Hi all, I live in Madrid and work about one mile from IFEMA. I would not recommend you rent a Bike to move around. IFEMA is not located close to the city. It´s actually closer to the Airport. So renting a BIKE would probably be useless unless you want to do some exercise. I wish I could write something different.
The Best option is definitely the METRO.
Enjoy your stay here,
Perfect info @JuanCa thanks!