http://www.tirerack.com/tires/Spec.jsp?make=BFGoodrich&model=Rugged+Trail+T%2FA&vehicleSearch=false&fromCompare1=yes&partnum=67R7RUGTTA&tirePageLocQty=%26partnum%3D67R7RUGTTA

not sure if that link will work, but you can go to tirerack dot com and look at specs.

LT tires are around 10 lbs heavier than their matching SL tire.

Ask the dealer where they think that 10 lbs (25% more mass) went, and if htey think a 40 lb tire is as 'tough' as a 50 lb tire of the same external dimensions.