I used to work in the industry, .
Older speedo's I totally agree with you can be out, hence why UK law generally gave you 10% +/- 3mph.
Modern car's that is simply not the case and is really a Hail Mary defense. 99% of the speedos are balls on accurate.
The ONLY time they are out is IF you decide to change the rims and wheel size, that is the only time.
YES I will concede that there is a "chance" your speedo will be out, but in reality no.
The speedo gets it's reading from a Wheel Speed Sensor (initially) this along with other sensors feeds into the OBD, it's all digital.
The speedo itself has solid state electronics and a self test device, when its tested in factory, it is confirmed by computer by feeding a signal into
it is pure maths, a signal of a certain frequency deflects the needle a certain degree, there is no calibration, it either is or isnt.
The speedo itself and the needle reads off the speed, the needle is also set to zero and max, now during testing if it fails any test, the speedo is NOT repaired
it's not calibrated, it's sent back. The speedo is also tested after installation into the car again by computer, which can detect issues.
Older speedo needles had a spring, which is where you could get your inaccuracies
As I said of course they still can go faulty, but it is MORE common for a speedo to stop working through a faulty sensor or instrument itself rather than go "out" of
calibration.
Not saying you can't use it as a defense, it's just highly implausible that the speedo is out of wack, it just doesn't happen.
With all due respect
jsherk wrote:Speedometers are no longer mechanical devices, and are completely electronic nowadays, even if the needle itself is still a physical needle as opposed to a digital readout.
They use a sensor either on the transmission or a wheel.
As with all electronic devices, the speedometer is not guaranteed to be accurate UNLESS you have properly calibrated it against a known standard.
I can not find any requirement in Canadian car manufacturing standards that ever require them to calibrate their speedometers before they sell them to you.
Speedometers are definitely NOT accurate at all.