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Discussion Starter #1
So I recently bought an 06 charger SXT. It came with stock wheels that are 17 inch and has 215/65/r17 tires on it. I bought 20 inch rims for it but they came with tires that a 245/35/zr20. The 20 inch rims with the tires mounted appear to be in total an inch and a half smaller than the stock rims and tires. I've been told this can affect your speedometer and tachometer. How mu h of a difference will this make and how much does it cost on average to have your cars system adjusted to smaller tires? If it costs a ton of money then what size tires do I need ??? Any help would be appreciated on this.
 

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It's actually not a huge difference.

The 20" wheel/tire setup will be 1.2" smaller in diameter, and at 70mph on your speedometer you will only be doing 67mph.

Plug the numbers in this tire size conversion tool:

http://tire-size-conversion.com/tire-size-comparison/
 

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Discussion Starter #3
Ok great so I don't really need to reprogram it or get new tires. Good news I've been anxious to get them on and they're going for a fresh powder coat tomorrow.
 

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It looks like somebody messed up the tire size. The correct size should have been 245/45/20. At any case, if you have a predator or an intune, you can calibrate the speedometer yourself by plugging in the tire size numbers.
 
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