Available wheels, tires on new Mustangs and other new Fords

On the 2010 Mustangs and other Ford models, available wheels are: Mustang: 17", 18" and 19" Taurus/SHO: 17", 18", 19", 20"
Flex: 17", 18", 19", 20" Edge: 17", 18", 20", 22"
My question for the day: Unless the larger diameter wheels use lower and lower profile tires to maintain the same overall wheel diameter, is there a mysterious computer "module" that has to be replaced to adjust the speedometer for different sized wheels?
If I were to replace my 17" wheels with 19" wheels, then what?
Just curious, Dick
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dickr2 wrote:

Your dealer has a machine that plugs-in to, and adjusts, your car's computer. Or you might do it with a handheld (SCT or similar).
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Frank ess wrote:

More: if the discrepancy from stock wheel-revolutions-per-mile is less than a percent or two, no adjustment necessary. Your suspicion about aspect ratios is likely correct.
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It depends on the system as to which module has which sensor on it's network branch.. Tire size (or a variation of it) will be an adjustable parameter in "that" module.
At one point, we could pretty much just plug in the appropriate revs per mile info but Ford has started limiting our choices to the factory available sizes in a preset list.
There are aftermarket devices one could use for programming other tire sizes.

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