Yep if you run 25-9 or whatever, and you put out big power like a pro BMXer does chances are you will either strip the teeth on the rear sprocket or the chain will just jump over the teeth on the rear sprocket. Because remember that the chain is only on probably 4 out of the 9 teeth. Not much metal to put 500W or whatever through.Because if you are putting real power to the ground like pro BMXers, then you will snap a standard chain using a smaller chainring. Thus you have to get a bigger chain, and negate all weight savings. As said before, its about clearance and stalls etc. for the street, IF you are putting out real power. However, most street riders are not comparable to BMX racers in the power department.