While there are a few forum members that have done it, there are a few that will also tell you it led to catastrophic accidents with their cars. More than one XFire with 20" wheels has ended up totalled due to some strange failure.
One of these accidents is being discussed here now. Boiler had his end up upside down in a creek. While he can't say for sure it was the wheel, he also has stated he will never do 20's again.