Spedometer

[Newsa]

My ESC light didn't light or flash. And didn't detect any brakes applied. But let off the throttle.
Thus, I thought maybe it only applies brakes per axle. When cornering or shortly after cornering and spinning, ESC activates

 

[Loren]

Nitpicking

Newsa,

For the purposes of answering your question about tire rolling diameter it doesn't matter where the speedometer input comes from, although it does matter if you want to know if the speedometer will measure rear-wheel spin. As you have discovered, if you change tire rolling diameter your speedometer reading will be different from the actual speed (assuming it was correct to begin with) no matter where it gets its input.

Tire manufacturers publish data on revolutions per mile for their various tires. I have found it on the manufacturers' websites. You can compare the original tire data to the new tire data and get a very good estimate of the change you will see on your speedometer.

I prefer to compare my speedometer reading to the vehicle speed as shown by my GPS. This will work on a level, straight road, preferably at a constant speed. I have found GPS speed to be very accurate. If you provide a dealer with the speedometer reading and the actual (GPS) speed he should be able to program a correction very easily. Of course, this doesn't mean that he won't charge you an arm and a leg anyway.

Good luck getting your speedometer calibrated.
-- Loren