Hey, I purchased a Felt Z100 for rec riding but recently started commuting with it. I am using a Topeak beam rack to hold my books and lunch for work. My issue is this: the beam rack keeps shifting and hitting my spokes. I have broken three spokes so far. I have the right rubber pads in the rack and have it as tight as I can get it. I would get another rack for the bike but it lacks the mounts for it so a beam rack is really my only choice. Any suggestions for how to stabilize the rack so it stops moving around?