V-sunk

I ran with Vsync on ever since getting into the beta in June 08 because with it turned off I was getting a bizarre texture squirming that made me dizzy. The top part of the screen would be from one frame, the bottom from an earlier frame, so the whole sense motion was distorted in a very unsettling way.

Vsync cured this. I also set Frames Rendered Ahead in the nVidia Control Panel to 0 to eliminate display and controller lag.

That was with an nVidia 8800GT. Over the winter I got a 9800GTX+ OC, but I kept Vsync on and just cranked up my graphics details. Ah, full shadows! Wonderful!

But I wasn't racing very much and when I was, I felt frustrated. In retrospect, I think this was because I never felt connected to the car; I was always reacting to things that had already happened instead of what was going on right now, and my inputs took a little time to get to the car's physics.

Then Todd Bettenhausen convinced me to turn off Vsync. Suddenly my experience with iRacing was transformed! I felt totally connected to the car. Its responses to my inputs were instant, precise. On road courses I immediately gained a couple of seconds in lap times.

At first I was running with frame rate uncapped. Frame rate was mostly between 150 and 250 FPS. I read that this overworks the video card, so I capped the frame rate at the default 82 FPS. The immediacy went away; I felt disconnected again. So I removed the frame rate cap.

At a few corners on some tracks (Road America, for example) the frame flow got choppy and/or the screen squirming came back, so I turned off shadows. It seems that as long as the frame rate is running above 150 or so, everything is quite smooth and there's no squirming.

I tried the steering wheel test: I turned on the on-screen wheel and got in the car. I turned my G25's wheel back and forth rapidly. With Vsyc off, the wheel on the screen moves in perfect synchronization with the actual wheel.

Then I turned on Vsync and restarted the sim. With Vsync on, there is a very, very noticeable delay. The on-screen wheel's motion lags the real wheel by a significant amount.

I suspect that the video card and driver have an impact on this. Perhaps some (ATI?) cards don't exhibit the same behavior. Perhaps there are other settings in iRacing or in the video card control panel that will minimize the delay with Vsync turned on. (Todd tells me that now he is running with Vsync on, but he's turned off AA and AF in iRacing and instead turned them on in the CP - and that this gives him very minimal lag.)

But as far as I'm concerned, based on my own experience, zero lag trumps everything else. I need that instant response to my control inputs, and I need that instant feedback through the wheel and on the screen. I don't care if I'm overworking my video card. If it cooks itself I'll get a new one.

No more V-sunk for me!

Alison

From a comment on an inRacing forum thread:

http://www.inracingnews.com/iracing-news/v-sunk/