If you do feel motion - sick while racing in the Rift, try disabling VSYNC in the iRacing options menu. (pcworld.com)
Some of the issues noted include frame rate drops for PC players using VSync, world textures that render too slowly after you respawn, and poor audio quality and / or temporary interruptions for voice chat. (nonfictiongaming.com)
Project Butter's aim is to make Android run at a solid 60 fps, complete with triple buffering and forced vsync. (trustedreviews.com)