I'm having what feels like a few hundred ms input delay in Forza Horizons 3. My graphic settings defaulted do medium.
Changing it to 60fps may workaround the issue, but introduces others (stuttering, and frame rate dips below 30FPS). On my AMD R9 290 card, I've found that disabling shader cache and/or 'surface format optimisation' in the AMD Catalyst / settings app seems to reduce the input lag, but I didn't have time to test it much (11pm last night). I remember some old config tools had the option for "Max prerendered frames" for the GPU, and given that the 30hz mode is supposed to set 33ms 'frame pacing' I wonder if that could be a fix..
For the record I'm running a 2500k CPU (4.5ghz) with 8GB RAM and SSD.
If you have a laptop with Optimus, take a look at the solution mentioned in this YouTube video:
Essentially, go into the Device Manager and disable the Intel iGPU. The Windows desktop will freak out a little bit, but the game should run smoothly and without any input lag in 1080p. Otherwise, bumping down the resolution to 900p is enough to eliminate any lag.