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Will I need to bring the Pacifica into the dealer to reflash/reprogram the tire size in the MPH calculations when going from the 17" to 20" wheel/tire package? Is this even an option to get reflashed via dealer?
 

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I don't think so. The outside diameter should be the same. You just get less tire in profile. Don't know about the suspension changes for the heavier unsprung weight though. Probably nothing to worry about.
 

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Discussion Starter #3
Using the tire calculator, it showed a .60" diameter increase from the 17" rim/tire profile. Showing a 2mph difference past 60mph.
 

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Bumping this thread. I'm thinking about going from 20" OEM wheels on a Limited to 17" wheels for snow tires (less expensive and more sidewall). Will the 2 mph difference cause any issues with adaptive cruise, etc.? Is there any setting or dealer option to change the tire size for mph calculations? Thanks.

Using the tire calculator, it showed a .60" diameter increase from the 17" rim/tire profile. Showing a 2mph difference past 60mph.
 

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Bumping this thread. I'm thinking about going from 20" OEM wheels on a Limited to 17" wheels for snow tires (less expensive and more sidewall). Will the 2 mph difference cause any issues with adaptive cruise, etc.? Is there any setting or dealer option to change the tire size for mph calculations? Thanks.
As long as all four tires & wheels are the same size, it won't hurt anything or adversely affect how anything works such as adaptive cruise, ABS, or stability control. The only noticeable difference will be a slight inaccuracy of your speedometer. If you install the alternate OEM size of 235/65/17, your speedometer will indicate roughly 2% faster than you are really traveling according to Discount Tire's size calculator. For example, when your speedometer says 65 MPH, you will really be going 63.6 MPH. That tire size is actually the largest size available (with regard to overall height & circumference) from most manufacturers for 17" wheels. I say this to inform you that there isn't a 17" tire size available that would be a near-perfect match to your current 20" wheels & tires regarding circumference (which directly affects speedometer accuracy).

You could have the dealership recalibrate the ECM for the different tire size, but it's not worth it IMO since the snow tires will only be on temporarily. You'd need to get the ECM calibrated again when the bigger wheels are installed again anyways. Obviously, the dealership won't do this for free.
 
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