Have you been cycling regularly over the past couple of years, or are you picking it back up after a long hiatus?

Might simply be that your muscles and hindquarters simply aren't strong and/or toughened up sufficiently for anything more than brief stints on the bike. It's not as though 20mins should itself be causing any thing, but 40mins could.

If the mild aches are beginning to fade in a few weeks (as you strengthen the muscles involved), it's a good bet that the fit isn't the problem but rather usage is.


Myself, several years ago I picked up a "beater" bike for occasional around-town jaunts, mostly in the sub-20mins range. It was a very low-end bike that's typically sold for ~$125 in the big box stores, with a relatively upright position, swept riser bars, fat saddle, etc. Very comfortable for 20-30mins. But for anything longer, it got tiring and a little achy. That is, for the first couple of months I began riding it. (But I'd been off a bike for a few years, at that point, nursing some injuries.) After a couple months went by, those minor, short-lived aches all but disappeared as I got stronger and more used to time in the saddle. Fit was perfect, basically, and the issue (in my case) was muscle fitness.