Why does the rear end slide in the snow and no other time?
Rear end wants to come around in even the slightest snow. Even at like 20mph. What could cause this? It has good tires.
Its a basic answer. Snow's molecular properties are varied many different directions Depending on the snows condition. It the Snow is whet, Its molecules are more malleable hence why it is the ideal snow for snowmen and snowball fights. When Snow is "dry" its molecular setup is more structured so it doesn't want to change. So when driving over snow the snow is like a layer of separate concrete in between your tires and the asphalt, and since snow is slippery, the car isn't moving always, sometimes it is but mostly it is the snow that is moving on the asphalt that makes you back end slip out because you front wheels have control, you back wheels are just sitting their. All of this is why trucks but chains on their wheels. Since a metal chain's molecular setup is more solid than snow, the chain can break through the snow and give you more traction because you are touch the actual asphalt instead of the slippery, no friction snow. So Over all the basic answer would be snow doesn't give on as much friction as asphalt.
to be honest that guys answer was not basic at all and really is not the problem, the reason your geting the rear end wandering on you is because while you have 4wd there is still more weight at the fron of the car than the back and that is what gives the car better traction up front, now it may be worse if you have an automatic transmission because Subaru automatics instead of having a split of torque 50 percent to the front and 50 percent to the rear wheels like Subaru's manual transmissions, the auto's use a 90 percent front 10 percent rear torque split causeing it to drive more like a FWD car than a full time AWD car. My suggestion in either case is to get some good all season or snow tire if you have only a highway tire on now, and don't get on the gas too much and make sure your E-brake is not locking at all.
As Nick previously answered the automatic Outbacks are even more apt to slide its rear on corners when driving in the snow. I did notice this occurance happening to me in my previous truck a 97 Toyota Tacoma 4x4 and to counteract this problem I added weights in the back of the Tacoma, as with the Outback I just placed an 80lb. bag of sand on the cargo area and it seem to help providing you are not driving the car like a rally race, and yeah a good set of snows like General Altimax Artic which I am currently using helps.
I agree with jtablan I also have the General Altimax Artic tires I live in New England and we get a lot of snow these tires are great
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