Find a gear that works for you! For me that was generally 42x16 back in the day and now 46x17 but that is me. You probably want to ride a road bike with other road bikers if you are having trouble or just don't bother keeping up with them and go on your own ride, they might appreciate it more. On descents on a fixed gear unless running a ridiculous gear you couldn't run elsewhere except downhill there is no gear you won't likely spin out on it is downhill.