Wow, that is a very good price for the 38x15.50 and pretty dang good on the 38x13.50 as well. I'm guessing they have some inventory they are trying to move? I checked all around where I live and couldn't get those prices. I even checked some internet sites as well and by the time I paid shipping they weren't any cheaper.
I am running them on a 10" wheel and don't have any issues. I believe some other on here are as well. I know it's not ideal but there aren't many 12" wheels out there.