The tires on our new car have a diameter of D=634.5 mm and a tread depth of d0=8.0 mm. The technician set the car's speedometer to measure accurately for this original wheel size. However, we drive frequently, so after a while, the tire tread came down to the minimum depth for summer use, dmin=1.6 mm. How does the actual speed now differ from the speedometer reading? Give the answer as the ratio of the speed on the speedometer to the actual speed.