It means you're turning it too far. If you turn your wheels to a certain point that is beyond ideal, you're just scrubbing off rubber. The vibration is a way to allow you to sense that it happening. Remembere faster you go, the more sensitive the wheel rotation becomes, so if you find yourself feeling that vibration, that's the physics talking back to you to let you know that you're not helping it turn, you're just turning it too far and scrubbing off rubber. If you find yourself in that situation more times than not, that's likely an indication that your driving techniques need refinement. Guys in my iRacing league used to complain the MX5's tires would crap out on them 5 laps before the end of the race, but it wasn't the tires fault. It was the driver's. Those of us with higher end wheels typically never had that issue. and I explained to them it's because they aren't feeling out the limit of their tires when they're cornering. This problem can present itself in several scenarios. Most of the time, the driver is either; driving too aggressively, causing inability to detect subtle changes in force / build up, etc. Or, they're running lower end wheels like a g27 or the GT force or sidewinder, and their force feedback is set way to high or too low, where there's no progression to turn in, and they're litterally unable to feel a build up of grip, or the limit of grip. Idealy, you always want to feel a sort of "spring" when turning in, and by that I mean the resistance should be peeking right as your tires approach the limit of grip, and hopefully your wheel of choice isn't clipping at this point. It's ok for the wheel to be close to it's peek, but it's better leave headroom and keep the setting at 5 and under for strength, and 4 and under for sensitivity. (I run 5,1) everyone will eventually decide on an ideal setting for ffb. Having a little headroom left over when your tires hit the max grip allows your wheel to dance around a bit while going over bumps as well so keep that in mind. Nothing demonstrates this better than hot lapping on nordschleif. Once you're past that limit of grip though, and try to compensate by turning farther, it'll do you no good, and when you turn it so obsurdly far that the front wheels are essentially driving partially sideways and scraping off enormous amounts of rubber compound, that's when in GT, (in real life too) you'll typically begin to feel stuff through the wheel that you'd otherwise not have. The effect GT Sport uses can feel a bit exaggerated, but that doesn't matter; that effect was implmented for one reason; to let you know "hey, buddy, turning in further ain't gonna help you get through this corner better, so next time estimate your entrance speed better and I won't vibrate and bother ya".
