If you go by the normal system of 220 - age, you will get a ball park figure to work from. Treating that for myself, I get an upper limit of 162, and If I ride at that for any length of time--- I can't. Energy, legs, breathing, body- in fact everything goes. However, I do like to ride constantly at 150, and can do, when necessary, for extended periods of time.

Your own limits of your own H.R. are for you to find. Every one is different, but Guage yourself up against your riding partners. If you can still beat them up the hills, Don't bother about the Heart Rate. If they are beating you, let them go- they are probably younger fitter or have a lot more to prove.

(on heart rate as a maximum %age- Don't worry too much as according to the formulas- I ride at 90% of my max all day, and that is supposed to be impossible for us oldun's)