Well i asked about this but i figured out how to do it!I figured alot of other people are in my same situation so im going to tell how to do a skid steer set up for tanks,and other tracked vehicles.

Ok on a skid steer the way it works is when wanting to go left it applys the left side brakes and puts power to the right side.Witch at first i couldnt get to work in 3d rad.But after a little power adjustment i got it to work.
So to do this for your self you will need 2 wheels on each side.

In the settings of the wheels check mark throttle,reverse,and brake(this is for all the wheels there should be 4 or more.

Set throttle and reverse to what you like.In my case i used up arrow for throttle and down arrow for reverse(for both left and right side wheels).

Then set brake's left side wheels to something.I used f8.Then set the right side brakes to something.I used f9.

Play around with brake power and throttle power(reverse should be the same as throttle power).

Now when your playing you throttle up plus press f8(or what your key is) and it will go left and throttle up and press f9 to go right.I hope this helps some one out.It sure did me.

A demo is coming soon.