I attended the SEMA show in Vegas 2 weeks ago and had a chance to talk with the head of 300 development. He is responsible for everything about the 300. I was walking the show floor prior to opening and ran into him while he was setting up the Hurst 300C Special. What a beauty. The car had 22 inch rims and some wide looking tires.
I own a Dodge Magnum SXT with 17' rims and had purchased a set of RT 18' rims and tires. I asked my original dealer before purchase if they could be calibrated for my car and they said yes. My dealer in town did not have what I wanted so, I purchased the car at another dealer.
To make a long story short, I went to my dealer in town and they told me to "GET THOSE RIMS OFF AND PUT THE 17's BACK ON. The warranty will be voided." There are upwards of 20 computers that had to be flashed and the software has not been released to the dealers yet to do this modification. All aspects with the handling will be affected, bad. I did as I was told.
Back to SEMA, I asked the head of 300 development if this was true about not being able to change rim and tire size. He flatly stated YES, you should NOT change anything and the 2nd dealer was correct. The handling is greatly affected. He also said that Chrysler/Dodge is very worried about all the tire/rim modifications being done and that there is no quick fix available. I asked him about the setup on the Hurst 300C and he said that Chrysler has not yet been able to calibrate that setup. They hope to be able to do it and release the car with the same or similar setup.
Careful, these cars are not your cars or old. Don't shot the messenger. Anyone need a set of RT Magnum rims and tires?