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Question 1159089: Your car’s speedometer is geared to accurately give your speed using a certain tire size: 15” diameter wheels (the metal part) and 4.35” tires (the rubber part).
(a) If your car's instruments are properly calibrated, how many times should your tire rotate per second if you are travelling at 55 mi/hr?
rotations =
(b) You buy new 5.25” tires and drive at a constant speed of 60 mph (according to your car’s instrument). However, a cop stops you and claims that you were speeding. How fast did the radar gun clock you moving?
actual speed =
mph
(c) Then you replace your tires with 3.6” tires. When your speedometer reads 25 mph, how fast are you really moving?
actual speed =
mph
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! 55 mi/hr is 80.6667 ft/sec
C=pi*d
if the diameter is 23.70 inches (2 rubber parts and the wheel), then the circumference of the tire is 74.45 inches or 6.205 feet
That would make 13.00 rev/sec for 55 mph or 60/55 *13=14.18 rev/sec at 60 mph
5.25 inch tires have a diameter of 25.5 inches and a circumference of 80.11 inches or 6.676 feet
At 14.18 rev/sec, one is now going 94.678 ft/sec or 64.55 mph or 65 mph rounded
3.6 inch tires now have a diameter 22.2 inches or 69.74 inches circumference or 5.812 feet
13 rev/sec for 55 mph or 5.909 rev/sec for 25 mph
with these new tires, 5.812*5.909 is 34.34 ft/sec or 23.42 mph
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