Ever since the original Pokemon Red and Blue, players have had access to a bicycle in the game to get around quicker, especially before obtaining Fly. However, the Gen III games Ruby and Sapphire introduced a whole new mechanic to the bike system with the Acro Bike and the Mach Bike, both of which have made their triumphant return in Pokemon Omega Ruby and Alpha Sapphire.
After obtaining the bicycle so early in Pokemon X and Y in the same city as the second gym, many may be expecting the same in Pokemon Omega Ruby and Alpha Sapphire, especially after residents of Slateport City start to discuss the bike and you see Cycling Roads you cannot access. Do not fret, as you will soon be able to obtain one.
As soon as you enter Mauville City, which is almost entirely indoors, you will see bicycles everywhere in the area. This means you are on the right track. Head for the right-middle side and when there, you will see a store with bicycles in a window. Head inside and speak with the owner Rydel, who will give you the much needed bicycle.
However, as said above, you will have the option of two bikes, the Mach Bike or the Acro Bike, which are as follows:
You do not just have to choose one permanently either, as you can always return to Rydel and switch. However, Pokemon Omega Ruby and Alpha Sapphire add in something not seen in the originals though, the ability to obtain both. To do this, you must show a bike to three specific trainers across Hoenn.
After doing all three, go speak with Rydel at his shop once again and you will gain the ability to have both.