I really like your style, the stroke of the brush showing through makes for a very cool effect. It gives the picture a whole lot of motion regardless of what it is.
That’s kind of the problem with girl’s pose - she is extremely stiff on the bike. Never have a person’s line of motion just going straight up and down if you want to insinuate speed. You can go either way, have her hunched towards the machine, giving her a fierce look of concentration. Alternately, you could have her arched back, as if the thing she’s riding is going so fast she can barely hold on. Right now, the girl is just sitting straight up, it makes it look like she’s having a job interview. I also have no idea what those red things are in the foreground. They look sort of like a low wall, due to the fact they overlap the bike a bit at the bottom. If that’s the case, it looks as if she’s going to run right into it. Maybe clear up what that is on the bottom of the page. The last thing I’ve noticed is her ‘shirt’. The fabric looks like it’s just hanging there, maybe have the bottom pieces that are hanging be pulled in the appropriate direction (like the cape on her back)?
I love the costume, especially the helmet/headdress she’s wearing. The chariot she’s riding is also really neat, conceptually. Good job!