Wheel / speedo re-calibration

[Blk2015GT]

The base GT has 18" wheels. The PP has 19" wheels. I have the 20" wheel option on mine. As the wheel size goes up, tire sidewall goes down. All 3 of the above wheel/tire packages should have the same overall diameter.

This.

If you use standard size tires (sidewall height) for 18/19/20s, 50/40/35, respectively then you wont be off more than 2mph or so. The overall diameter of the tires on the wheels are within tenths of inches of each other.

If you ever get pulled over for 2mph I'd be completely shocked.

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[ElAviator72]

No, it's not that. It's because you're looking at the speedo off angle. For some reason, ford decided not to angle the speedometer toward the driver. If you move your head so that you're dead center in front of the speedometer, it'll likely be "accurate."

Wow, in aviation, Parallax in analog instrument heads is a well known phenomenon. Most cars made in the last 20 years or so are dumbed down enough that it is designed out ;)

 

[RubyRed15]

Has anyone actually gotten a recal at the dealership or is this still just a rumor?

 

[ElAviator72]

Has anyone actually gotten a recal at the dealership or is this still just a rumor?

For what? A miscalibrated speedometer? Haven't heard the rumor about that one...

 

[BeauxXL1200]

Going from the 19" Performance Pack wheels and tires to the monsters now
on the car my speed is off by 2.4 mph as measured with GPS. I am not
worrying about it.

If the speedometer is 2.4 mph faster, does this mean that the odometer is recording slightly more miles than you're actually traveling?

I'm going to upgrade to 20s from my PP 19s, and the total diameter will increase approximately 1/2 inch, which means my speedo will be showing a slightly higher speed than I'm actually going. Which I don't really care about b/c I'll know it's a bit higher.

I just don't want the odometer showing more miles than are actually on the car.

Anybody know?

 

[2015 Silver GT]

Yes your odometer will be affected as well.

 

[BeauxXL1200]

Yes your odometer will be affected as well.

Bummer. Oh well, I don't think it'll be enough to risk taking it back to the dealer to have them try to recalibrate it. They'd probably screw it up or srew something else up.

Thanks. :cheers:

 

[Lakeland-GT]

I'm kind of wondering about my factory calibration...I took my car on a road trip for the first time last week and set the cruise on the interstate. I noticed that the cruise control speed was about 2 MPH lower than the speedo said I was doing...

Same here maybe even 3 mph lower than speedo.

Edit: The error in mph increases as the speed increases (so it's probably a % error issue). Below 50 mph it's negligble. It's about a full needle width at 70 mph (black side to black side, since the needle extends quite a bit beyond the red line on both sides).

 

[GTP]

Did you lean to the right to eliminate the parallax effect?

 

[Lakeland-GT]

Did you lean to the right to eliminate the parallax effect?

Yep, I did the lean over.

 

[B.Crowder]

If the speedometer is 2.4 mph faster, does this mean that the odometer is recording slightly more miles than you're actually traveling?

I'm going to upgrade to 20s from my PP 19s, and the total diameter will increase approximately 1/2 inch, which means my speedo will be showing a slightly higher speed than I'm actually going. Which I don't really care about b/c I'll know it's a bit higher.

I just don't want the odometer showing more miles than are actually on the car.

Anybody know?

Actually, I think a larger diameter wheel would cause the speedometer to show a lower than actual speed (less wheel revolutions per distance travelled with the larger diameter/circumference). Your odometer would therefore show lower than actual mileage.

 

[BeauxXL1200]

Actually, I think a larger diameter wheel would cause the speedometer to show a lower than actual speed (less wheel revolutions per distance travelled with the larger diameter/circumference). Your odometer would therefore show lower than actual mileage.

Now that's something that I can live with. Less miles on the Stang. Woo hoo! :cheers:

 

[Poppacapp]

I'm assuming the car takes the speed reading from the front wheels but can anyone confirm this? My fronts are overall shorter then the rears so I just want to know which wheels to adjust my speed by.

Do a burnout, and watch your speedo climb. Usually a sensor near output shaft of tranny.

 

[Tb8983]

Around my neck of the woods its a $150 bucks to reprogram the speedo

 

[DivineStrike]

Speedometer is measured by the rear wheels, track apps are measured by the front. Different tire height changes the speedometer error by a certain percentage, not a flat rate number. My PP Speedo reads about 4% low. Meaning I am actually getting 4% better gas mileage than indicated, and also a slight extended warranty lol...Not that I'll be using it to it's extent. I will probably tune and mod by 40k.

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