My steering is set to 900 and the cars wheels stop at about 1/4 of the way to the full lock of 900 so Forza is taking off some of my degrees so that some of my degrees are not being utilized, they just dont do anything. There is no way to fix this as far as I can tell. Also, it may just be the 458 GT3, but the slightest braking and steering input cause the car to spin out.
Sucks, they locked the wheel rotation ingame to 180 degrees, good job.