Hi

Truth be told, IMO, one's max HRT is irrelevant and the many formulas that exist to determine it, speculative at best. Remember you are on a bike, which would make it very, very hard for you to actually reach your max HRT on as it is generally a non-weight bearing activity (as opposed to say running).

I've never really bothered to calculate or worry about max HRT. Whatever training I do, if I even wear a HRM, is based on something much more tangible and easier to calculate....Lactate threshold. It is much easier, and probably less dangerous/stressful to your system, to determine your LT instead of your max HR. For instance, one recommended method is to do a 30-minute time trial - when your heart rate stabilizes during that effort - that's your LT. Then building training zones around the LT number is very straight-forward - for example, you can train in a zone that's 80% of your LT, or 90% or whatever you choose for your goals. This is the method used by Joel Friel and others of ultrafit - a pretty respected coaching outfit in the US.

I think this is better than trying guess or punch up some number and saying, ok, that's my max HR.

Just my opinion, but of course, see what works best for you