Turning torque

[Juggernaut]

At work I am working on designing a swerve drive for a fairly large vehicle. I am attempting to calculate the torque needed to rotate the wheel of a swerve drive to make sure I have enough torque from my steering motor.

I have a 4" wide 8" diameter wheel. There is 1500lbs of load on this wheel. The total contact area under this load is .002in^2. The coefficient of friction for the wheel and the surface it will be running on is. 0.5.

If anyone could point me in the right direction to be able to figure this out it would be greatly appreciated.