1 pc crankset for 20" bmx question

[Lugo175]

hey guy wondering if i can get some help,
i just bought some bmx bikes with out a crankset but upcycled from a frame(unknown size) but the chain is still loose and it slides off after a while that my son ride it , i have pulled the tire back but still not tight on chain
please bare with me , is there a diffrence in cranksets on BMX's that are smaller say 16"-18 vs 20" size bike
thank you

 

[mitchelangelo]

Some have a smaller throw or reach. Measure the length from center of crank to pedal.

 

[mikeeebikey]

I think the o.p. is looking for a bigger chainring, to take up more chain, correct?
Yes they make all sizes of sprockets!
It will probably be a trip to the local bike shop to have the chain shortened a link, or buy a chain tool.

 

[Bicycle808]

You got shorter chainstays on the 20". Shorten the chain.

 

[Lugo175]

thank you guys whwnt to shop and they chop the chain to fit now runs tight went on our first rid for 2 miles friday night and no issues :lol: