My tire is 26.5". I ordered size 30-32 and it seems to fit perfectly. The material on the back is a soft fabric that hugs the hoop and is long enough to cover the bottom of the hoop. I don't know how a smaller casing would possibly fit my tire. I didn't give it 5 stars because there is no strap on the back to secure the bottom of the tire from gusts of wind.
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