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My car has the 16" rims on it and in researching tires on my car, apparently the tires that came on my car from the factory were 205-50-16.

The PO put a brand new set of 205-55-16 tires on my car prior to selling it to me.

How do I go about calibrating the speedometer to account for the difference in the tires?

I found an app that measures speed and it looks like I'm off about 2mph at 70mph.

Do you think it's worth it to bother having it calibrated?
 

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Vince your Moderator
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And, NO x's 2
 

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2004 Focus Wagon, Zetec DOHC, Auto
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I am running 205/55-16 size and love 'em. Much better look, ride, braking, etc.

The speedo is off a little and I just keep that in mind while driving. You also have to keep it in mind when doing MPG calculations.

At 70 MPH on the speedo, you are actually going approx. 72.35 MPH.
At 35 MPH on the speedo, you are actually going approx. 36.17 MPH.

Multiply any MPG calculation by 1.034 because you will be off by 3.4%.
 

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My 07 reads 2mph high with stock size tires on it. Nothing is dead-on from the factory but I think Ford (any many car makers) make the speedo run just a tad high to fool us into driving slower than we want. I run a ScangaugeII and the computer knows I'm doing 60mph but the needle on the gauge is in the middle of the 60 and 65 hash marks.

So yea...not worth the cost of recalibrating the stock gauge. Use a GPS phone app or if you have an OBD2 gauge like my ScangaugeII you can tell it to adjust the speed reading when changing tire sizes.
 

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2004 Focus Wagon, Zetec DOHC, Auto
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Nothing is dead-on from the factory but I think Ford (any many car makers) make the speedo run just a tad high to fool us into driving slower than we want.
I guess it is just the luck of the draw or something because my speedo was dead on when compared to what my GPS said. The variances I had were from tire wear (new vs. shot).

After changing tire size, the GPS now agrees with calculated speeds instead of the speedo.
 
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