If you want to really set your zones accurately, max HR is not the way to go. For one thing, even with the best intentions it's almost impossible to determine. Most cyclists set their zones off their lactate threshold, which still isn't easy to determine, but at least it's fairly accurate.

Here's a link for a good system for finding that and setting zones by HR as well as by power: http://trainright.com/cts-field-test...-calculations/