Hi. I took delivery of my EV6 GTL2 in June and immediately purchased a set of winter wheels so I had them ready to put on this winter.
I went for Fast Wheels EV01+ 19x8.5 +48 offset rims with Michelin X-Ice Snow tires in 235/55R19. They fit well, but the +48 offset on the rims I bought is the most I would go. The wheels sit noticeably further towards the outside of the car than the stock GT2 20" wheels (15mm further out if my math is correct). A +45 offset would look too far out in my opinion (for a normal wheelset), and a +40 offset would be well outside the wheel arches. Also, based on the specifications on the inside of the OEM GT2 wheel, I can confirm they are 20x8 +57 offset.
None of the global models of EV6 come with an 18" rim from the factory, but I've seen a few people put 18" rims on their EV6 without issue. I went for 19" rims because I didn't want the look of a ridiculously huge sidewall on the wheels. I was going to wait for the Nokian Hakkapeliitta R5 EV winter tires, but Kal Tire told me the ETA is end-of-October for those tires, and that's just too tight a margin going into the winter season. I ended up ordering a set of Michelin X-Ice Snow winter tires in 235/55R19 from blackcircles.ca for the equivalent of $247 per tire before tax - they were on a good sale a few months ago. I had these tires on my Stinger for the past two winter seasons and they were very good. For rims I went for the Fast Wheels EV01(+) satin black, 19x8.5, +48 offset, 5x114.3mm lug nut pattern, 67.1mm center bore. These are available from wheelwiz.ca for $351.99/rim, but my local Kia dealer price matched the rims, so they brought them in for me, along with the tire pressure monitoring sensors. These wheels have the correct lug nut pattern, and the exact hub centric center bore for the EV6, so I don't have to keep track of hub rings when mounting the wheels. All in, it's a relatively expensive wheelset (~$2,652 CAD before tax), but it should suit the car well.
Dropping down 1" in wheel diameter increases EV efficiency by ~5%, and aero wheel designs (like the EV01) increases efficiency by another ~5%, so I should see a ~10% range increase with the winter wheel setup. This is of course ignoring the slightly higher rolling resistance of the winter tire tread pattern, the lower temperatures in winter causing less range overall, and the extra drag of the roof box I use during the winter. The range does not seem to be negatively effected from just the wheel swap though, as I recently did an ~830km road trip along a hilly route, averaging between 100-120kph, and the car did 5.30 km/kWh - which is very good for highway driving.
