Hateful thing! Beyond 20 miles it was uncomfortable, beyond 40 miles it was unbearable. I did once do a 50 miler on it which involved a lot of standing on the pedals towards the end. Despite trying all sorts of different setups I eventually had to give it up as a bad job. The B17 it was replaced with isn't perfect by any means (I've finally come to the conclusion it's too wide for me) but has been good enough to do a few century rides on, including my personal best of 131 miles. Currently giving a Brooks Team Pro a try. It feels better for me shape-wise but will need some breaking in.