There are many ways to test and capture this data. the key is to know your training volume and history. For the sake of this conversation, here is one that you can apply this weekend:
Weigh yourself prior to the test session.
Ride at an even tempo (you should be completely aerobic - you should be able to sing to yourself or talk to your training buddy) for 40-50 minutes
Complete 10 x 30 second acceleration (not a sprint) with 30 second recovery
Complete a ten (10) mile time trial (ideally 5 miles out and back); there are four data points you will want to capture:
1. Maximum heart rate achieved
2. Average heart rate of the entire 10 miles
3. Elapsed time
4. Total amount of fluids consumed
5. Post weight
Cool down 15-20 minute even tempo; easy spin.
The reason for the body weight evaluation is to make sure that dehydration or over hydration didn't negatively influence your testing numbers. If you would like a copy of our Sweat Rate Calculator, please email me directly at firstname.lastname@example.org
If you have any questions or need anything clarified, please post me back here on this forum.