I'm traveling from Montargis train stop to Melun (R line RER) and I'd like to bring my non folded bike with me. I'm traveling on Saturday early morning. Can I bring a bike on a train RER? Thank you for your time.
You can bring your bike on Transilien trains at any time of day on weekends. The Transilien R between Melun/Montargis included.
More info on bringing bikes on Paris trains.