Stiff bike, stiffer than the S2, WAY stiffer than the Six13. My low back hurt a bit after 25 miles of hammering, but then my back hurts much of the time when I first ride a new bike. Then it seems to adapt and it's fine. That's odd, because it seems to be set up just like my other bike.

Rear triangle isn't nearly as vertically compliant as the Six13, but this bike is lighter and it does climb better. The Six13 was starting to feel a bit mushy to me at times. This bike feels too stiff. I'll get used to it. It really takes me a month to figure out if I like a bike.