For correct rolling wheels we have
to know this basic on circles:

Circumference(C) = 2*pi*Radius(R) ;    

or shorter:   C = 2*pi*R
The Greek sign for Pi ~ 3.14159...
in POV-Ray is simply "pi" (lower case!).

If a wheel rotates once around the axis,
then it will move foreward by the length
of it's circonference C.

If a wheel rotates by an angle Alpha,
the wheel will move forward by
  S = C * Alpha/360 or
S = 2*pi*R*Alpha/360.

On the other hand:
If we want a wheel to move forward by S,
this wheel will rotate during this
movement by an angle of
  Alpha = S*360/C or
  Alpha = S*360/(2*pi*R).

Note: Here all angles were messured in degrees!
We should use capital letters for our variables
to avoid any collision with predefined POV-Ray variables!

Rolling wheel: rolled off circonference (orange) and angle of rotation (green)

If we want to roll a vehicle with wheels with different radii R₁ and R₂
the wheels will rotatate with different speed.
 
While the first wheel with R₁ is turning by an angle of Alpha₁ degrees,
the second wheel with R₂ has to be turned by an angle of Alpha₂ = Alpha₁*R₁/R₂ degrees.

Rolling wheels with different radii.