I doubt that weight distribution makes much difference, although a heavier stoker might slow the rear wear down a little. Tandem rears wear much faster than single rears ridden by the same riders. The issue is the increased torque on the rear wheel because 2 riders are torqueing it, not just one. Tandem fronts also wear faster if they are ridden as fast as a single due to the increased braking force on a tandem and the greater force on both tires in a corner or turn, though front wear is not as obvious as rear wear.
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