As mentioned in the post above, my bike did not have mounts for a rack. I bought a seat-post rack, and immediately brought it back. Not only can it only hold half the weight, but you can't use any panniers with it, because there's nothing to keep the bag from rubbing against the wheel. Picked up a regular rack and told the LBS "You figure it out." They did and I've never been happier. The difference of weight on the bike has been negligable, but the difference in my own comfort is tremendous. No more aching back!