Shear stress on a tire from a puddle of water

[Elyk]

Homework Statement

A car is moving at 65 mph and hits a puddle of water 1 inch deep. What is the shear stress on the tire from the puddle of water if the radius of the tire is 16 inches.
r = 16 inches
u = 65 mph
y = 1 inch
mu = viscosity = 2.344*10^-5 lbf*s/ft^2

Homework Equations

angular velocity:
omega = u/r
shear stress from fluid:
tau = mu*u/y

The Attempt at a Solution

Velocity at the bottom of the tire is equal to the velocity of the car:
u = omega * r
shear stress on the tire:
tau = mu*u/y
I'm not sure about the velocity at the bottom of the tire.

 

[gneill]

Presumably the bottom of the tire is in contact with the road surface and not slipping, so its instantaneous velocity will be zero.