The Holden is meant to have 195/65R15 tyres.

However when I purchased my Holden it had 195/60R15 tyres.

Because the rolling diameteris different this has affected the speedometer and odometer accuracy. Determine the rolling diameter of each tyre and determine the equation thatrelates the true speed with the displayed speed.

FYI: The tyre size W/P R I means the tyre has a width of W in millimetres(the width of the part of the tyre tread), it has a profile or aspect ratio ofP percent (the distance from the rim to the tread divided by the width ex-pressed as a percentage) and an rim size of I inches (note 1 inch equals 2.54cm).

any help would be great thanks very much! so sure how to even start