By Steve Haagen (Radsrh) on Thursday, February 8, 2007 - 11:25 pm:
Danbury you are correct in saying that most cars drive with only one tire, the differential allows the tires to turn at a different speeds for going around a corner. ( inside tire turns slower and the outside faster ) All most all cars have a OPEN diff driving only one tire the power can shift side to side but only one tire at a time. If you ever had a car go into deep mud or snow you would notice that the tire that can free spin will be the drive tire. The diff assumes that the tire is moving the car because of the low resistance so it sends power to that tire. Back in the sixties it was all the rage with muscle cars to get a limited slip or locker so both tires would go up in smoke during a burn out, how many times today do you see just one black line on the road when the teens get mom or dads car out for a spin.
AWD cars and trucks get that term because you can leave them AWD or 2 wheel drive on dry pavement with out doing any damage to the drive train. The way they can stay in AWD on hard dry ground is they use fluid coupling in the drive train just like a automatic trans. You can only generate so much torque with the fluid before it slips, the slipping will not harm the metal drive train parts but will generate a lot of heat. The higher end SUV’s and cars that say they have a front locker is true to some extent, it will drive both front and back tires but the coupling method is a fluid transfer case. Just like a regular AWD car if the torque load gets to high the fluid link will slip to relieve strain on the drive train parts so it can leave you stranded. You also are correct that the 4WD trucks I was talking about where the true 4WD heavy duty type. The locking method used is a metal to hard clutch or spring loaded teeth that will unload to allow the tires to turn a different speed and then relock to drive both tires . In this case you should never run in 4WD on dry pavement for a long period of time and NEVER run it in 4WD low on hard pavement, there is so much torque from the low gearing that one tight turn in 4 low on solid ground can snap a solid metal axle in two at the same time there is so much torque that you can pull a full size truck with or without a trailer up a very steep loose or soft hill with out any trouble.