A powermeter may be on the expensive side, but with all the other stuff we justify spending $1500 on (i.e. a set of carbon wheels), you cannot find a better training tool.  If you use it to even half it’s potential, it’ll completely change your outlook on training and racing.  You’ll gain so much more in the long run by using a power meter than throwing some money at some Zipps for that immediate gratification.  Here’s a few reasons why I can’t live without my PowerTap (in no particular order):

1. You learn exactly how long you can push a certain wattage.  This is great for pacing yourself through your intervals or time trials.

2. When you lift weights you don’t put an arbitrary amount of weight on the bar and lift until you hit a certain heart rate.  Why would you do the same with a bike?  Power lets you know exactly how much "weight" you’re pushing. When you want 400watts for example (this may be your LT), then you pedal until you hit 400 watts.  No guessing, no variables to factor in (like an HR monitor)

3. You learn that you never surprise yourself.  You never all of a sudden pull out a 20minute 600watt effort (even though you  felt like you did).  Just like you never go to the gym and find that you’re all of a sudden doing bench press reps of 25% more weight.  A power meter helps you realize your limits so you can use your energy more wisely.

4. It helps you learn about your body.  You can link all sorts of external variables going on in your life to how you’re riding (late nights, what you ate, stress at work, too much boozing, medical conditions, etc).

5. You can track your progress.  Test yourself every 6-8 weeks to track your improvement to see how your body is adapting to your training.

6. You know your exact training zones. Unlike training with HR, it doesn’t matter if you’re tired, you had too much coffee, getting sick, etc.  There are no variables in the output that your powermeter is giving you.

7. You can optimize your pwr/weight ratio

8. It allows you to gauge your strengths and weaknesses better.  You can download your data onto your PC and look at the graphs after your workout or race.  You can see where you faltered and why.

9. It tells you if you’re "actually" riding good or bad on a given day, not just "feeling " good or bad.  I can easily tell if I’m getting sick or tired by how my power output by the baseline data that I’ve collected through previous rides.

10. It takes the variables like wind, hills, etc out of the equation.  A watt is a watts – well, almost.  I’ll get more into that later.  See this post

11. You can accurately track Kilojoules burned so you know how much you need to replace for optimal recovery.

12. You realize how little work you do in a bunch ride.  This can be either a good thing or a bad thing – depending on the purpose.  Sometimes I challenge myself to see how low my average power can be in a race.  The lower it is, the more gas I have for the finish.  See Train Aggressively, Race Conservatively

13. The feedback is immediate.  This is great for the short high intensity intervals.  A HR monitor lags by 15-30 seconds because your heart will slowly increase its response to the effort you’re putting out.

14. Using a HR monitor, I can push myself to 180bpm (for example) for a certain amount of time.  What it doesn’t tell me is that my power is decreasing throughout that time (because I’m over my lactic threshold ).  Even though it feels like I’m pushing just as hard, the powermeter is telling me that my power may be decreasing even though my HR is steady.  No wonder I always get caught on that flyer I take in the last 2km of a race.  I’m only pushing 200 watts by the end of it!

I could go on and on…gotta love the powermeter