1995 VT1100C Honda rear tire replacement time...

I'm looking to replace the rear tire on my bike with a CT. Bike tire size is: 170/80-15 MT
I'd like to know what size CT I need to replace the MT with.

Your tire is the same size as the rear on my VTX 1800S. I went with a 205/65-15 Goodyear Triple Tred. Over 16000 miles on it and love it. Barely looks worn although it has rounded its edges off so it doesn't look quite as square as it did when I first put it on. Lots of twisties here in the Ozarks so rarely just riding straight.