Have fun on the new Tractor.
Whoops! I mean be hard working and productive on that new tool! IT IS NOT A TOY! I don't know what makes the better halves in our lives perceive these hard working tools that tire us out so much as toys!
But on to your question...The size of the tire might be due to the type of tire. My B2910 takes a wider turff than ag or R4.
My R4s are 12.4-16, but had I gotton turf tires they would have been 13.6-16.
If you are thinking turff, but actually have one of the others, this may be the reason. Check your owners' manual. Tire options are listed in the back of mine.
Happy tractoring!
Bill in Pgh, PA