What's the bmw g20 wheel size?

The BMW G20 comes witH18 to 20 inch diameter rims depending on the trim level. Usually the higher trim options with the larger engines come with the larger wheels as well. If You are in the market for new wheels then most 18 inch to 20 inch wheels should fit on Your G20 3 series with no problems. In general You do not want to go more than 2 inches larger than stock though because that is where You get rubbing when You turn or go over bumps. That can cause Your tires to rub against the wheel wells and wear them down faster so You will need to replace them more often.