Do you care what your max heart rate is?

What is your maximum heart rate? Are you using the "220- your age" formula, or the Karvonen formula to estimate? Do you really care what it is? After all, what does max heart rate have to do with your training zones? Very little, actually.

 The first thing to bear in mind is that estimating your max heart rate using one of the two conventional methods mentioned above can be off by 15-20%. That's a lot! And once you get that number, what do you do with it? Many coaches estimate that your Lactate Threshold (if you're a trained athlete) will be around 85% of your maximum heart rate. That's another "estimate" that can be way off, so now how far off the mark can you be?

If you really want to dial in to your training zones, find a local college that has an exercise physiology program and see if they'll use you as a guinea pig and do a blood borne ramp test. They'll get you on a treadmill and increase the incline every couple of minutes and take a blood sample from a prick in your finger. That test will be pretty spot on. If you don't have access to such testing, you can do a ramp test at home that will get you pretty close.

For a good estimate of your Lactate Threshold on the bike, warm up well on your indoor trainer. Then start a 30 minute time trial at the maximum effort you can sustain for the 30 minutes. When you get 10 minutes into the test, hit the lap button on your heart rate monitor and continue on. At the end of the test, find the average heart rate for that last 20 minutes (the final lap). That will be the estimate of your lactate threshold. From there you can calculate your training zones:

Zone 1 Less than 81% of LTHR
Zone 2 81% to 89% of LTHR
Zone 3 90% to 93% of LTHR
Zone 4 94% to 99% of LTHR
Zone 5a 100% to 102% of LTHR
Zone 5b 103% to 106% of LTHR
Zone 5c More than 106% of LTHR

For running, you can add 7 to the Lactate Threshold HR that you got from this test or do the same ramp test above, but running and calculate your zones as follows:

Zone 1 Less than 85% of LTHR
Zone 2 85% to 89% of LTHR
Zone 3 90% to 94% of LTHR
Zone 4 95% to 99% of LTHR
Zone 5a 100% to 102% of LTHR
Zone 5b 103% to 106% of LTHR
Zone 5c More than 106% of LTHR

Either way, it seems to me that maximum heart rate has little to do with effective training. Your Lactate Threshold (or the point at which your ability to continue on in your race is impacted) is more of an important metric to measure and train by.