In the past, when I configured my video each time I upgraded my system, I made sure to check-off the box for V-Sync under the graphics options because the resulting effect on the sim was quite smooth and produced the best moving image quality with little or no stutters or “artifacts”.

So I have been quite happy with this and what I would describe as intermediate settings (no shadows) on an intermediate quality video card and CPU/motherboard. But although the graphics quality is more than sufficient for my needs I have plateaued in my driving skills, which I always blame on lack of available time to devote to practice and improvement.

My kingdom for an apex.

My kingdom for an apex.

But after reading a couple of recent forum threads related to graphics settings (specifically V-sync) and input lag, I was curious if it would have any affect on my system and my limited control skills. The V-sync is a graphics setting which locks the graphics card into a pace which matches the refresh rate of the monitor, so the resulting stream of images progresses in a controlled pattern and the result is a quite smooth transition from frame to frame, which is pleasing to the eye. When the graphics are not V-sync’ed you can allow the graphics card to run unlimited, allowing it to generate as many frames as it can (but which are only displayed at the rate of the monitor refresh, so several frames are drawn by the card but not displayed), or you can cap the graphics card at a certain frames per second (fps) rate, defaulted at 83. Often, the result of capped or unlimited settings is a variable number of dropped frames, leaving the rate of change of the view to vary from frame to frame apparent to the viewer. As a result the scene flows in a much less smooth sequence and is generally less pleasing to the eye. Some even report eyestrain problems when running with V-sync off.

I decided to run a quick test to determine if V-sync settings played any role in my driving performance. When V-sync was on I noticed a barely perceptible lag between the time of my inputs (turning the wheel or applying pedals) and the resulting change in the inputs displayed on the screen. I figured the latency time was observable but not significant enough to play a role in my driving experience. So I took out the new Corvette C6.R – a car I am pretty unfamiliar with – to a test at Watkins Glen (Boot) – a track I am pretty unfamiliar with – and could only manage to set a time just under the 107% of the world record after about 12 laps with quite a few spins. Then I turned off the V-sync and limited the card to 83 fps, and noticed the lack of smoothness of the flow, but was able to mostly ignore it.  I also noticed that the wheel appeared to have no noticeable lag between my inputs and the on-screen wheel response. I also found that my control was much better and though I was in hot-lap mode I made much fewer mistakes and got my personal best time down my almost a two and a half seconds (104.5% off the world record) on my eleventh lap. I repeated the test with V-sync on and spun quite a bit more and struggled to get within a second and a half of the V-sync off time after 12 laps. Scott Husted reported an almost identical experience in his tests with and without V-sync, and many others have confirmed the same thing.

I'm sensing a lack of grip.

I'm sensing a lack of grip.

This was quite an eye-opener for me.  I didn’t think the lag was that bad to begin with, but once it was reduced I noticed that I had much better control over the car and was able to catch potential spins with much more ease and confidence compared to when V-sync was enabled. I am going to follow-up with a more fair and extensive test to try to better characterize the latency and attempt to quantify how my graphics settings affect it and whether it plays a role in the validity of my past performance excuses.

But in the end it comes down to driver preference and some cannot bear to shut off the V-sync setting due to the loss of smoothness. Some will not have any change in the input latency with changes of this nature as it is very system-specific. However, at this point I highly recommend trying to drive without it enabled to see if it improves your sense of control, whether or not you can notice the input lag.

My only trouble is I have to find some new excuses for being so far off the pace, because it surely can’t be due to my skills. Ahem.

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I’m really more comfortable with vsync tuned on, but I will try more extensively turning it off: I’m curious about it.

Fabrizio Cuttin
November 18th, 2009 at 2:28 am

They shouldn’t stop pooling the inputs and stop ticking the physics while the graphics engine wait for the v-sync. They need to better parallelise their game engine.

November 21st, 2009 at 1:24 am

I think you made the wrong approach to this, you should have tested on a track you are VERY familiar with and a car you are VERY familiar with. Off-course you are likely to pickup time when you continue to make laps on a track as you become more and more familiar with it.

November 21st, 2009 at 7:29 am

So much of this i psychological – do a double-blind test if you actually want to do a relevant test :)

That being said, iRacing does feel a lot different at 150fps vs. 60fps, vsynced or not – and racing games don’t really suffer from tearing in the way that e.g. shooters do.

December 22nd, 2009 at 10:45 am

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 Hine
December 30th, 2009 at 5:54 pm


Thanks for your comments. Yes, that was exactly my experience too. I didn’t believe I had a lag problem until it was eliminated by turning off V-sync and I think that could have saved me from a lot of spins.

I have a new 5850 card now, but before I install it I am going to tinker with settings and see if I can learn a little more about what has the greatest effect on lag.

Ray Bryden
December 30th, 2009 at 7:22 pm

I’ve discovered that although there is no possibility to set limit above 84 fps in game menu, you can actually set it manually in .My DocumentsiRacingrenderer.ini file:
Those two lines should practically eliminate lag and make constant fps which is I believe better solution than just vsync off with variable framerate.
169 fps is the max limit fps you can set, everything above will be cut down to 169, but you can set any frame rate below, maybe 150FPS which is 2,5x of standard LCD refresh rate would be better for you so I will be thankful for your feedback.

February 13th, 2010 at 8:18 am

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February 14th, 2010 at 12:02 pm

I’ve never used v-sync. Not for iRacing, and not for any games or other sims I play. For this exact reason. I just feel like I have more control over the situation and my response time is better.

Justin Weisel
March 8th, 2010 at 8:39 pm

Even with FPSs limited at 60, the “under water” sight I ahve cause the VSync in off is simply not tolerable to me :-(

I have an AMD Athlon X2 with 2.9 each core and an ATI 4850 of 512MB

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December 14th, 2010 at 1:18 am

The trick is to limit the framerate to a multiple of your monitor’s refreshrate.
V-sync serverely increases input polling interval, which is what causes the lag. Running iRacing uncapped is the best way to combat input lag, but can introduce off-putting image faults when refreshrate and framerate are running very out of sync.
I’m running a 200cm projector image myself and image tearing is a huge problem on such a large image. I used v-sync for years until a freind showed me just how much input lag is introduced! Intolerable!
Make sure you install a framerate limit which is a multiple of the refreshrate, and verify that your system is able to maintain this rate most of the time.
Most screens use 60Hz nowadays, so 120fps is a good place to start.
Using 60fps would be about as bad as using v-sync! More is better in this case and, if you can, use 180fps. There is less of a chance that refresh and framerate are out of sync because at 180fps the frames last a lot shorter. I am using 180fps myself. It produces virtually no noticable tearing while, like Alison and Ray, I feel much more connected to the car.

The best of both worlds!

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