Ride the bike in French

Bonjour Lixin 

"The basic rule is fairly simple: if you can go into the vehicle, use en – otherwise use à.

en bus, en avion, en train, en voiture, en bateau…
à moto, à vélo, à pied, à trottinette…"

The above Is from WorkReference.com 

I could not find a post more appropriate to your Kwiziq query than the quoted lesson.

Hope this helps.

Bonne continuation

Jim