the wheel is the same diameter (WM3 - 18) but the spokes are thicker on an N15CS. The nipple holes are larger for the larger nipples that go with the heavier (8 gauge?) spokes
in the parts manual - a complete Atlas wheel with brake parts is part number 25352
032322 - complete wheel for G15 Mark II
032323 - G15CS, N15CS
032324 - G15CSR (19")
Nipples for the spokes:
021693 - 650SS, Atlas, G15 Mark II, G15CSR (These are all road bikes and use the standard spokes)
021694 - G15CS, N15CS (These are scramblers and use heavy, off-road spokes)