Nick Disjunkt (JIM THE TRUCK Blog) had some trouble with rocks getting stuck in the DUALS, but i cannot find the exact page on his website.
duel: a contest with deadly weapons arranged between two people in order to settle a point of honor. (i.e. nothing to do with tires
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There is also conern of being able to air down a dually tire for several reasons. Firstly, most dually tires are high load range with stiffer than SRW sidewalls, i.e. designed to carry heavy loads or you likely would not need dual rear tires. They do not air down well, the lips are different than normal truck tires and the insides of the tires can actually rub together at low pressure or high loads, causing both tires to fail.
Dually tires are for stability and for heavy loads, not for serious off road work.