Step 1: Fix the geometry of the contact patch.
The tyre print is taken as a circle whose diameter equals the nominal tyre width of 160 mm, so the radius of the contact patch is \( r = 80 \text{mm} \). The kingpin axis sits offset from the wheel centre by \( e = 10 \text{mm} \).
Step 2: Find the effective radius for spin resistance over a circular patch.
When a wheel pivots about the kingpin while stationary, every element of the circular contact area resists rotation with a friction force proportional to its distance from the patch centre. The characteristic radius that represents this distributed resistance for a full circle works out to \( r/\sqrt{2} \), so here it is \( 80/\sqrt{2} = 56.57 \text{mm} \), and squared this gives \( r^2/2 = 3200 \ \text{mm}^2 \).
Step 3: Combine the offset and the spin resistance term.
The kingpin offset and the spin resistance act as two independent contributors to the resisting torque, so they combine as \( \sqrt{e^2 + r^2/2} = \sqrt{100 + 3200} = \sqrt{3300} \ \text{mm} \).
Step 4: Attach load and friction, and check units.
The kingpin torque is \( T = W \mu \sqrt{3300} \). Since W is in kN and the length term is in mm, the product kN times mm already equals N.m directly (1 kN x 1 mm = 1000 N x 0.001 m = 1 N.m), so no extra scaling factor of 1000 is needed, which rules out the options carrying a division by 1000.
\[ \boxed{W\mu\sqrt{3300}} \]