Check the backspacing.
A real front GNX wheel will have something like +15mm offset bossed on the backside of the center section.
A real rear GNX wheel will have something like +23mm offset bossed on the backside of the center sectiion.
A GTA front wheel will have something like 0 offset bossed on the backside of the center section.
A GTA rear wheel will have something like -19mm offset bossed on the backside of the center section.
(Don't quote me on the offset dimensions.)
Real GNX wheels have the center section welded to the rim barrel like the early year GTAs (87 and prior I believe). Look for the weld bead on the backside of the wheel. These are the wheels without the "dimple" in the periphery of the cross-lace. If the wheels have the "dimples", it's certainly not a GNX wheel.
If you're looking for authenticity, be careful. The early year GTA wheels can be modified to move the center section to GNX backspacing specs and rewelded. That's what I sorta did. However, I would never advertise mine as real GNX wheels. Also be careful of others selling these type of wheels. Not saying they're shady sellers, but I assume some just don't know any better and think the GNX wheels and GTA wheels are exactly the same. As described above, they're not.
Hope this helps.
Mike
