We do close to 100 van suspensions a month and I have to say the least popular wheel size is 18. Inch , logic for that I can’t be sure. 20 inch generally cheaper per inch to buy, tyres also cheaper . The standard offset on 16 And 17 inch wheels are between 50 and 60 mm but after market generally 35 to 45. . A lot of our customers put 20 to 25 mm spacers to fill the arch gap with standard wheels.