All good things to know and think about, thanks LW! I didn't know about the pedaling thing...I'll definitely want to keep that in mind in the future. I've thought about the benefits of flat pedals off-road. I need to learn to keep my feet from flying off the pedals when I hit bumps, though.

I'm thinking it's probably the bike size, though. Last week when we went out and I was on my larger Cdale I didn't have any unreasonable pains (rode 65 miles on my road bike the following day), aside from my bruises.

Sat. was a MUCH easier ride (mostly on the rail trail, just a little bit of easy and really slow singletrack), but my back was angry for 3 days after that. That's the longest time I've been on that bike, so I suspect that that's the issue. The pain was concentrated in the middle of my back, not my lower back or arms (though it started to sort of radiate outwards after a day or so). Until Sat. I never did more than 4-5 miles on the weds. night rides, so I was never on that teeny bike long enough to really stress those mid-back/shoulderblade muscles.

I think we are going to try DS on the tiny Salsa. It will probably be a really perfect fit for him, since I think he's right around 5'.