GM and **** used 17.5 inch rims. Those I've seen are strictly one-piece, no split rings. The GM rim came in at least two offsets, one of which may not work on the front end. Match your current rim's offset for best performance. A number of manufacturers produce an 8 x 17.5 inch radial. Yokohama has them in highway and knobby ribs. TireRack advertises them in mags like Road & Track. M.E. Miller Tire in Ohio (a This Old Truck advertiser) has an 8 x 17.5 in a bias ply.
THE HUBCAP STORE in Easton, Pa. has a decent selection of the 17.5 inch one-piece wheels -- as well as thouands of others -- all USED but in good shape.
These rims generally measure 5.25 x 17.5.
