The 10.50 inches is the tire's advertised width, usually taken at the tread, not the sidewall bulge. And the 15 is the size of the wheel it's designed for.

GREENVILLE, S.C., Aug. 2, 2021 /PRNewswire/ -- The MICHELIN ® CrossClimate ® 2 tire is now available in sizes that cover most of North America's most popular cars and crossovers. The ...