The GMC CCKW

The technical term for the steering method your CCKW uses is "Ackerman Steering," a system in wigh the individual front wheels pivot at the knuckles and are connected by a tierod so that the wheels rotate together about their pivots.
The Horse and buggy which the CCKWs had recently replaced used a "fifth wheel" method in which the entire front axle pivoted from a central point.

Here is a good page for understanding the Ackerman principle. You can turn the wheels and see what happens. Do you know the optimum ratio for steering arm angle to wheelbase?
Cheers,
Barry

http://www.compgoparts.com/technical/001/Ackerman.asp

Neat.
The inner wheel turns at a sharper angle to enable the vehicle to turn with the least possible radius. If it were not using the Ackerman Principal, it would take forever to complete a turn.

Thanks Barry, that is interesting.

With this type of steering, if you draw a line thru the center of the two knuckle bearings towards the ground, it will pass through the center of the tire at the point of contact with the ground. If it dod not do this it would be much harder to steer.

I think someone forgot about Caster.

Yes, caster would make the contact point a little forward of the actual point of contact.

It would however still be in the center of the tread. Caster is sometimes called steering axis inclination. That is what keeps the wheels going straight while you are going forward and the same thing that makes the steering wheel want to go to the lock right or left when in reverse.

Without caster the steering would be very difficult and shimmy would be chronic.

The easy way to figure caster is look at bicycle forks. A bicycle has lots of positive (+) caster. You can easily ride a bike with no hands, right?
Now turn the forks around backwards to give you lots of negative (-) caster. Betcha have a brute of a time riding it with no hands now!
Cheers,
Barry

Do I have caster on my Unicycle...

When you assume the caster attitude, on your Unicycle you will be about to fall on your ass. Caster is not a good thing on a Uniclcle. It would be neat to be able to ride one, but I gotta feeling that I should forget the idea.