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
Using GPS to drive the spedo/odo on a car seems like it wouldn’t be super reliable?
That’s why it’s not a thing and OP is wrong.
Not so good in a tunnel or surrounded by high rise, trees etc.
A lot of tunnels have GPS beacons to mitigate the issue of constellation blindness.
Can you tell me some tunnels that have GPS?
It becomes reliable if the car uses all the other sensors together with the GPS. Current German cars do that for their internal computers, for positioning, controlling their driving dynamics etc. Such systems are able to drive through several kilometers of tunnels and still know their own position with a deviation less than a meter, and afterwards adjust it again from GPS and mobile antennas etc.
But they usually don’t display this data on the spoedometer.