If you're looking for manga similar to Gen-Cha!, you might like these titles.
For the last three years, the motocross national B-League has been dominated by Kurosu Gen. He has been unmatched in his riding skills and no one was surprised when Gen was promoted to the A-League, the highest league in the nation. But this division has been ruled by an even bigger monster than Gen, the Red Army and its leader Igarashi Shunichi. For the last 5 years, the Red Army has left the competition in the dust and won the championship with ease. Gen is determined to put an end to the Red Army dynasty and take first place but the caliber of motocross riders here are heads and shoulders above what he has seen before.
Yoshio is a girl, and she likes to ride a motorcycle! She wants to be the best and compete in the Grand Battle tournament. But there are many obstacles on her road to victory.
Takeshi Hongo is an expert motorcycle racer and a young genius with an IQ of 400. He is abducted by the secretive company Shocker and turned into a cyborg as part of a fiendish plot to take over the world. Just before his brain is irrevocably transformed, Hongo manages to escape his hidden prison with the assistance of his respected teacher Dr. Midorikawa, a scientific genius who has been forced to work for Shocker. Hongo, with his indomitable spirit and sense of justice, names himself the Masked Rider and uses his motorcycle, Cyclone, and the superhuman powers imbued in him by Shocker to combat the organization's evil ambitions!