Here's some more specific data because I've just got back from a ride. I usually take flat land at about 2nd range, 7th gear. Once I approach a hill, I drop to 1st range. As I progress, I drop gears. But after a short time, my quads start to burn. When I tried to alternate like you guys said, I stood up and it felt worse. I'm not sure what I'm doing wrong, but my muscles seem to get sore pretty fast going up hills. Just a guesstimate, but the two hills that I'll usually encounter in my rides are about 1-2 miles long. They're pretty steep hills, but not very steep. And I currently have 26x1.75" hybrid type tires right now.