Well, I took the advice of other reviewers and ordered one size up. Sometimes that works out and sometimes it doesn't. When the box arrived it had a list of tire sizes on the side for each of the various covers, and sure enough my tire size was listed on the next size down. Did I make a mistake? No! These fit great IMO. They are SLIGHTLY roomy, but reach right to the ground and I did not have to fight to get them on. The elastic holds them snug around the tire. The smaller size may have "fit", but my guess is they would been tight and may not have reached the ground completely. Anyway, I am happy. They seem well made, but of course I cannot report on wear until they have a chance to do so. There is an elastic cord that connects across the bottom at the back to secure them, and that is the only thing I don't like. Very difficult to get to with the cover in place. You kind of have to "hug" the tire and secure it without looking, or climb under and get all dirty/muddy. Don't know how else you would do it however. Maybe practice will make perfect! My tires measure exactly 30 inches across and I bought the size for 33 to 35 inches.