Saw a truck around town today with a ridiculous lift kit and chunky off-road tires that were clearly much larger than factory standard, and it got me thinking; if you install this kind of modification in a car, do you need to adjust the speedometer to compensate? What about the odometer?
My logic is the only absolute measurement the car has is how fast the wheels and drive shaft are turning, so presumably there is some sort of multiplier - 1 revolution = X meters - that is then used to show speed and track distance travelled, but that factor would need to change if the circumference of the tires did
I don’t think so because the 14" and 15" wheels for the same car should have a different second number to their tire measurement to compensate, the manufacturer wouldn’t recommend installing tires that will make your speedo different depending on your wheel size.
First number is width
Second number is height of the sidewall as a % of the width
Third number is wheel size
So for example my summer tires are 255/45R20, my winter tires are 255/55R18, increasing the sidewalk height from 45% to 55% of the 255mm width compensates for the wheels being 2" smaller
I know, but still the circumference differs. It’s 195/60R15 vs. 185/65R14
Obviously, the 10 % difference are just a feeling.