Let me try this...
I'm still not sure exactly what the question is, but if I give a broad enough answer it might work. First things first. Always remember that the numbers on a tire are "advertised" size. What that means is if you take 10 different 31x10.50x15 tires from 10 different tire manufacturers, they would all be somewhere around 31" tall, and 10.50" wide. None of them would be exactly the "advertised" size. Some would be shorter, some taller, some narrower,some wider, etc. So everything you see may not be what you get.
If any of that works for you, and you still want to know about aspect ratio's and what they mean, let me know, and I'll try to make some sense of that too. In the meantime, lets have some fun. Here are some links to tire sizing charts. They can be real entertaining, especially if you want to know more than just tire sizes...
http://www.miata.net/garage/tirecalc.html
<A target="_blank" HREF=http://members.aol.com/agspeed/tiresize.htm>http://members.aol.com/agspeed/tiresize.htm</A>
<font color=purple>N2TRUX<font color=purple>
<A target="_blank" HREF=http://n2trux.coloradok5.com/>http://n2trux.coloradok5.com/</A>