Heart rates are a good way to determine your training effort but only for someone who want to get a bit serious. If you ride for fun and pleasure dont bother.
I used to use a monitor to determine,
1. If i was trying hard enough during training (usually no)
2. To ensure i didnt over do the first bit of a race (usually yes, then blow up before the end, and crawl over the line with the strength of a 18 month old baby)
The actual number is not important - its very indevidual
- mine is low (both resting and max) and my mate was high in both cases - next to each other i would be 20 beat less than him, while trying harder.
To acurately determine your real max, you've got to work so hard you need to feel physically sick.
On the bike find a nice gentle hill, ideally about 4-5 mins long with a little kick at the top if possible
Warm up for 15 mins nice and gentle - but ramp up to at least 75% max at the end.
Without cooling down in between, ride at the hil, increasing the pace slightly with each meter - the idea being to hit your absolute max just before the top, then push over the top using every last bit of energy you have.
If you don't feel sick and fall off the bike in a gibbering heap - then you've not tried hard enough. Do it again. Really you should feel like your lungs are going to burst, your legs have been filled with acid and you heart is bursting out your chest.
Thats your real max, you shouldnt really be able to quite hit it during a race or training. I used to occasionally hit mine if i did very extreme intervals.
But not any more - it hurts. I just ride for fun - and slowly and gently, once i realised i had no natural talent or ability.
Its sport specific - so you might need slightly different figures for each activity (mine is also slight higher for running)
Also best done when you are fairly fit, and while it is not meant to change with training (instead your heart rate drops for a given activity level) its worth checking its the same as your fitness increases - or you learn to push your self harder.
Bet you can hit higher than 155