I need to thank user TJS909 (again) for his post on the recent Central Valley Pratt Truss Bridge thread pointing out that Micro-Engineering's HO scale bridge shoes are actually the proper size for N scale. I dropped by a LHS today and found a package in the store's HO section, and compared it to a piece of HO track; the biggest shoe (they seem to come in two sizes) was smaller than the end of a railroad tie! Certainly in the prototype world a railroad bridge would smash or flatten a bridge shoe that small! I bought a pack of their N scale bridge shoes a while back and likewise they're too tiny for N scale; I'd either use them on a road bridge, or maybe convert them to mailboxes in my N scale houses.
Bridge bearing background information Bridge shoes are commonly called bearings in design and construction of bridges. Bearings come in all shapes and sizes. I've worked on several bridges in which the bearings ranged from a 1/8" sheet of lead to a multi-ton forged steel rocker assembly. These pictures of the Bellefontaine bridge in Ohio show some old style forged steel bearings. Picture 3 of this Flickr photo set shows modern elastomeric bearings on a highway bridge. Picture 6 of this Flickr photo set shows a steel roller bearing ready for replacement. This Chinese company shows a few of their bearings online. It also includes a brief explanation for the different types of bearings. Depending on the bridge you model, the bearings may be a visually important detail or they may be too small to notice. Certainly there is not a one size fits all bearing. It's entirely reasonable to use ME's HO bearing for a sufficiently large N scale structure. Conversely, the N scale bearing may still be too large for many N scale bridges. For more information and pictures, perform a Google search on 'bridge bearing'.
