Speedometer reads high

[RJ'sGottaDrive]

I've verified this by 2 different methods and my speedometer reads 3-4 mph high.

One possibility I've explored is the difference between 17" tires and 18" tires.

I compared the two and at most, the difference is 1mph.

Anyone have this issue? Is there a way to recalibrate the speedometer?

 

 

'

[rogerjohnsen]

Yes indeed - both my Boxster S and 911 Turbo have the same thing. About 3 MPH over actual speed. I took it into my dealer to fix and was told they had to be within 5 MPH - anything over / under they would fix. So I’ve just dealt with it. In my case it had nothing to do with tire size - all stock. I could see where that would affect it as well but a larger diameter would reduce the speed reading. I’ve just accepted probably all Porsche models around this period read higher than actual speed. 

[JFP in PA]

In reality, All north american cars read high by as much as 5 MPH.

[DBJoe996]

From my understanding, cars are made like that.  My digital and analog speedometer is consistently exactly 4 MPH faster than actual road speed.  Confirmed by many roadside radars.  I just adapt.

Edited October 28, 2019 by DBJoe996

[JFP in PA]

The manufacturer's set the speedo high for two reasons: First, to keep from being sued if you get a ticket for speeding the speed is reading low; second, to run out your warranty faster.  And if you don't think the second is true, there was a class action suit by Honda owners after a TSB stating that was leaked to the public...………….

[RJ'sGottaDrive]

Thanks for all the replies. Out of all the many cars I've owned, the speed difference on this one is the biggest.