Follow-Up:
I think you've been mislead -- Continental specifically recommends that the Rialta only have 195's on the front due to clearance issues. The 215's on the back are to better handle the weight. I believe even the new 2002 Rialtas that have bigger wheels (16" instead of 15") still have 195's up front and 215's in the back. They account for the increase in wheels size by using a lower profile tire so it will still fit in the front wheelwell. If all of your tires are the Contrans model and they are exhibiting premature wear, bubbling, or cracking of the sidewall near the treadline, Continental will replace them with the newer and better Vanco models for a prorated cost. I was able to replace all four of mine for less than $170, most of which was the cost of mounting and balancing. Mine had cracking on the sidewall at the treadline and one of the tires bubbled. Call Continental at 1-800-TIRE-FIX and they will even call your local Continental dealership and make an appointment for you if you press them. It might be good to do that, because most local dealers don't know about the specific tire requirements of a Rialta, but Continental does and that way the dealer can hear it from the horse's mouth.
Here is a link that might be useful: MotorHomepage Rialta Resource