[Willowbeast]

I know we are talking about RDX, but my MDX has 20" with that said, I have 18" dedicated winters. This helps explain, snowshoes are wide, keeps you "floating" above the snow, not good for vehicles, a small road bike tire would pierce through the snow down deep (mind you slicks don't give traction, I know). So you are better off and will always be better off with narrower tires if you are in a snowbelt location using dedicated winter tires.

 

[Willowbeast]

FWIW, we also have a 2018 RDX but its stock tires are 18". When we bought it CPO we got them to throw in a set of winters. I would have preferred smaller ones but they gave us 18s (16 or 17 would have been better) but I won't complain when it's free. Best of luck