A lot of folks have been asking about pacing management around races -- hardly a surprise as we truly are in the thick of it now and across the coming months.  While I am unable to provide individual guidance in this forum, there are some important insights that I can help you with as you approach your events.  Here are a few principles to bear in mind:

• Experience helps.  I don’t view race pacing as an isolated event, and wisdom can be a great asset, as long as you learn from one race to another.  It doesn’t need to be race specific, as it is an art as much as a science, so ensure you practice pacing in training and apply lessons from your other race experiences.
• Most folks lack patience.  I seldom hear people tell me that they ‘wish they had gone out faster’ in races.  We used to have a saying in swim coaching that it is better to be the hunter than the hunted, and self-management and patience early in each discipline is almost always a smart approach.
• Your answer can never be found purely in metrics.  Let me make this really clear for you:

You cannot effectively pace in races by simply trying to hold a predetermined heart rate, power or pace.  This is not, and never will be, your most effective manner of pacing.

Ok, so how should you do it?  Here is my hit-list of pacing tips that you can keep in mind when approaching your various races:

1. Begin calm and settle.  Too many folks are too aggressive early.  Across disciplines, the first thing that you want to do is to ‘settle’.  Calm down and seek finding a sense of rhythm and serenity.  If you can do this, then your focus can be placed on form, terrain management and -- yes -- pacing.  Swim, bike, run - it applies to each discipline.
2. Building efforts.  In both standalone running races, as well as swim and bike disciplines of a triathlon, a building effort is nearly always superior.  Your mission should be to ‘deliver yourself’ halfway, or even two thirds of the way, and be in a place to hold great posture and form, and keep the pressure on.  Your perceived effort should build through the discipline or event..  The only outlier here is running off the bike in an IRONMAN, in which you begin with several hours of work always complete.  A marathon of the bike is more of a focused and consistent effort, with management in the back half.  I don’t advise trying to pace an IRONMAN marathon in the same way as you would a standalone marathon.  They are different events.
3. Use your metrics as a framework.  Your power and pace is an expression of your actual output.  Your heart rate is an expression of your internal cost.  Used in conjunction with each other, they become in-flight signals and cues of what is happening.  They shouldn’t be obsessed over, and they shouldn’t shackle you.  They should be met without emotion, and be simple data points to help in your overall management of the race.  You can only truly utilize these metrics if well rehearsed in training sessions, but they can be useful to know as you navigate the day.  An example would be looking down at both metrics 25 miles into an IRONMAN.  If you see a heart rate of 155 bpm, when you know that your typical endurance effort is 120, then it is a signal to consider.  You need to settle down a little, and also potentially back off.  Equally, if you see 250 watts on your power meter, and your assessed maximal steady state (FTP) is about 265 watts, then you will likely need to back off a little.  You can ask yourself the question; ‘what are the chances I can hold this output/heart rate for the next 5 hours?’.  
4. Self-Management.  The metrics and data points mentioned above are only useful when combined with ongoing self-monitoring and management.  This is something that can be trained, and is your number one pacing tool.  You need to be patient, honest and consistently checking in with yourself.  What did I say?  Wisdom is an asset.  
5. And finally -- let’s finish with a nice rule of thumb for you:

If you're unsure in the first half of a race/discipline, err on the side of caution and backing off.

If you are unsure in the second half, err on the side of pushing up and keeping the effort up.

That’s a nice rule of thumb.

Alright, I relent.  I can hear the noise from the peanut gallery already...  all of you power junkies asking for the percentage of FTP to hold in your racing.  I don’t believe this should be your driver, but I will give you a rough gauge.  It all goes completely out of the window as soon as you manage terrain, and are greeted with downhills, tailwinds, steep hills and more, but I will feed you what you want through the lens of customer service.  Here you go:

Olympic:  85 to 95% FTP
Half IRONMAN:  78 to 88% FTP
IRONMAN:  68 to 80% FTP
Ride strictly to numbers at your peril!

Cheers,
Matt