I have my seat as far up as it will go without bobbing. I'll try a quarter of an inch or so.

I don't think I was riding any harder than usual, but it was on gravel so I may have been trying to keep my same pace and worked harder than I thought I was. . . if that makes sense. Still I've pushed all day long before on flat ground with a single speed, maybe I'm getting my gearing wrong. I'm trying to spin more, push less, but I have no reference on what my rpms are.