Anyone else notice that their speedometer is off with factory tires?

[puckett_jw]

I have been feeling that I was driving a little slower than what the speedometer was saying. I used a GPS tracker to see that I am running about 62 when the speedometer says 65. At this time I have not made any changes. I do have SAS, so I was wondering if they did something wrong at the factory. Are any of you noticing a similar issue?

I know that you can use Forescan to adjust the setting, but I have just not gone there yet.

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[AMTRV]

Mine is right on.

 

[L8apex]

Most factory speedometers overpredict by ~3%. It’s by design.

But note in the drive by wire world this does not over express on your odometer.

 

[Tricky Dick]

Yes my BL said 60 while the real speed was 58.

 

[MayhemMike]

Wow, I have been claiming this since I took delivery. I have not compared my speedometer reading to a gps , but I believe the speedometer is showing a higher speed then the actual speed.

 

[Denny3297]

Yes! My Badlands Sasquatch is off by the same amount!

 

[RedDawg]

Well whadda ya’ know!!
I drive by two different radar signs daily and they both have me slower than my speedo.
I thought they were off!!

 

[cowman]

Slow by 1 mph...

 

[Ducati1098]

Yep, factory setting for SAS is only 33.25 inches diameter.

 

[Jhuff]

Do you guys have fairly new tires? This should be normal then.

Based on what I've seen, and from discussions in the Forscan threads (for adjusting tire sizes), the computer is set for a tire circumference smaller than what actually exists when new.

This way, the MPH/MPG isnt way off when your tires are worn (having lost over an inch of diameter).

 

[Shotsy]

Do you guys have fairly new tires? This should be normal then.

Based on what I've seen, and from discussions in the Forscan threads (for adjusting tire sizes), the computer is set for a tire circumference smaller than what actually exists when new.

This way, the MPH/MPG isnt way off when your tires are worn (having lost over an inch of diameter).

THIS 100%

I figure the offset is the AVERAGE circumference of new vs. tires with maximum tread wear.

 

[Jofenech]

I remember reading somewhere that a Speedo intentionally overstates for liability reasons, if it understated and you were pulled over for speeding you could blame the vehicle, much less in an accident.

 

[tongsun3717]

When I replaced tires from 255/70/R16 to 285/70/R17, I calibrated the speedometer with a Garmin GPS. After a 5835 miles trip, I believe it is right on, with 2508 for the peripheral.

If one calculates the peripheral of a tire according to the parameters, the tire diameter is not the effective diameter under load. A 3-4% error is typical, depending on the pumped PSI.

 

[WuNgUn]

2% mine were out, Squatch Badlands. I fixed it with Forscan...
For reference, 2600mm is what you want the BCM entry to be

 

[puckett_jw]

So here is the funny part of this....

The first time that my wife drove the new Bronco was following me home after I picked up the new F250 Tremor. She kept lagging behind. I was just assuming that she was nervous driving the new Bronco. Well, when we got home, I got an ear full about leaving her behind & such (in a loving wife sort-of-way). I was like wait, what did I do wrong. I checked my new truck & it is spot on. She was not having any part of it being an issue with the speedometer, so we checked it on the way home together after church the other day & what do you know--it WAS off. I did not dare say I told you so, but it was written all over my face ;-).

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