Welcome! Our biker comunity is not so big but we have our moments
Most of rides are happening during weekend, and most of us from Belgrade and like 30km around are gravitate towards this place https://www.google.rs/maps/place/Кота+555/@44.1254098,20.4839359,17z/data=!3m1!4b1!4m6!3m5!1s0x475744179e3957eb:0xe28ed979e6bbc734!8m2!3d44.125406!4d20.4865108!16s%2Fg%2F11g_m_6kp?hl=sr&entry=ttu&g_ep=EgoyMDI1MDMwOC4wIKXMDSoASAFQAw%3D%3D
During season this is a place of gathering...afcourse there are a lot of diferent places in Serbia that you can visit with bike. Danube gorge, Pešter highlands, various mountains sutable for riding etc.
just explore this forum and you will find something nice for you.