I didn't find time to call Hoosier, but I did find rim sizing elsewhere on their site for new Hoosier slicks, which is probably identical to this stuff (the Conti is just branding, I think Conti actually owns Hoosier and Hoosier makes all slicks with Conti written on the side?).
In any case, in "recommended rim width" for new Hoosier dry slicks, 265/645R18 is 9-10 and 285/645R18 is 10-12. So they probably work on 10's, maybe a little fat-looking
