Re: Will 20x4.5 wheels fit a roadster?
Advice: The stock wheels are over twice that wide. Installing sich a shallow wheel would not only look very silly, but could very well destroy handling characteristics and make finding tires that fit very hard/expensive. In all seriousness, I believe the size of the wheel has been misrepresented. I have never heard of such a skinny wheel especially in a 20" diameter.
Some things you should know:
The wheels/tires on a crossfire are staggered and the front/rear tires are different diameters. The tallest "sensible" (if you can call it that) wheel size for the front is 19" (rear 20"). The reason for this is installation of a practically proportionate tire onto a larger diameter wheel would contact suspension components in the front of the crossfire (not to mention screwing up everything from your speedometer to ABS).
Some people argue you can modify the components to make more room for the tire. I suggest NOT doing so because of the risks associated with high speed tire failure (tire diameter grows in the center due to centripedal force, contacts suspension componants, blowout occurs, driver dies in a firery highspeed crash). Not to mention the usual problems associated with VERY low profile tires.
Want a reccomendation for larger wheels? 20x10 rear, 19x9 Front. And don't go over 3% difference from the stock tire diameter with your new setup. You will find the ride rough, potholes even more dangerous, and tires even MORE expensive.
Not to mention most 20" wheels look like "ghetto bling bling" more than euro sport car.
Good luck.