In Mauville city, Rydel at Rydel's Cycles lets you switch bikes. I've already completed the entire game, but he still only lets me switch bikes.
How do I get him to give me both bikes? I've heard you need to ride the bikes around a lot, but I've been riding them for a while now. If this is true, how many steps do I need to ride them?
Best Answer
The two bikes are necessary for getting some items in a variety of areas including the Safari Zone and various Mirage Caves. To get both bikes, you need to advertise Rydel's Bikes to 3 different people throughout the region
Once you have spoken to all three of these characters, return to Rydel's Cycles in Mauville City and he will give you the other bike, so you now have both bikes at the same time.
From Pokemon ORAS Bicycles - Serebii