Joined: Apr 2005
Posts: 971
Likes: 401
From: Northern CA
Bikes: Cannondale tandems: '92 Road, '97 Mtn. Mongoose 10.9 Ti, Kelly Deluxe, Tommaso Chorus, Cdale MT2000, Schwinn Deluxe Cruiser, Torker Unicycle, among others.
Saddle height is high on the culprit list. Too high causes the rider to rock side-to-side on the saddle. Not good for your butt, or much else for that matter.
If you have different leg lengths, did your fit get adjusted up for the longer leg?
No change in pedals or shoes, right?
Age and change in diet may be other contributing factors as well.