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.