A 50 series tire is shorter than a 60.
The first # 245 is the width.

See 245 or the 1st # is the width of the tire in M.M. I think ?
But the 2nd # is the height to width ratio meaning that the tire is 50% as tall and the tire is wide or 60% or whatever the 2nd # may be.
And of course the last # 15 is the rim size.