A wheel rim includes two annular sidewalls and a main connecting wall. The main connecting wall has two ends connected respectively and fixedly to radial inner ends of the sidewalls, and opposite radially inner and outer surfaces. The radially inner surface faces the hub, and has two axial surface portions and a middle surface portion that are preferably concaved toward the tire. The radially outer surface has two axial surface portions and a middle portion. The axial surface portions of the radially inner and outer surfaces define two force-bearing areas having a plurality of mounting holes. The middle surface portions of the radially inner and outer surfaces define a weight-reducing area having a thickness smaller than a thickness of the force-bearing areas. The force-bearing areas and the weight-reducing area are arched.