Say in this ad "not for cars with 20 inch wheels"
Thanks for the researchYes, they physically will fit on front and back but due to difference in diameter, 25.32" vs. 27.3", it is advisable to only use them in the front to prevent damage to the limited slip differential. Thus if you have a flat in the back, mount the spare in the front and move the full size front to the rear.
Doing some more research the base 235/50x18 tire is 27.25" in diameter which contradicts my theory above since the spare is available with the 18" tire/wheel. I wonder if it is related to the 20" originally being a Summer only tire which could result in some strange handling if one of the tires was a donut.