15lbs and up! It depends upon what the bike is made of. The department store bmx bikes are the heaviest more in the 25lb+ range. If your looking to actually race bmx. A retail bmx is not a good...
Very much depends on what kind of MTB you're looking for, and waht you're ready to spend on it. A high-end XC(cross country) MTB can be around 20-22 lbs(less than 10 kg). For an FS DH MTB (full...