I currently ride 100+ miles a week. Usually 3 25 milers, a 40 miler, and maybe a 10 if I have time or get bored. I average 15.5 to 16.5 depending on the day.
I'd like to ride in the Tour De Fresno in September...I'm sure the 100 mile ride is too much mostly because of the climbing but was considering the 75 mile with less climbing. I could also opt for a 50 mile that's flat.
How do you know you're ready? Apart from actually doing a test run of the course?