I have not found the answer to this question as yet. When I did my longest double, 19 miles one day and 33 the next, my tail bone was aching for the next two days. Even though it didn't hurt that much when I was taking the rides.
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"Too often I would hear men boast of the miles covered that day, rarely of what they had seen." Louis L'Amour
There are two types of road bikers: bikers who are faster than me, and me. Bruce Cameron - Denver Post