Try your 18" wheel on the GLC to see if it clears the caliper
Yep, that will certainly be part of it... I'll report back... just not sure if I even can because offsets may be entirely different. I haven't even purchased the GLC 43 yet, but 18's will be part of my plan. There is a decent amount of "smallest wheel possible" on the GLA forums. I suspect that someone here has looked into it on the GLC.Try your 18" wheel on the GLC to see if it clears the caliper