Originally Posted by Barrettscv

I find that my ability to maintain sharp mental focus is my biggest issue.
But my ability to hold a reasonable conversation really declines as the miles add up. I also am less focused on directions and my surroundings.
My ability to keep a target cadence and speed also starts to decline as I ride. Often I'm losing focus at 90 miles. Sometimes I'm losing focus beyond 50 miles if heat, hills and wind are a factor.