I usually ride a road bike on major roads (majority with bike lanes), but recently I've been riding a 3 mile loop on my fitness bike (flat bars, upright geometry) through a residential area with squirrels darting to and fro across the roads. Today, I hit one with both wheels going 20mph+ - a solid hit, bump bump. Ahh, dang, shoot.... I look back expecting to see the damage, but I see the squirrel scamper across the road at full speed. I couldn't believe it. I'm 175lbs, my bike is probably 22lbs, he was hit twice, and he just trucked on like nothing happened. Wow. Cool. Dang.