Question 1182045
The onboard computer calculates the linear speed from the 
rotational speed and the assumed radius of the tires
The linear speed is given by v = w*R, where w = the rotational speed, R = the radius
The assumed linear speed = v1 = 65 mph = w*R1, where R1 = the assumed tire radius
The actual speed = v2 = w*R2, where R2 = the actual radius
So the ratio of the speeds is just the ratio of the radii.
v2 = (26.1/2)/(24.3/2)v1 = 1.074*v1 = 1.074*65 = 69.81 mph