size 160/60R15M/C
speed rated 130 mph Load rating 677 lbs
http://www.bridgestone.com/products/motorcycle_tires/products/battlax/th01.html
But for a much-larger rim width than our stock wheels at the rear especially, the tread profile will not be what you need to enjoy the stability and benefits of radials. It wouldn't be safe on our width rims. Think of a three-sizes too-small suitcoat-you may be able to button it, barely, but it won't look good or be comfortable. So, if you have to widen the rim, go to a larger-rim, 17" or 18" too.