I’ve no idea how true it is but I’ve read that vehicle speedometers aren’t 100% accurate, so one vehicle going a displayed 30mph might be going the same speed as another vehicle displayed at 35mph.
There’s probably some leeway built into the system to cover inaccuracies like that, as well as in the cameras own speed detection ability
I’ve definitely went by those speed display signs that say slow down and show your speed and they’ve been wrong quite often by upwards of 5-10mph.
your speedometer is calibrated to a specific wheel diameter and is unaware of changes due to tire pressure, wear, using different tires (i.e. winter vs summer tires) etc. All it “knows” is that the vehicle travels x meters per wheel revolution, but that x constantly changes.
This also means your odometer will be off by some margin, and should really only be used as a ballpark value.
Most manufacturers deliberately include an error on the speedo so they report 5km/h high (about 3mph). My two cars have 2km/h and 3km/h errors
You can look up the speedometer error for most cars, you can test your own using a stopwatch and a measured distance and maths, or a GPS that shows speed to one decimal place. I use GPS essentials
I’ve no idea how true it is but I’ve read that vehicle speedometers aren’t 100% accurate, so one vehicle going a displayed 30mph might be going the same speed as another vehicle displayed at 35mph.
There’s probably some leeway built into the system to cover inaccuracies like that, as well as in the cameras own speed detection ability
I’ve definitely went by those speed display signs that say slow down and show your speed and they’ve been wrong quite often by upwards of 5-10mph.
your speedometer is calibrated to a specific wheel diameter and is unaware of changes due to tire pressure, wear, using different tires (i.e. winter vs summer tires) etc. All it “knows” is that the vehicle travels x meters per wheel revolution, but that x constantly changes.
This also means your odometer will be off by some margin, and should really only be used as a ballpark value.
Most manufacturers deliberately include an error on the speedo so they report 5km/h high (about 3mph). My two cars have 2km/h and 3km/h errors
You can look up the speedometer error for most cars, you can test your own using a stopwatch and a measured distance and maths, or a GPS that shows speed to one decimal place. I use GPS essentials
GPS speed is very accurate.