Incorrect Speedometer Reading

[SquattingDog]

Originally Posted by Hammer

How did you confirm your speedo is out?

Not sure what it's like in North America but in Australia all speedo readings are optimistic (compared to true road speed). This is simply a liability protection by manufacturers to ensure they don't get blamed for anyone caught speeding (or worse, involved in an accident).

But I'm talking small numbers here (2-6 kph difference) ie. true road speed is slower than what's indicated in the speedo (or HUD).

Plus the 20" staggered wheels have a smaller rolling diameter compared to the 18" or 19". The effect of this is to make the speedo read more optimistically that the true road speed.

There are several remote radar sites that post your speed throughout Charlotte, including one in my neighborhood. I also verified with the Andriod app SpeedView. They all read 2-3 MPH below what my speedometer shows at any speed.

Over the past 10 years, I have owned several GM vehicles and 2 Acuras and I have never noticed an MPH discrepancy. The speedo on my 2010 MDX seems to be exactly accurate from what I can tell.

I also believe that manufacturers calibrate the speedo to reflect the factory wheel/tire package, so wheel/tire sizes should not affect speedo accuracy.