Would love your thoughts on my IM bike pace...

What ChrisM said x2.  Trying to hold a certain MPH on the bike can lead to a long 26 mile walk.  I use a HRM to set my bike effort.  In training I note my average HR on all long rides and how I felt after the ride.  I then use this information to determine my race day pace.  See my sig line for my thoughts of riding too easy.

I am from the "only done one" camp but echo what others have said. Pace by effort, not by speed. I knew going into my IM that if I stayed around 130 BPM I would be fine and if everything was right (weather, nutrition, etc.) I would be fine. Ended up at 16.4 MPH for a 6h 39m ride. Not fast, but within my goal range so a success.

I've always liked the IM race-day execution advice from Rich Strauss.  I copied his typical bike pacing advice below.  Here's a link to his coaching site to give him props.  http://www.endurancenation.us

To me, it boils down to this:  (Get a HRM) + (Learn how to use it) + (Follow the bike pacing advice below) = (Have a good day)

Simple.  :-)

Pacing

An effective pacing plan enables you to enter miles 16-18 of the run focused and prepared to not slow down.

Swim = Form
Your pace is defined by your ability to maintain good form.  Only swim as fast as you can maintain good form.

Bike = Patience and Discipline
Exercise patience and discipline to ride your race and ignore the athletes around you.  Your goal is to ride an 82 mile bike after a 30 mile warm-up.  You make or break your bike leg in the first 30 miles.  Be patient.

Miles 1-30

· Overall Goals: Settle into a comfortable cycling rhythm, establish food and drink strategy.
· Effort Guidelines: Pace should feel easy.
· Heart Rate Guidelines: Once the heart rate has settled from the swim, typically upper heart rate Zone 1.
· Notes: You should be holding back through this whole segment.

Miles 31-60

· Overall Goals: A continued emphasis on nutrition and hydration, as well as an overall assessment of how the day is progressing.
· Effort Guidelines: Pace should feel easy.
· Heart Rate Guidelines: Typically, Zone 2 effort.
· Notes: The goal of this stage is to maintain a steady effort at goal Ironman-distance bike pace.

Miles 61-90

· Overall Goals: This is the meat of the ride. Here is where early ride pacing pays off or takes its toll. Goal should be to work a little harder than goal effort. Athletes that have paced properly will begin to move up the field.
· Effort Guidelines: Pace should feel steady. Hills and rollers will see efforts up to moderately hard intensity. Avoid hard intensity.
· Heart Rate Guidelines: Typically, upper Zone 2 effort with short periods of Zone 3 effort when climbing.
· Notes: This is the key stage and where you will have to concentrate to maintain your focus. Early ride pacing starts to pay off and athletes receive a mental boost as they start to move through the field.

Miles 91-112

· Overall Goals: Athletes should maintain their cycling momentum and continue to eat. Almost all athletes will have lost their appetites and continued nutrition is essential for a strong run.
· Effort Guidelines: Pace should feel steady to moderately hard. There will be fatigue and stiffness associated with the ride. However, these should be manageable.
· Heart Rate Guidelines: Zone 2 effort with periods of Zone 3 effort when climbing.
· Notes: Athletes should maintain their focus on pacing, nutrition and aero position. Race fatigue can cause the mind to wander. Athletes should maintain a task orientation. If you have paced the bike correctly you should feel like you are "racing" the bike while those around you just want to get off. Take these good feeling with you off the bike and into the run course.

Ideally, you should get off the bike feeling as if you could have gone 5-10 minutes faster. Keep this fact in mind: it takes quite a bit of sustained effort to go 5-10 minutes faster on the bike.  But walk one mile of the run and you give this all back. It's OK to feel a little cheesy when you get off the bike.  A 42k run is a long time to make up for riding too slowly.