Question

16. If the factory installed tires of a car have a circumference of 98.5 in. and you change them to new tires witha circumference of 110.9in, and didn't calibrate your tires, what would your actual speed be if your speedometertold you that you were driving 50 mph in a 55 mph zone? Are you speeding or actually going under the speedlimit?

Answer 1

The circumference of a circle is given by:

`C=\pi\ast d`

In which d is the diameter.

Old circumference:

98.5 in

New circumference:

110.9 in

Increase:

We have to find a value x for which:

98.5x = 110.9

So

x = 110.9/98.5

x = 1.1259

The new tire circumference is 1.1259 times the original. This means that the true speed will be 1.1259 times the speedometer.

We have that:

The speedometer is 50 mph.

1.1259*50 = 56.3 mph

Your actual speed would be of 56.3 mph, which would be above the speedometer.