im starting to bmx ive been doing it for about 2 weeks now l was wondering what it does to butt and thighs does it make them slimmer or bigger? how long does it take?

it will strengthen the muscle.

It depends on how you ride. Cycling with a high cadence and lite pressure will slim your muscles and make then harder and pedaling at slow rpm is and mashing on the pedals will build larger muscles but they wont last as long. l am not sure how long BMX riders ride their bikes without coasting or jumping but if want to really lose weight get a road bike.

well l feel it all on my thighs, my thighs have become alot bigger/stronger lately. l feel it on the butt only if l ride a road bike.

? is right l ride a road bike and my butt and thighs are hard as a rock when flexed