1. Go to your (Steam) Libary
2. Find Need For Speed Rivals
3. Press the settings icon for the game
4. Select properties
5. Go to Launch Options
6. Paste these 2 commands in: -GameTime.MaxSimFps 60 -GameTime.ForceSimRate 60.0
7. Press enter and restart the game if you had it open while making these changes

Boom! Now Need For Speed Rivals will be locked at 60 FPS. You can set the FPS lower or higher but please note that any FPS over 50 may break the game due to the engine being made to run at 30 FPS.