Speedometer not accurate

[rocsteady]

Can this be done with forscan lite.

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[AZ_Ryan]

So new tires put on, OEM size...speed still off by the same amount. Probably needs to be fixed in ECU by dealer or Forscan.

I think you are chasing your tail here. I've used Forscan to calibrate my speedo and it still shows slow by 1-2 MPH. Few people have been able to get it spot on, and it will change no matter what with tire wear. I think its just a Ford software thing, possibly an every car software thing. If you do a search online, just about everyone (including Mustang owners) say their cars read 1-2 mph slow. The problem is no one noticed until we had these digital speedos. It seems to be the norm.

Also, front tires wont affect the speedo. Its the rears.

 

[AZ_Ryan]

I just tested out my GPS speed at 10 MPH increments from 20mph to 90 mph. My feeling is that its defiantly a Ford programming thing to always over read. From 20-40 MPH my speedometer read 1 MPH slow compared to GPS. From 40-90 MPH my speedometer read 2 MPH slow compared to GPS speed.

If the Tire circumference was incorrect, the MPH difference should have slowly and incrementally changed the faster I went. The fact that there was no change between 40 and 90 MPH tells me its a programing thing. In order to compensate for this, you would have to enter an incorrect smaller value for the tire circumference using Forscan. And that may actually cause it to read too under read at slower speeds. To me its not worth the guess work for 2 MPH.

 

[PKs]

Several years ago I had a tuner experiment with my 18 and he was using HP Tuners program. He said that there is a Euro speedo setting standard of 5 to 6 klm per hour difference to actual speed (which was the case for my car) and there is a US standard of 1 to 3 klm per hour difference. He changed mine to the US which brought the car's speedo to 2 klm per hour overread. This is an acceptable safety margin for me.

 

[GMB Racing]

any digital readout is +- 1 digit depending upon the decoding. so 50.5 Is 51 and 51.49 is also 51.

 

[AZ_Ryan]

any digital readout is +- 1 digit depending upon the decoding. so 50.5 Is 51 and 51.49 is also 51.

No doubt. But in this case Ford's programing seems to be intentionally set so the speedo reads 2-1 mph faster that it really is. It's not just simple rounding.

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