Originally Posted by samnelso

Mark the servo horn relative to the case and see if it's turning the same amount when steered by the radio or manually. We can't tell by the pictures, so you're going to have to look at that yourself. EDIT: although looking again at the pics it seems like the servo has a limited steering (dual) rate.

It's either the steering rate as previously described, or just the kinematics of the linkages as they get to full lock. Around full lock the linkages lose stability as the tie rod begins to intersect the kingpin. It's hard for the servo to control at this point as there is no mechanical advantage. Hence, possibly you can turn the wheels farther by hand than the servo would if you're grabbing the tire. Nevertheless, if you have the same rig as your buddy (and built the same) and if this is happening on your other car, it seems to point towards radio settings. I recommend spending a little time in the manual to familiarize yourself with the radio.