215s will be way to narrow for an 8" rim, as well as being even shorter than a 235/255 tire with the same aspect ratio. A 255/70/15 comes out to a 10.5" section width and is right at about 28" tall, give or take a 1/4" either way depending on brand. A 235/75/15 would also be an exellent choice, but I wouldn't go any narrower than that with an 8" wheel. Another option would be a 30x9.50x15 C floation size, which will give a good ride and still keep load capacity. That's what I'm running, on a set of 15x8 Blazer Ralleys.
