Heart rate confusion!!!

First you have to find out what your max heart rate and resting rate actually are (formulas of any sort are notoriously inaccurate). Check your resting rate when you first wake up in the morning for a few days and average the results. Resting heart rate is a good indicator to tell you if you ar overtraining.

Finding your max is harder and more painful. I reccommend using the ride- up- a- big -hill -as- fast- as -you -can- until- you- almost -puke method. Note: I found about six more beats per minute by using this method in a race with another racer hot on my heels. Max heartrate is a good figure to base pacing numbers upon. Although your lactate threshold heartrate is probably a better figure.

Leona,

You could also start paying attention to your perceived exertion. Try different efforts and after you've been working at that effort for say 5-10 minutes check your HR.  Do this at different times over the course of a week or so.  Then you should have a fairly good idea of what HR you should be working at.

Check out this website.
http://www.cdc.gov/nccdphp/dnpa/physical/measuring/perceived_exertion.htm

You should be doing most of your workouts in the 11-12 range of perceived exertion.

13 -14 - is hard, you could do it, but you couldn't hold a conversation, and you need to concentrate to keep up the pace.

15 -16 - This is where your breathing start to really change.  You start panting etc.  This effort level could only be kept up for 1/2 hour to one hour.

17 and up - these move up really quickly. Think sprints, all out effort, etc.

Hope this gives you an idea or two.

PS - Working out at a HR of 175 is very high, normally - I'd think you need to bring it down to around 150 for your normal workout zone.