Where does the speedometer on our cars read from?

I'm doing the LED conversion on my gauge cluster so I'll have to recalibrate my needles when I'm done. I don't have cruise control so trying to set them while driving on the freeway seems even more dangerous.

If the Z reads from the rear wheels or tranny I was thinking I could take off the rear wheels, support the car VERY securely and just run it in place. Should be pretty easy to calibrate against the digital speedo then.

 

Didn't think it was possible to adjust the stock speedometer. What are you planning to use, or are you talking about just physically placing the needles?

 

No I have to remove the needles to replace the gauge faces and LEDs in the cluster. When you put everything back together you need to recalibrate all the needles. The general method of doing this for the speedometer is to put your car in cruise control on the freeway and push the needle back on to the gauge cluster so it reads the correct speed.

 

Not sure if running the car on jack stands is a great idea either. An empty highway might be the best.

There is a lot of rotational inertia in the wheels. Brakes will have a tendency to stop the wheels violently even when pressed extremely lightly, they are meant to stop a ~3400 lb car.

You would need to be careful to not throw the car off the jack stands when accelerating or braking. Should be doable but also not very safe.

 

The wheels would be off and rotors bolted down