There are a couple of differences between the Sun and the Surly that may be worth noting. The Sun has QR binders built into the frame sockets that hold the rear racks. This eliminates the need for Xtracycle's Whatchamacollars (a detail, but a nice one). The front end geometry of the Sun is also less agressive. This means that it will not feel like a fast mountain bike when unloaded or lightly loaded, but that it will handle well at low speeds with heavy loads.