I'll note some design factors you should take into consideration.
Notice the size and shape of the feet. They have very little surface contact and are able to spread any force so far. A wider round or square foot would be able to resist applied forces better than this rectangular foot.
I assume the round or square foot you would use has 3 and 4 bolts respectively, which is better than 2.
Typical bike racks in Chicago have 7 inch radius or 6 inches squared feet.