Quote Originally Posted by Juiceflight View Post
Top tube and head tube length could have something to do with it. However, the shape of the saddle can have a big effect on the angle of your pelvis. Think about how you sit with you lower back supported - the natural curve is preserved. If you sit slouched or allow your pelvis to tuck under (where the natural curve is rounded the in the opposite direction) it puts a lot of strain on your lower back. I rode on flat saddles for years and fought with lower back pain. Eventually I found a saddle that ramps up in the back that also has the right type of cutout. For me, the ramp allows my pelvis to sit at a more natural angle thereby eliminating strain on the muscles and vertebrae of my lower back. I can now ride comfortably in a lower, more stretched out position when need be because I have the right kind of saddle to keep my pelvis properly angled.
Just curious...but could you share what saddle it is that you're using?