I dunno
I can can do 40-50 miles before breakfast without any problem (and do this a few times a week), but I still find 100 miles to be difficult. I dont know if its my age (40), bike fit or saddle, but my lower back and butt start to ache enough at 80 miles to want to call it quits.
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2005 Lemond Sarthe
2000 Trek 2300
Old Nishiki built up with Sora Brifters & Campy Wheels
1999 Giant ATX 880 MTB