How do I get WheelColliders with 100% friction?

I literally want no slipping at all. The values for WheelCollider make no sense to me, and tinkering around with them at runtime has not made them any clearer.

How do I turn off all slippage and have 100% friction?

Thanks

What are you trying to achieve by 100% friction?

Are you trying to make it behave like it is on rails like a train? If that is the case then the WheelCollider may not be what you want to use. The WheelCollider is meant to simulate how wheels of a vehicle would behave which means that no matter how much friction you give the wheels at the end of the day they are still just sitting on the ground. Which means they can and will slide given enough force.
However with a train you could consider it to be “attached” to the ground as it will only travel on the train tracks.

If you want to achieve motion like a train (but without needing train tracks) you might be better off just correcting the velocity of your object in FixedUpdate.

So by that I mean adjusting the direction of the current velocity to point in the direction you want. If your velocity is always in the direction you want to travel there is no slippage.
By correcting the velocity each frame you are effectively stripping out the slippage.