.htm

Talking speeds is all relative.  Sounds like maybe your haven't done HR threshold testing to determine your HR zones?  I recommend doing that in order to make sense of HR-based pacing guidance.

Personally, I'd rather "work" the downhills and "conserve" on the uphills.  Of course, this all depends on the specific hill, terrain, and course, but I find that putting some effort into the downhill can very much help you carry momentum either up a following incline or across a following flat.  Think constant and consistent output of power, rather than turning the power on and off.

I almost always pedal at an even effort the whole time (some hills demand more obviously) but for IMLP last month I really didn't have the level of fitness I wanted so I made the ride into a total Sunday cruise.  Coasted down the hills, went moderate on the flats and sat up on the bars and pedaled easy up the hills.  It allowed me to have something when I came off the bike, even with limited fitness.

Would I recommend that approach to everyone?  No, of course not.  But for me with the concerns about pacing and fitness it was the best approach and I was very happy with the result.

This obviously depends on the couse, but for a course like IM MOO where the downhills are longish, I pedal for the first bit of it and then tuck in.  When you start to slow down to where you can get some pressure on the pedals, you start pedaling again. (This takes trial and error)  That way you don't lose any momentum for the next climb and have saved your legs.

In my own little experiment in shorter races, I have found myself gaining or not losing any ground on people that still pedal downhill when I am just coasting and staying really aero.