You will get the Bicycle just before reaching Nimbasa City. The owner of the daycare will give you the Bicycle for free after you’ve saved him from the Team Plasma grunts. This event is part of the main story and is unmissable.
But before you’re able to reach Nimbasa City, you’ll need to defeat Gym Leader Burgh in Castelia City and cross the sandstorm on Route 4.
Getting the Bicycle
Step 1: Starting at the Castelia City Pokémon Center, head down the alley directly to the right of the Center.
Step 2: Continue north down Castelia Street towards the street’s exit.
Step 3: Castelia Street’s exit leads to the Central plaza.
Continue north across the plaza.
Step 4: Keep north past the water fountain and exit the plaza.
Step 5: After exiting the plaza, walk north through the green tunnel to exit Castelia City.
Step 6: The green tunnel leads to Route 4. Head north on that route.
Step 7: Keep north on Route 4 and keep moving forward past the Trainer Tips sign.
Step 8: The path leading north brings you into a heavy sandstorm. Just keep north through the sand.
Step 9: Continue past the hiking trainers and head towards the three traffic cones on the unfinished paved road.
Step 10: Above Route 4 is a bridge overpass. Keep moving north through to the other side of the overpass (you’ll walk under it).
Step 11: Just ahead is a green tunnel.
Exit through that tunnel to reach Nimbasa City.
Step 12: At the entrance of Nimbasa City you’ll find the Daycare owner surrounded by two Team Plasma grunts. The Daycare owner will ask for your help.
Step 13: After defeating one of the grunts in battle, the Daycare owner will reward you with the Bicycle.
Using The Bicycle
Compared to previous generations, Black and White’s Bicycle is without fancy frills such as extra gears or riding types. You could think of it more akin to the Gen 1/Gen 2 Bikes.
However, the Bicycle is super fast in B&W – it can travel about 8 steps per second.
It’s also worth noting that the Black & White Bicycle isn’t needed to climb slopes or reach special areas anywhere in the game. So you could technically finish the game on foot.
The speed boost is worth it though, and riding the Bicycle makes hatching eggs a much quicker process.
Tip: Once you have your bike, you’re able to bind it to the Y-button for quick and easy access.