I have bought a couple of sets of inner tubes on ebay for cat trax. Mine are not the ribbed wheels but I don't see that would make a difference. One set of my cat trax tires are so dry rotted cracked they would go flat in a couple of days. Once I tubed them they work great. I only use that set on grass I do not think the tires would hold up to gravel or rocks. Sorry I don't have the size inner tubes I bought.
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Prindle 18 w/ wings, Prindle 16, Prindle 15, current
Hobie 16 in rebuild
2 Hobie 18 past
NACRA 5.2 past
Saint Cloud, Florida
member Lake Eustis Sail Club
http://www.lakeeustissailingclub.org--