Remember, Inflated dimension will measure differently than loaded dimensions. I would want to compare both tires on wheels, inflated, on a rim, OFF the car and see too...
The Yokohama site shows Overall width for the Avid S/T 245-60-15 as being 9.9 inches and the Tread width itself as 7.9 inches. Here is the link if you want to check it out.
Avid S/T:
http://www.yokohamatire.com/pdf/AvidSTBull.pdf