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Locking differential

     Following the thread on locking your differential...
     This may be a fine point, but locking your differential does not 
     increase your traction per se. Locked differentials just re-distribute 
     the power (torque) to the locked wheels.
     For example, say you have one wheel on hard ground, an the other on 
     snow. Differential is unlocked. The torque available to move your 
     vehicle is limited by the capacity (traction) of the wheel on the 
     snow. If you have 500 ft. lbs. or torque available to the rear wheels, 
     but the snow wheel breaks free after 100 ft. lbs, what you have is a 
     maximum of 200 ft. lbs to move your vehicle: 100 ft lbs at each wheel.
     Now you lock your differential. The snow wheel still gets it's 100 ft. 
     lbs, but the other wheel gets the remaining 400 ft. lbs. You now get 
     all 500 ft. lbs. or torque available to move your vehicle. Provided 
     the hard ground provides enough traction, (can handle the 400 ft. 
     lbs.) your vehicle will move.
     In conditions where both wheels are on a good quality surface, a 
     locked differential is basically unnecessary. By the same token, if 
     both wheels are on equally poor surfaces, such as ice, a locked 
     differential will not be of any help; the friction coefficient is so 
     low that both wheels would spin, locked or not. Wheels must have 
     dissimilar surfaces for a locking differential to be of significant 
     Jerry Fields