Thanks, but are BMX freewheels the same as or compatible with our single-speed bicycles? Are they the same part numbers?

What the advantage of going to a 42 on the chainwheel vs 18 on the freewheel cog? I have a FSA Tempo crank set which does not seem to yield much for parts or places to order a smaller 42 chainwheel?

Just as a side note, I spin around 100 RPM and ride a lot in my 53/25 on my geared bikes which is 56GI and 16.5MPH. I need to get down a long ways .