The LT315/70R16 MT/R with Kevlar measures 34.8" high by 12.3" wide. That is measured on an 8.5" rim, on a stock Moab it would be slightly narrower. See the info here and click the "Specs" column:
http://www.tirerack.com/tires/tires.jsp?tireMake=Goodyear&tireModel=Wrangler+MT/R+with+Kevlar
...I recall the original MT/R was very close to the same, if you are talking about the older tire.
http://www.tirerack.com/tires/tires.jsp?tireMake=Goodyear&tireModel=Wrangler+MT/R+with+Kevlar
...I recall the original MT/R was very close to the same, if you are talking about the older tire.