Hey guys, I was changing my oil today and forgot to loosen the front tire lug nuts before i lifted it off the ground and put it on jack stands. I thought no biggie because the car is in park, so the wheels should not spin. But they do, both of the front tires free spin while the car was put on jack stands and was set in park. Why is this so???

 

Because of the differental. When you take a turn while driving, the tire on the outside of the turn has to travel faster and a longer distance than the inboard tire does. the differental is part of the final drive of the transmission that allows this so you wont get tire hop. When you put the transmission in park you lock up the final drive. But, there is a set of spider gears in the differental that allow the speed difference during the turns.

 

One will spin forward and one will spin in reverse. The car will stay stationary when both wheels touch the ground because one obviously can't spin backwards. If you jack up one side of the car with it in park, it will roll as if in neutral with the tire off the ground spinning the opposite direction as the tire on the ground. A limited slip will help this. Not sure on the TLs but the one in my GN is tight enough that I can jack up one side and loosen the lugs without setting the e-brake.

 

Because of the differential. When you take a turn while driving, the tire on the outside of the turn has to travel faster and a longer distance than the inboard tire does. the differential is part of the final drive of the transmission that allows this so you wont get tire hop. When you put the transmission in park you lock up the final drive. But, there is a set of spider gears in the differential that allow the speed difference during the turns.
Your tireswill turn when they are both off the ground but they will turn in opposite directions (because of the spider gears in the differental). Try to spin both tires in the same direction with your hands and you cant because the transmission is in park
I hope my explanition is ok if not check this out
http://en.wikipedia.org/wiki/Differential_(mechanics)