Why is it so hard to talk about faith with my non-believing friends?

I work with a bunch of guys who I genuinely like and respect. We hang out on weekends sometimes. But I feel like I'm hiding a huge part of who I am by not talking about my faith more openly. I don't want to be that guy who's always preaching but I also feel like I'm being a coward. How do you balance being authentic without being preachy?