Difficult to estimate. Bought a large stock 2017 Suburban tire. I've tried several times to follow the "formula" for the calculation, but I think it's incomplete. Please provide a conversion table. Our tires turned out to be about 0.5 to 1 inch larger than the plus size and I missed the return window by just a few days. One of the photos in the description says the size is suitable for SUVs but clearly not for a full size conventional car. That would probably be great, but there's no way to know.